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R7UrYAjEhqnsxmDcTQZ8BgRtFW8uXYk3TynLlUMCj/0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jun 24, 2025 at 07:57:40AM -0700, Suren Baghdasaryan wrote: > On Tue, Jun 24, 2025 at 7:28 AM David Wang <00107082@163.com> wrote: > > > > > > At 2025-06-24 22:13:49, "Harry Yoo" wrote: > > >On Tue, Jun 24, 2025 at 10:00:48PM +0800, David Wang wrote: > > >> > > >> At 2025-06-24 21:50:02, "Harry Yoo" wrote: > > >> >On Tue, Jun 24, 2025 at 09:25:58PM +0800, David Wang wrote: > > >> >> > > >> >> At 2025-06-24 15:25:13, "Harry Yoo" wrote: > > >> >> >alloc_tag_top_users() attempts to lock alloc_tag_cttype->mod_lock > > >> >> >even when the alloc_tag_cttype is not allocated because: > > >> >> > > > >> >> > 1) alloc tagging is disabled because mem profiling is disabled > > >> >> > (!alloc_tag_cttype) > > >> >> > 2) alloc tagging is enabled, but not yet initialized (!alloc_tag_cttype) > > >> >> > 3) alloc tagging is enabled, but failed initialization > > >> >> > (!alloc_tag_cttype or IS_ERR(alloc_tag_cttype)) > > >> >> > > > >> >> >In all cases, alloc_tag_cttype is not allocated, and therefore > > >> >> >alloc_tag_top_users() should not attempt to acquire the semaphore. > > >> >> > > > >> >> >This leads to a crash on memory allocation failure by attempting to > > >> >> >acquire a non-existent semaphore: > > >> >> > > > >> >> > Oops: general protection fault, probably for non-canonical address 0xdffffc000000001b: 0000 [#3] SMP KASAN NOPTI > > >> >> > KASAN: null-ptr-deref in range [0x00000000000000d8-0x00000000000000df] > > >> >> > CPU: 2 UID: 0 PID: 1 Comm: systemd Tainted: G D 6.16.0-rc2 #1 VOLUNTARY > > >> >> > Tainted: [D]=DIE > > >> >> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 > > >> >> > RIP: 0010:down_read_trylock+0xaa/0x3b0 > > >> >> > Code: d0 7c 08 84 d2 0f 85 a0 02 00 00 8b 0d df 31 dd 04 85 c9 75 29 48 b8 00 00 00 00 00 fc ff df 48 8d 6b 68 48 89 ea 48 c1 ea 03 <80> 3c 02 00 0f 85 88 02 00 00 48 3b 5b 68 0f 85 53 01 00 00 65 ff > > >> >> > RSP: 0000:ffff8881002ce9b8 EFLAGS: 00010016 > > >> >> > RAX: dffffc0000000000 RBX: 0000000000000070 RCX: 0000000000000000 > > >> >> > RDX: 000000000000001b RSI: 000000000000000a RDI: 0000000000000070 > > >> >> > RBP: 00000000000000d8 R08: 0000000000000001 R09: ffffed107dde49d1 > > >> >> > R10: ffff8883eef24e8b R11: ffff8881002cec20 R12: 1ffff11020059d37 > > >> >> > R13: 00000000003fff7b R14: ffff8881002cec20 R15: dffffc0000000000 > > >> >> > FS: 00007f963f21d940(0000) GS:ffff888458ca6000(0000) knlGS:0000000000000000 > > >> >> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > >> >> > CR2: 00007f963f5edf71 CR3: 000000010672c000 CR4: 0000000000350ef0 > > >> >> > Call Trace: > > >> >> > > > >> >> > codetag_trylock_module_list+0xd/0x20 > > >> >> > alloc_tag_top_users+0x369/0x4b0 > > >> >> > __show_mem+0x1cd/0x6e0 > > >> >> > warn_alloc+0x2b1/0x390 > > >> >> > __alloc_frozen_pages_noprof+0x12b9/0x21a0 > > >> >> > alloc_pages_mpol+0x135/0x3e0 > > >> >> > alloc_slab_page+0x82/0xe0 > > >> >> > new_slab+0x212/0x240 > > >> >> > ___slab_alloc+0x82a/0xe00 > > >> >> > > > >> >> > > > >> >> >As David Wang points out, this issue became easier to trigger after commit > > >> >> >780138b12381 ("alloc_tag: check mem_profiling_support in alloc_tag_init"). > > >> >> > > > >> >> >Before the commit, the issue occurred only when it failed to allocate > > >> >> >and initialize alloc_tag_cttype or if a memory allocation fails before > > >> >> >alloc_tag_init() is called. After the commit, it can be easily triggered > > >> >> >when memory profiling is compiled but disabled at boot. > > >> >> > > > >> >> >To properly determine whether alloc_tag_init() has been called and > > >> >> >its data structures initialized, verify that alloc_tag_cttype is a valid > > >> >> >pointer before acquiring the semaphore. If the variable is NULL or an error > > >> >> >value, it has not been properly initialized. In such a case, just skip > > >> >> >and do not attempt to acquire the semaphore. > > >> >> > > > >> >> >Reported-by: kernel test robot > > >> >> >Closes: https://urldefense.com/v3/__https://lore.kernel.org/oe-lkp/202506181351.bba867dd-lkp@intel.com__;!!ACWV5N9M2RV99hQ!MADvGKtvTvlLXNxlrJ4BdOSnbsJlyrSroPUGJ3JQHs_IF-gxxqfQ89OTZ21aN96DbmjG9qH3Wi1MlgtiSA$ > > >> >> >Closes: https://urldefense.com/v3/__https://lore.kernel.org/oe-lkp/202506131711.5b41931c-lkp@intel.com__;!!ACWV5N9M2RV99hQ!MADvGKtvTvlLXNxlrJ4BdOSnbsJlyrSroPUGJ3JQHs_IF-gxxqfQ89OTZ21aN96DbmjG9qH3Wi0o2OoynA$ > > >> >> >Fixes: 780138b12381 ("alloc_tag: check mem_profiling_support in alloc_tag_init") > > >> >> >Fixes: 1438d349d16b ("lib: add memory allocations report in show_mem()") > > >> >> >Cc: stable@vger.kernel.org > > >> >> >Signed-off-by: Harry Yoo > > >> >> >--- > > >> >> > > > >> >> >@Suren: I did not add another pr_warn() because every error path in > > >> >> >alloc_tag_init() already has pr_err(). > > >> >> > > > >> >> >v2 -> v3: > > >> >> >- Added another Closes: tag (David) > > >> >> >- Moved the condition into a standalone if block for better readability > > >> >> > (Suren) > > >> >> >- Typo fix (Suren) > > >> >> > > > >> >> > lib/alloc_tag.c | 3 +++ > > >> >> > 1 file changed, 3 insertions(+) > > >> >> > > > >> >> >diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c > > >> >> >index 41ccfb035b7b..e9b33848700a 100644 > > >> >> >--- a/lib/alloc_tag.c > > >> >> >+++ b/lib/alloc_tag.c > > >> >> >@@ -127,6 +127,9 @@ size_t alloc_tag_top_users(struct codetag_bytes *tags, size_t count, bool can_sl > > >> >> > struct codetag_bytes n; > > >> >> > unsigned int i, nr = 0; > > >> >> > > > >> >> >+ if (IS_ERR_OR_NULL(alloc_tag_cttype)) > > >> >> >+ return 0; > > >> >> > > >> >> What about mem_profiling_support set to 0 after alloc_tag_init, in this case: > > >> >> alloc_tag_cttype != NULL && mem_profiling_support==0 > > >> >> > > >> >> I kind of think alloc_tag_top_users should return 0 in this case....and both mem_profiling_support and alloc_tag_cttype should be checked.... > > >> > > > >> >After commit 780138b12381, alloc_tag_cttype is not allocated if > > >> >!mem_profiling_support. (And that's why this bug showed up) > > >> > > >> There is a sysctl(/proc/sys/vm/mem_profiling) which can override mem_profiling_support and set it to 0, after alloc_tag_init with mem_profiling_support=1 > > Wait, /proc/sys/vm/mem_profiling is changing mem_alloc_profiling_key, > not mem_profiling_support. Am I missing something? Feels like it should call shutdown_mem_profiling() instead of proc_do_static_key() (and also remove /proc/allocinfo)? > > > > > >Ok. Maybe it shouldn't report memory allocation information that is > > >collected before mem profiling was disabled. (I'm not sure why it disabling > > >at runtime is allowed, though) > > > > > >That's a good thing to have, but I think that's a behavioral change in > > >mem profiling, irrelevant to this bug and not a -stable thing. > > > > > >Maybe as a follow-up patch? > > > > Only a little more changes needed, I was suggesting: > > > > @@ -134,6 +122,14 @@ size_t alloc_tag_top_users(struct codetag_bytes *tags, size_t count, bool can_sl > > struct codetag_bytes n; > > unsigned int i, nr = 0; > > > > + if (!mem_profiling_support) > > + return 0; > > David is right that with /proc/sys/vm/mem_profiling memory profiling > can be turned off at runtime but the above condition should be: > if (!mem_alloc_profiling_enabled()) > return 0; I agree that this change is a useful addition, but adding it to the patch doesn't look right. It's doing two different things. > > + > > + if (IS_ERR_OR_NULL(alloc_tag_cttype)) { > > + pr_warn("alloctag module is not ready yet.\n"); > > I don't think spitting out this warning on every show_mem() is useful. > If alloc_tag_cttype is invalid because codetag_register_type() failed > then we already print an error here: > https://elixir.bootlin.com/linux/v6.16-rc3/source/lib/alloc_tag.c#L829, > so user has the logs to track this down. > If show_mem() is called so early that alloc_tag_init() hasn't been > called yet then missing allocation tag information would not be > surprising I think, considering it's early boot. I don't think it's > worth detecting and reporting such a state. > > > + return 0; > > + } > > + -- Cheers, Harry / Hyeonggon