* Re: possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem [not found] <20170807140947.nhfz2gel6wytl6ia@shodan.usersys.redhat.com> @ 2017-08-16 14:07 ` Thomas Gleixner 2017-08-30 14:15 ` Michal Hocko 0 siblings, 1 reply; 10+ messages in thread From: Thomas Gleixner @ 2017-08-16 14:07 UTC (permalink / raw) To: Artem Savkov Cc: Paul E. McKenney, LKML, Michal Hocko, Johannes Weiner, linux-mm On Mon, 7 Aug 2017, Artem Savkov wrote: +Cc mm folks ... > Hello, > > After commit fc8dffd "cpu/hotplug: Convert hotplug locking to percpu rwsem" > the following lockdep splat started showing up on some systems while running > ltp's madvise06 test (right after first dirty_pages call [1]). > > [1] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/madvise/madvise06.c#L136 > > [21002.630252] ====================================================== > [21002.637148] WARNING: possible circular locking dependency detected > [21002.644045] 4.13.0-rc3-next-20170807 #12 Not tainted > [21002.649583] ------------------------------------------------------ > [21002.656492] a.out/4771 is trying to acquire lock: > [21002.661742] (cpu_hotplug_lock.rw_sem){++++++}, at: [<ffffffff812b4668>] drain_all_stock.part.35+0x18/0x140 > [21002.672629] > [21002.672629] but task is already holding lock: > [21002.679137] (&mm->mmap_sem){++++++}, at: [<ffffffff8106eb35>] __do_page_fault+0x175/0x530 > [21002.688371] > [21002.688371] which lock already depends on the new lock. > [21002.688371] > [21002.697505] > [21002.697505] the existing dependency chain (in reverse order) is: > [21002.705856] > [21002.705856] -> #3 (&mm->mmap_sem){++++++}: > [21002.712080] lock_acquire+0xc9/0x230 > [21002.716661] __might_fault+0x70/0xa0 > [21002.721241] _copy_to_user+0x23/0x70 > [21002.725814] filldir+0xa7/0x110 > [21002.729988] xfs_dir2_sf_getdents.isra.10+0x20c/0x2c0 [xfs] > [21002.736840] xfs_readdir+0x1fa/0x2c0 [xfs] > [21002.742042] xfs_file_readdir+0x30/0x40 [xfs] > [21002.747485] iterate_dir+0x17a/0x1a0 > [21002.752057] SyS_getdents+0xb0/0x160 > [21002.756638] entry_SYSCALL_64_fastpath+0x1f/0xbe > [21002.762371] > [21002.762371] -> #2 (&type->i_mutex_dir_key#3){++++++}: > [21002.769661] lock_acquire+0xc9/0x230 > [21002.774239] down_read+0x51/0xb0 > [21002.778429] lookup_slow+0xde/0x210 > [21002.782903] walk_component+0x160/0x250 > [21002.787765] link_path_walk+0x1a6/0x610 > [21002.792625] path_openat+0xe4/0xd50 > [21002.797100] do_filp_open+0x91/0x100 > [21002.801673] file_open_name+0xf5/0x130 > [21002.806429] filp_open+0x33/0x50 > [21002.810620] kernel_read_file_from_path+0x39/0x80 > [21002.816459] _request_firmware+0x39f/0x880 > [21002.821610] request_firmware_direct+0x37/0x50 > [21002.827151] request_microcode_fw+0x64/0xe0 > [21002.832401] reload_store+0xf7/0x180 > [21002.836974] dev_attr_store+0x18/0x30 > [21002.841641] sysfs_kf_write+0x44/0x60 > [21002.846318] kernfs_fop_write+0x113/0x1a0 > [21002.851374] __vfs_write+0x37/0x170 > [21002.855849] vfs_write+0xc7/0x1c0 > [21002.860128] SyS_write+0x58/0xc0 > [21002.864313] do_syscall_64+0x6c/0x1f0 > [21002.868973] return_from_SYSCALL_64+0x0/0x7a > [21002.874317] > [21002.874317] -> #1 (microcode_mutex){+.+.+.}: > [21002.880748] lock_acquire+0xc9/0x230 > [21002.885322] __mutex_lock+0x88/0x960 > [21002.889894] mutex_lock_nested+0x1b/0x20 > [21002.894854] microcode_init+0xbb/0x208 > [21002.899617] do_one_initcall+0x51/0x1a9 > [21002.904481] kernel_init_freeable+0x208/0x2a7 > [21002.909922] kernel_init+0xe/0x104 > [21002.914298] ret_from_fork+0x2a/0x40 > [21002.918867] > [21002.918867] -> #0 (cpu_hotplug_lock.rw_sem){++++++}: > [21002.926058] __lock_acquire+0x153c/0x1550 > [21002.931112] lock_acquire+0xc9/0x230 > [21002.935688] cpus_read_lock+0x4b/0x90 > [21002.940353] drain_all_stock.part.35+0x18/0x140 > [21002.945987] try_charge+0x3ab/0x6e0 > [21002.950460] mem_cgroup_try_charge+0x7f/0x2c0 > [21002.955902] shmem_getpage_gfp+0x25f/0x1050 > [21002.961149] shmem_fault+0x96/0x200 > [21002.965621] __do_fault+0x1e/0xa0 > [21002.969905] __handle_mm_fault+0x9c3/0xe00 > [21002.975056] handle_mm_fault+0x16e/0x380 > [21002.980013] __do_page_fault+0x24a/0x530 > [21002.984968] do_page_fault+0x30/0x80 > [21002.989537] page_fault+0x28/0x30 > [21002.993812] > [21002.993812] other info that might help us debug this: > [21002.993812] > [21003.002744] Chain exists of: > [21003.002744] cpu_hotplug_lock.rw_sem --> &type->i_mutex_dir_key#3 --> &mm->mmap_sem > [21003.002744] > [21003.016238] Possible unsafe locking scenario: > [21003.016238] > [21003.022843] CPU0 CPU1 > [21003.027896] ---- ---- > [21003.032948] lock(&mm->mmap_sem); > [21003.036741] lock(&type->i_mutex_dir_key#3); > [21003.044419] lock(&mm->mmap_sem); > [21003.051025] lock(cpu_hotplug_lock.rw_sem); > [21003.055788] > [21003.055788] *** DEADLOCK *** > [21003.055788] > [21003.062393] 2 locks held by a.out/4771: > [21003.066675] #0: (&mm->mmap_sem){++++++}, at: [<ffffffff8106eb35>] __do_page_fault+0x175/0x530 > [21003.076391] #1: (percpu_charge_mutex){+.+...}, at: [<ffffffff812b4c97>] try_charge+0x397/0x6e0 > [21003.086198] > [21003.086198] stack backtrace: > [21003.091059] CPU: 6 PID: 4771 Comm: a.out Not tainted 4.13.0-rc3-next-20170807 #12 > [21003.099409] Hardware name: Dell Inc. PowerEdge M520/0DW6GX, BIOS 2.4.2 02/03/2015 > [21003.107766] Call Trace: > [21003.110495] dump_stack+0x85/0xc9 > [21003.114190] print_circular_bug+0x1f9/0x207 > [21003.118854] __lock_acquire+0x153c/0x1550 > [21003.123327] lock_acquire+0xc9/0x230 > [21003.127313] ? drain_all_stock.part.35+0x18/0x140 > [21003.132563] cpus_read_lock+0x4b/0x90 > [21003.136652] ? drain_all_stock.part.35+0x18/0x140 > [21003.141900] drain_all_stock.part.35+0x18/0x140 > [21003.146954] try_charge+0x3ab/0x6e0 > [21003.150846] mem_cgroup_try_charge+0x7f/0x2c0 > [21003.155705] shmem_getpage_gfp+0x25f/0x1050 > [21003.160374] shmem_fault+0x96/0x200 > [21003.164263] ? __lock_acquire+0x2fb/0x1550 > [21003.168832] ? __lock_acquire+0x2fb/0x1550 > [21003.173402] __do_fault+0x1e/0xa0 > [21003.177097] __handle_mm_fault+0x9c3/0xe00 > [21003.181669] handle_mm_fault+0x16e/0x380 > [21003.186045] ? handle_mm_fault+0x49/0x380 > [21003.190518] __do_page_fault+0x24a/0x530 > [21003.194895] do_page_fault+0x30/0x80 > [21003.198883] page_fault+0x28/0x30 > [21003.202593] RIP: 0033:0x400886 > [21003.205998] RSP: 002b:00007fff81d84d20 EFLAGS: 00010206 > [21003.211827] RAX: 00007fc763bb7000 RBX: 0000000000000000 RCX: 0000000000001000 > [21003.219789] RDX: 0000000006362000 RSI: 0000000019000000 RDI: 00007fc75d855000 > [21003.227751] RBP: 00007fff81d84d50 R08: ffffffffffffffff R09: 0000000000000000 > [21003.235713] R10: 00007fff81d84a30 R11: 00007fc7769445d0 R12: 0000000000400750 > [21003.243681] R13: 00007fff81d84f70 R14: 0000000000000000 R15: 0000000000000000 > > -- > Regards, > Artem > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem 2017-08-16 14:07 ` possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem Thomas Gleixner @ 2017-08-30 14:15 ` Michal Hocko 2017-08-30 15:43 ` Michal Hocko 0 siblings, 1 reply; 10+ messages in thread From: Michal Hocko @ 2017-08-30 14:15 UTC (permalink / raw) To: Thomas Gleixner Cc: Artem Savkov, Paul E. McKenney, LKML, Johannes Weiner, linux-mm On Wed 16-08-17 16:07:21, Thomas Gleixner wrote: > On Mon, 7 Aug 2017, Artem Savkov wrote: > > +Cc mm folks ... Ups, this has fallen through cracks > > Hello, > > > > After commit fc8dffd "cpu/hotplug: Convert hotplug locking to percpu rwsem" > > the following lockdep splat started showing up on some systems while running > > ltp's madvise06 test (right after first dirty_pages call [1]). > > > > [1] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/madvise/madvise06.c#L136 > > > > [21002.630252] ====================================================== > > [21002.637148] WARNING: possible circular locking dependency detected > > [21002.644045] 4.13.0-rc3-next-20170807 #12 Not tainted > > [21002.649583] ------------------------------------------------------ > > [21002.656492] a.out/4771 is trying to acquire lock: > > [21002.661742] (cpu_hotplug_lock.rw_sem){++++++}, at: [<ffffffff812b4668>] drain_all_stock.part.35+0x18/0x140 > > [21002.672629] > > [21002.672629] but task is already holding lock: > > [21002.679137] (&mm->mmap_sem){++++++}, at: [<ffffffff8106eb35>] __do_page_fault+0x175/0x530 [...] > > [21002.993812] other info that might help us debug this: > > [21002.993812] > > [21003.002744] Chain exists of: > > [21003.002744] cpu_hotplug_lock.rw_sem --> &type->i_mutex_dir_key#3 --> &mm->mmap_sem > > [21003.002744] > > [21003.016238] Possible unsafe locking scenario: > > [21003.016238] > > [21003.022843] CPU0 CPU1 > > [21003.027896] ---- ---- > > [21003.032948] lock(&mm->mmap_sem); > > [21003.036741] lock(&type->i_mutex_dir_key#3); > > [21003.044419] lock(&mm->mmap_sem); > > [21003.051025] lock(cpu_hotplug_lock.rw_sem); OK, this smells like the same thing we had to address for drain_all_pages by a459eeb7b852 ("mm, page_alloc: do not depend on cpu hotplug locks inside the allocator"). try_charge might be deep in the call path so taking cpu_hotplug_lock just calls for troubles. I have of course forgot all the subtle details about drain_all_pages but re-reading the changelog it seems that we can get along with droping {get,put}_online_cpus in because drain_local_stock (which is called from the WQ context as well) is disabling irqs and _always_ operates on the local cpu stock. So we cannot possibly race with the memory hotplug AFAICS. So what do you think about the following patch? --- ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem 2017-08-30 14:15 ` Michal Hocko @ 2017-08-30 15:43 ` Michal Hocko 2017-08-31 11:10 ` Artem Savkov 2017-09-04 14:03 ` Michal Hocko 0 siblings, 2 replies; 10+ messages in thread From: Michal Hocko @ 2017-08-30 15:43 UTC (permalink / raw) To: Thomas Gleixner Cc: Artem Savkov, Paul E. McKenney, LKML, Johannes Weiner, linux-mm The previous patch is insufficient. drain_all_stock can still race with the memory offline callback and the underlying memcg disappear. So we need to be more careful and pin the css on the memcg. This patch instead... --- ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem 2017-08-30 15:43 ` Michal Hocko @ 2017-08-31 11:10 ` Artem Savkov 2017-08-31 12:09 ` Michal Hocko 2017-09-04 14:03 ` Michal Hocko 1 sibling, 1 reply; 10+ messages in thread From: Artem Savkov @ 2017-08-31 11:10 UTC (permalink / raw) To: Michal Hocko Cc: Thomas Gleixner, Paul E. McKenney, LKML, Johannes Weiner, linux-mm Hi Michal, On Wed, Aug 30, 2017 at 05:43:15PM +0200, Michal Hocko wrote: > The previous patch is insufficient. drain_all_stock can still race with > the memory offline callback and the underlying memcg disappear. So we > need to be more careful and pin the css on the memcg. This patch > instead... Tried this on top of rc7 and it does fix the splat for me. > --- > From 70a5acf9bbe76d183e81a1a6b57dd5b9edc677c6 Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@suse.com> > Date: Wed, 30 Aug 2017 16:09:01 +0200 > Subject: [PATCH] mm, memcg: remove hotplug locking from try_charge > > The following lockde splat has been noticed during LTP testing > > [21002.630252] ====================================================== > [21002.637148] WARNING: possible circular locking dependency detected > [21002.644045] 4.13.0-rc3-next-20170807 #12 Not tainted > [21002.649583] ------------------------------------------------------ > [21002.656492] a.out/4771 is trying to acquire lock: > [21002.661742] (cpu_hotplug_lock.rw_sem){++++++}, at: [<ffffffff812b4668>] drain_all_stock.part.35+0x18/0x140 > [21002.672629] > [21002.672629] but task is already holding lock: > [21002.679137] (&mm->mmap_sem){++++++}, at: [<ffffffff8106eb35>] __do_page_fault+0x175/0x530 > [21002.688371] > [21002.688371] which lock already depends on the new lock. > [21002.688371] > [21002.697505] > [21002.697505] the existing dependency chain (in reverse order) is: > [21002.705856] > [21002.705856] -> #3 (&mm->mmap_sem){++++++}: > [21002.712080] lock_acquire+0xc9/0x230 > [21002.716661] __might_fault+0x70/0xa0 > [21002.721241] _copy_to_user+0x23/0x70 > [21002.725814] filldir+0xa7/0x110 > [21002.729988] xfs_dir2_sf_getdents.isra.10+0x20c/0x2c0 [xfs] > [21002.736840] xfs_readdir+0x1fa/0x2c0 [xfs] > [21002.742042] xfs_file_readdir+0x30/0x40 [xfs] > [21002.747485] iterate_dir+0x17a/0x1a0 > [21002.752057] SyS_getdents+0xb0/0x160 > [21002.756638] entry_SYSCALL_64_fastpath+0x1f/0xbe > [21002.762371] > [21002.762371] -> #2 (&type->i_mutex_dir_key#3){++++++}: > [21002.769661] lock_acquire+0xc9/0x230 > [21002.774239] down_read+0x51/0xb0 > [21002.778429] lookup_slow+0xde/0x210 > [21002.782903] walk_component+0x160/0x250 > [21002.787765] link_path_walk+0x1a6/0x610 > [21002.792625] path_openat+0xe4/0xd50 > [21002.797100] do_filp_open+0x91/0x100 > [21002.801673] file_open_name+0xf5/0x130 > [21002.806429] filp_open+0x33/0x50 > [21002.810620] kernel_read_file_from_path+0x39/0x80 > [21002.816459] _request_firmware+0x39f/0x880 > [21002.821610] request_firmware_direct+0x37/0x50 > [21002.827151] request_microcode_fw+0x64/0xe0 > [21002.832401] reload_store+0xf7/0x180 > [21002.836974] dev_attr_store+0x18/0x30 > [21002.841641] sysfs_kf_write+0x44/0x60 > [21002.846318] kernfs_fop_write+0x113/0x1a0 > [21002.851374] __vfs_write+0x37/0x170 > [21002.855849] vfs_write+0xc7/0x1c0 > [21002.860128] SyS_write+0x58/0xc0 > [21002.864313] do_syscall_64+0x6c/0x1f0 > [21002.868973] return_from_SYSCALL_64+0x0/0x7a > [21002.874317] > [21002.874317] -> #1 (microcode_mutex){+.+.+.}: > [21002.880748] lock_acquire+0xc9/0x230 > [21002.885322] __mutex_lock+0x88/0x960 > [21002.889894] mutex_lock_nested+0x1b/0x20 > [21002.894854] microcode_init+0xbb/0x208 > [21002.899617] do_one_initcall+0x51/0x1a9 > [21002.904481] kernel_init_freeable+0x208/0x2a7 > [21002.909922] kernel_init+0xe/0x104 > [21002.914298] ret_from_fork+0x2a/0x40 > [21002.918867] > [21002.918867] -> #0 (cpu_hotplug_lock.rw_sem){++++++}: > [21002.926058] __lock_acquire+0x153c/0x1550 > [21002.931112] lock_acquire+0xc9/0x230 > [21002.935688] cpus_read_lock+0x4b/0x90 > [21002.940353] drain_all_stock.part.35+0x18/0x140 > [21002.945987] try_charge+0x3ab/0x6e0 > [21002.950460] mem_cgroup_try_charge+0x7f/0x2c0 > [21002.955902] shmem_getpage_gfp+0x25f/0x1050 > [21002.961149] shmem_fault+0x96/0x200 > [21002.965621] __do_fault+0x1e/0xa0 > [21002.969905] __handle_mm_fault+0x9c3/0xe00 > [21002.975056] handle_mm_fault+0x16e/0x380 > [21002.980013] __do_page_fault+0x24a/0x530 > [21002.984968] do_page_fault+0x30/0x80 > [21002.989537] page_fault+0x28/0x30 > [21002.993812] > [21002.993812] other info that might help us debug this: > [21002.993812] > [21003.002744] Chain exists of: > [21003.002744] cpu_hotplug_lock.rw_sem --> &type->i_mutex_dir_key#3 --> &mm->mmap_sem > [21003.002744] > [21003.016238] Possible unsafe locking scenario: > [21003.016238] > [21003.022843] CPU0 CPU1 > [21003.027896] ---- ---- > [21003.032948] lock(&mm->mmap_sem); > [21003.036741] lock(&type->i_mutex_dir_key#3); > [21003.044419] lock(&mm->mmap_sem); > [21003.051025] lock(cpu_hotplug_lock.rw_sem); > [21003.055788] > [21003.055788] *** DEADLOCK *** > [21003.055788] > [21003.062393] 2 locks held by a.out/4771: > [21003.066675] #0: (&mm->mmap_sem){++++++}, at: [<ffffffff8106eb35>] __do_page_fault+0x175/0x530 > [21003.076391] #1: (percpu_charge_mutex){+.+...}, at: [<ffffffff812b4c97>] try_charge+0x397/0x6e0 > > The problem is very similar to the one fixed by a459eeb7b852 ("mm, > page_alloc: do not depend on cpu hotplug locks inside the allocator"). > We are taking hotplug locks while we can be sitting on top of basically > arbitrary locks. This just calls for problems. > > We can get rid of {get,put}_online_cpus, fortunately. We do not have to > be worried about races with memory hotplug because drain_local_stock, > which is called from both the WQ draining and the memory hotplug > contexts, is always operating on the local cpu stock with IRQs disabled. > > The only thing to be careful about is that the target memcg doesn't > vanish while we are still in drain_all_stock so take a reference on > it. > > Signed-off-by: Michal Hocko <mhocko@suse.com> > --- > mm/memcontrol.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index b9cf3cf4a3d0..5c70f47abb3d 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1765,6 +1765,10 @@ static void drain_local_stock(struct work_struct *dummy) > struct memcg_stock_pcp *stock; > unsigned long flags; > > + /* > + * The only protection from memory hotplug vs. drain_stock races is > + * that we always operate on local CPU stock here with IRQ disabled > + */ > local_irq_save(flags); > > stock = this_cpu_ptr(&memcg_stock); > @@ -1807,26 +1811,27 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) > if (!mutex_trylock(&percpu_charge_mutex)) > return; > /* Notify other cpus that system-wide "drain" is running */ > - get_online_cpus(); > curcpu = get_cpu(); > for_each_online_cpu(cpu) { > struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu); > struct mem_cgroup *memcg; > > memcg = stock->cached; > - if (!memcg || !stock->nr_pages) > + if (!memcg || !stock->nr_pages || !css_tryget(&memcg->css)) > continue; > - if (!mem_cgroup_is_descendant(memcg, root_memcg)) > + if (!mem_cgroup_is_descendant(memcg, root_memcg)) { > + css_put(&memcg->css); > continue; > + } > if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) { > if (cpu == curcpu) > drain_local_stock(&stock->work); > else > schedule_work_on(cpu, &stock->work); > } > + css_put(&memcg->css); > } > put_cpu(); > - put_online_cpus(); > mutex_unlock(&percpu_charge_mutex); > } > > -- > 2.13.2 > > -- > Michal Hocko > SUSE Labs -- Regards, Artem -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem 2017-08-31 11:10 ` Artem Savkov @ 2017-08-31 12:09 ` Michal Hocko 2017-08-31 12:19 ` Artem Savkov 0 siblings, 1 reply; 10+ messages in thread From: Michal Hocko @ 2017-08-31 12:09 UTC (permalink / raw) To: Artem Savkov Cc: Thomas Gleixner, Paul E. McKenney, LKML, Johannes Weiner, linux-mm On Thu 31-08-17 13:10:06, Artem Savkov wrote: > Hi Michal, > > On Wed, Aug 30, 2017 at 05:43:15PM +0200, Michal Hocko wrote: > > The previous patch is insufficient. drain_all_stock can still race with > > the memory offline callback and the underlying memcg disappear. So we > > need to be more careful and pin the css on the memcg. This patch > > instead... > > Tried this on top of rc7 and it does fix the splat for me. Thanks for testing! Can I assume your Tested-by? -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem 2017-08-31 12:09 ` Michal Hocko @ 2017-08-31 12:19 ` Artem Savkov 0 siblings, 0 replies; 10+ messages in thread From: Artem Savkov @ 2017-08-31 12:19 UTC (permalink / raw) To: Michal Hocko Cc: Thomas Gleixner, Paul E. McKenney, LKML, Johannes Weiner, linux-mm On Thu, Aug 31, 2017 at 02:09:51PM +0200, Michal Hocko wrote: > On Thu 31-08-17 13:10:06, Artem Savkov wrote: > > Hi Michal, > > > > On Wed, Aug 30, 2017 at 05:43:15PM +0200, Michal Hocko wrote: > > > The previous patch is insufficient. drain_all_stock can still race with > > > the memory offline callback and the underlying memcg disappear. So we > > > need to be more careful and pin the css on the memcg. This patch > > > instead... > > > > Tried this on top of rc7 and it does fix the splat for me. > > Thanks for testing! Can I assume your Tested-by? Didn't test much more than the case that was causing it, but yes. Reported-and-tested-by: Artem Savkov <asavkov@redhat.com> -- Regards, Artem -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem 2017-08-30 15:43 ` Michal Hocko 2017-08-31 11:10 ` Artem Savkov @ 2017-09-04 14:03 ` Michal Hocko 2017-09-05 8:19 ` Thomas Gleixner 1 sibling, 1 reply; 10+ messages in thread From: Michal Hocko @ 2017-09-04 14:03 UTC (permalink / raw) To: Thomas Gleixner, Johannes Weiner Cc: Artem Savkov, Paul E. McKenney, LKML, linux-mm Thomas, Johannes, could you double check my thinking here? I will repost the patch to Andrew if you are OK with this. On Wed 30-08-17 17:43:15, Michal Hocko wrote: > The previous patch is insufficient. drain_all_stock can still race with > the memory offline callback and the underlying memcg disappear. So we > need to be more careful and pin the css on the memcg. This patch > instead... > --- > From 70a5acf9bbe76d183e81a1a6b57dd5b9edc677c6 Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@suse.com> > Date: Wed, 30 Aug 2017 16:09:01 +0200 > Subject: [PATCH] mm, memcg: remove hotplug locking from try_charge > > The following lockde splat has been noticed during LTP testing > > [21002.630252] ====================================================== > [21002.637148] WARNING: possible circular locking dependency detected > [21002.644045] 4.13.0-rc3-next-20170807 #12 Not tainted > [21002.649583] ------------------------------------------------------ > [21002.656492] a.out/4771 is trying to acquire lock: > [21002.661742] (cpu_hotplug_lock.rw_sem){++++++}, at: [<ffffffff812b4668>] drain_all_stock.part.35+0x18/0x140 > [21002.672629] > [21002.672629] but task is already holding lock: > [21002.679137] (&mm->mmap_sem){++++++}, at: [<ffffffff8106eb35>] __do_page_fault+0x175/0x530 > [21002.688371] > [21002.688371] which lock already depends on the new lock. > [21002.688371] > [21002.697505] > [21002.697505] the existing dependency chain (in reverse order) is: > [21002.705856] > [21002.705856] -> #3 (&mm->mmap_sem){++++++}: > [21002.712080] lock_acquire+0xc9/0x230 > [21002.716661] __might_fault+0x70/0xa0 > [21002.721241] _copy_to_user+0x23/0x70 > [21002.725814] filldir+0xa7/0x110 > [21002.729988] xfs_dir2_sf_getdents.isra.10+0x20c/0x2c0 [xfs] > [21002.736840] xfs_readdir+0x1fa/0x2c0 [xfs] > [21002.742042] xfs_file_readdir+0x30/0x40 [xfs] > [21002.747485] iterate_dir+0x17a/0x1a0 > [21002.752057] SyS_getdents+0xb0/0x160 > [21002.756638] entry_SYSCALL_64_fastpath+0x1f/0xbe > [21002.762371] > [21002.762371] -> #2 (&type->i_mutex_dir_key#3){++++++}: > [21002.769661] lock_acquire+0xc9/0x230 > [21002.774239] down_read+0x51/0xb0 > [21002.778429] lookup_slow+0xde/0x210 > [21002.782903] walk_component+0x160/0x250 > [21002.787765] link_path_walk+0x1a6/0x610 > [21002.792625] path_openat+0xe4/0xd50 > [21002.797100] do_filp_open+0x91/0x100 > [21002.801673] file_open_name+0xf5/0x130 > [21002.806429] filp_open+0x33/0x50 > [21002.810620] kernel_read_file_from_path+0x39/0x80 > [21002.816459] _request_firmware+0x39f/0x880 > [21002.821610] request_firmware_direct+0x37/0x50 > [21002.827151] request_microcode_fw+0x64/0xe0 > [21002.832401] reload_store+0xf7/0x180 > [21002.836974] dev_attr_store+0x18/0x30 > [21002.841641] sysfs_kf_write+0x44/0x60 > [21002.846318] kernfs_fop_write+0x113/0x1a0 > [21002.851374] __vfs_write+0x37/0x170 > [21002.855849] vfs_write+0xc7/0x1c0 > [21002.860128] SyS_write+0x58/0xc0 > [21002.864313] do_syscall_64+0x6c/0x1f0 > [21002.868973] return_from_SYSCALL_64+0x0/0x7a > [21002.874317] > [21002.874317] -> #1 (microcode_mutex){+.+.+.}: > [21002.880748] lock_acquire+0xc9/0x230 > [21002.885322] __mutex_lock+0x88/0x960 > [21002.889894] mutex_lock_nested+0x1b/0x20 > [21002.894854] microcode_init+0xbb/0x208 > [21002.899617] do_one_initcall+0x51/0x1a9 > [21002.904481] kernel_init_freeable+0x208/0x2a7 > [21002.909922] kernel_init+0xe/0x104 > [21002.914298] ret_from_fork+0x2a/0x40 > [21002.918867] > [21002.918867] -> #0 (cpu_hotplug_lock.rw_sem){++++++}: > [21002.926058] __lock_acquire+0x153c/0x1550 > [21002.931112] lock_acquire+0xc9/0x230 > [21002.935688] cpus_read_lock+0x4b/0x90 > [21002.940353] drain_all_stock.part.35+0x18/0x140 > [21002.945987] try_charge+0x3ab/0x6e0 > [21002.950460] mem_cgroup_try_charge+0x7f/0x2c0 > [21002.955902] shmem_getpage_gfp+0x25f/0x1050 > [21002.961149] shmem_fault+0x96/0x200 > [21002.965621] __do_fault+0x1e/0xa0 > [21002.969905] __handle_mm_fault+0x9c3/0xe00 > [21002.975056] handle_mm_fault+0x16e/0x380 > [21002.980013] __do_page_fault+0x24a/0x530 > [21002.984968] do_page_fault+0x30/0x80 > [21002.989537] page_fault+0x28/0x30 > [21002.993812] > [21002.993812] other info that might help us debug this: > [21002.993812] > [21003.002744] Chain exists of: > [21003.002744] cpu_hotplug_lock.rw_sem --> &type->i_mutex_dir_key#3 --> &mm->mmap_sem > [21003.002744] > [21003.016238] Possible unsafe locking scenario: > [21003.016238] > [21003.022843] CPU0 CPU1 > [21003.027896] ---- ---- > [21003.032948] lock(&mm->mmap_sem); > [21003.036741] lock(&type->i_mutex_dir_key#3); > [21003.044419] lock(&mm->mmap_sem); > [21003.051025] lock(cpu_hotplug_lock.rw_sem); > [21003.055788] > [21003.055788] *** DEADLOCK *** > [21003.055788] > [21003.062393] 2 locks held by a.out/4771: > [21003.066675] #0: (&mm->mmap_sem){++++++}, at: [<ffffffff8106eb35>] __do_page_fault+0x175/0x530 > [21003.076391] #1: (percpu_charge_mutex){+.+...}, at: [<ffffffff812b4c97>] try_charge+0x397/0x6e0 > > The problem is very similar to the one fixed by a459eeb7b852 ("mm, > page_alloc: do not depend on cpu hotplug locks inside the allocator"). > We are taking hotplug locks while we can be sitting on top of basically > arbitrary locks. This just calls for problems. > > We can get rid of {get,put}_online_cpus, fortunately. We do not have to > be worried about races with memory hotplug because drain_local_stock, > which is called from both the WQ draining and the memory hotplug > contexts, is always operating on the local cpu stock with IRQs disabled. > > The only thing to be careful about is that the target memcg doesn't > vanish while we are still in drain_all_stock so take a reference on > it. > > Signed-off-by: Michal Hocko <mhocko@suse.com> > --- > mm/memcontrol.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index b9cf3cf4a3d0..5c70f47abb3d 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1765,6 +1765,10 @@ static void drain_local_stock(struct work_struct *dummy) > struct memcg_stock_pcp *stock; > unsigned long flags; > > + /* > + * The only protection from memory hotplug vs. drain_stock races is > + * that we always operate on local CPU stock here with IRQ disabled > + */ > local_irq_save(flags); > > stock = this_cpu_ptr(&memcg_stock); > @@ -1807,26 +1811,27 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) > if (!mutex_trylock(&percpu_charge_mutex)) > return; > /* Notify other cpus that system-wide "drain" is running */ > - get_online_cpus(); > curcpu = get_cpu(); > for_each_online_cpu(cpu) { > struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu); > struct mem_cgroup *memcg; > > memcg = stock->cached; > - if (!memcg || !stock->nr_pages) > + if (!memcg || !stock->nr_pages || !css_tryget(&memcg->css)) > continue; > - if (!mem_cgroup_is_descendant(memcg, root_memcg)) > + if (!mem_cgroup_is_descendant(memcg, root_memcg)) { > + css_put(&memcg->css); > continue; > + } > if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) { > if (cpu == curcpu) > drain_local_stock(&stock->work); > else > schedule_work_on(cpu, &stock->work); > } > + css_put(&memcg->css); > } > put_cpu(); > - put_online_cpus(); > mutex_unlock(&percpu_charge_mutex); > } > > -- > 2.13.2 > > -- > Michal Hocko > SUSE Labs -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem 2017-09-04 14:03 ` Michal Hocko @ 2017-09-05 8:19 ` Thomas Gleixner 2017-09-05 10:23 ` Michal Hocko 0 siblings, 1 reply; 10+ messages in thread From: Thomas Gleixner @ 2017-09-05 8:19 UTC (permalink / raw) To: Michal Hocko Cc: Johannes Weiner, Artem Savkov, Paul E. McKenney, LKML, linux-mm On Mon, 4 Sep 2017, Michal Hocko wrote: > Thomas, Johannes, > could you double check my thinking here? I will repost the patch to > Andrew if you are OK with this. > > + /* > > + * The only protection from memory hotplug vs. drain_stock races is > > + * that we always operate on local CPU stock here with IRQ disabled > > + */ > > local_irq_save(flags); > > > > stock = this_cpu_ptr(&memcg_stock); > > @@ -1807,26 +1811,27 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) > > if (!mutex_trylock(&percpu_charge_mutex)) > > return; > > /* Notify other cpus that system-wide "drain" is running */ > > - get_online_cpus(); > > curcpu = get_cpu(); The problem here is that this does only protect you against a CPU being unplugged, but not against a CPU coming online concurrently. I have no idea whether that might be a problem, but at least you should put a comment in which explains why it is not. Thanks, tglx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem 2017-09-05 8:19 ` Thomas Gleixner @ 2017-09-05 10:23 ` Michal Hocko 2017-09-05 11:04 ` Thomas Gleixner 0 siblings, 1 reply; 10+ messages in thread From: Michal Hocko @ 2017-09-05 10:23 UTC (permalink / raw) To: Thomas Gleixner Cc: Johannes Weiner, Artem Savkov, Paul E. McKenney, LKML, linux-mm On Tue 05-09-17 10:19:13, Thomas Gleixner wrote: > On Mon, 4 Sep 2017, Michal Hocko wrote: > > > Thomas, Johannes, > > could you double check my thinking here? I will repost the patch to > > Andrew if you are OK with this. > > > + /* > > > + * The only protection from memory hotplug vs. drain_stock races is > > > + * that we always operate on local CPU stock here with IRQ disabled > > > + */ > > > local_irq_save(flags); > > > > > > stock = this_cpu_ptr(&memcg_stock); > > > @@ -1807,26 +1811,27 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) > > > if (!mutex_trylock(&percpu_charge_mutex)) > > > return; > > > /* Notify other cpus that system-wide "drain" is running */ > > > - get_online_cpus(); > > > curcpu = get_cpu(); > > The problem here is that this does only protect you against a CPU being > unplugged, but not against a CPU coming online concurrently. Yes but same as the drain_all_pages we do not have any cpu up specific intialization so there is no specific action to race against AFAICS. > I have no idea > whether that might be a problem, but at least you should put a comment in > which explains why it is not. What about this? --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5c70f47abb3d..ff9b0979ccc3 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1810,7 +1810,12 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) /* If someone's already draining, avoid adding running more workers. */ if (!mutex_trylock(&percpu_charge_mutex)) return; - /* Notify other cpus that system-wide "drain" is running */ + /* + * Notify other cpus that system-wide "drain" is running + * We do not care about races with the cpu hotplug because cpu down + * as well as workers from this path always operate on the local + * per-cpu data. CPU up doesn't touch memcg_stock at all. + */ curcpu = get_cpu(); for_each_online_cpu(cpu) { struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu); -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem 2017-09-05 10:23 ` Michal Hocko @ 2017-09-05 11:04 ` Thomas Gleixner 0 siblings, 0 replies; 10+ messages in thread From: Thomas Gleixner @ 2017-09-05 11:04 UTC (permalink / raw) To: Michal Hocko Cc: Johannes Weiner, Artem Savkov, Paul E. McKenney, LKML, linux-mm On Tue, 5 Sep 2017, Michal Hocko wrote: > On Tue 05-09-17 10:19:13, Thomas Gleixner wrote: > > On Mon, 4 Sep 2017, Michal Hocko wrote: > > > > > Thomas, Johannes, > > > could you double check my thinking here? I will repost the patch to > > > Andrew if you are OK with this. > > > > + /* > > > > + * The only protection from memory hotplug vs. drain_stock races is > > > > + * that we always operate on local CPU stock here with IRQ disabled > > > > + */ > > > > local_irq_save(flags); > > > > > > > > stock = this_cpu_ptr(&memcg_stock); > > > > @@ -1807,26 +1811,27 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) > > > > if (!mutex_trylock(&percpu_charge_mutex)) > > > > return; > > > > /* Notify other cpus that system-wide "drain" is running */ > > > > - get_online_cpus(); > > > > curcpu = get_cpu(); > > > > The problem here is that this does only protect you against a CPU being > > unplugged, but not against a CPU coming online concurrently. > > Yes but same as the drain_all_pages we do not have any cpu up specific > intialization so there is no specific action to race against AFAICS. > > > I have no idea > > whether that might be a problem, but at least you should put a comment in > > which explains why it is not. > > What about this? Looks good. > --- > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 5c70f47abb3d..ff9b0979ccc3 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1810,7 +1810,12 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) > /* If someone's already draining, avoid adding running more workers. */ > if (!mutex_trylock(&percpu_charge_mutex)) > return; > - /* Notify other cpus that system-wide "drain" is running */ > + /* > + * Notify other cpus that system-wide "drain" is running > + * We do not care about races with the cpu hotplug because cpu down > + * as well as workers from this path always operate on the local > + * per-cpu data. CPU up doesn't touch memcg_stock at all. > + */ > curcpu = get_cpu(); > for_each_online_cpu(cpu) { > struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu); > > -- > Michal Hocko > SUSE Labs > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 10+ messages in thread
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2017-08-16 14:07 ` possible circular locking dependency mmap_sem/cpu_hotplug_lock.rw_sem Thomas Gleixner
2017-08-30 14:15 ` Michal Hocko
2017-08-30 15:43 ` Michal Hocko
2017-08-31 11:10 ` Artem Savkov
2017-08-31 12:09 ` Michal Hocko
2017-08-31 12:19 ` Artem Savkov
2017-09-04 14:03 ` Michal Hocko
2017-09-05 8:19 ` Thomas Gleixner
2017-09-05 10:23 ` Michal Hocko
2017-09-05 11:04 ` Thomas Gleixner
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