Re: 2.6.26-rc5-mm2

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Tue, 2008-06-10 at 17:28 +1000, Nick Piggin wrote:
> On Tuesday 10 June 2008 15:31, Andrew Morton wrote:
> > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.26-rc5/2.
> >6.26-rc5-mm2/
> >
> 
> BTW. would be trying to test this more myself, but last mm I based the
> lockless patches on didn't boot, and this one dies pretty quickly when
> you try to get into reclaim:
> 
> ------------[ cut here ]------------
> kernel BUG at mm/swap_state.c:77!
> invalid opcode: 0000 [1] SMP DEBUG_PAGEALLOC
> last sysfs file: /sys/devices/system/cpu/cpu7/cache/index2/shared_cpu_map
> CPU 7
> Modules linked in:
> Pid: 13550, comm: sh Not tainted 2.6.26-rc5-mm2-dirty #412
> RIP: 0010:[<ffffffff80288689>]  [<ffffffff80288689>] 
> add_to_swap_cache+0xd9/0x120
> RSP: 0018:ffff81010c62d8a8  EFLAGS: 00010246
> RAX: 2000000000020009 RBX: ffffe2000107da88 RCX: c000000000000000
> RDX: 0000000000000020 RSI: 000000000000eea2 RDI: ffffe2000107da88
> RBP: ffff81010c62d8c8 R08: fffffffffa48016e R09: 0000000000000000
> R10: ffffffff80857fa0 R11: 2222222222222222 R12: ffff81012e126520
> R13: 000000000000eea2 R14: ffff8100727bea20 R15: ffff81010c62d9b8
> FS:  00002b5b33cafdc0(0000) GS:ffff81012ff07800(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: 000000000175e280 CR3: 000000012e292000 CR4: 00000000000006e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process sh (pid: 13550, threadinfo ffff81010c62c000, task ffff810116b01110)
> Stack:  ffff81010c62d8c8 ffffe2000107da88 ffff81012e126520 ffff81012e126400
>  ffff81010c62d908 ffffffff80292851 000000000000eea2 ffff81012e126708
>  ffffe2000107da88 ffffffff80701420 ffff81010c62db68 ffff81010c62dc88
> Call Trace:
>  [<ffffffff80292851>] shmem_writepage+0x121/0x200
>  [<ffffffff80277479>] shrink_page_list+0x559/0x6b0
>  [<ffffffff802777ec>] shrink_list+0x21c/0x520
>  [<ffffffff80273365>] ? determine_dirtyable_memory+0x15/0x30
>  [<ffffffff802733a2>] ? get_dirty_limits+0x22/0x2a0
>  [<ffffffff80277d31>] shrink_zone+0x241/0x330
>  [<ffffffff80278207>] try_to_free_pages+0x237/0x3a0
>  [<ffffffff80276530>] ? isolate_pages_global+0x0/0x270
>  [<ffffffff80272546>] __alloc_pages_internal+0x206/0x4b0
>  [<ffffffff8028dfd7>] alloc_pages_current+0x87/0xd0
>  [<ffffffff802714fe>] __get_free_pages+0xe/0x60
>  [<ffffffff802343ca>] copy_process+0xba/0x1240
>  [<ffffffff80235682>] do_fork+0x82/0x2a0
>  [<ffffffff8025a03d>] ? trace_hardirqs_on+0xd/0x10
>  [<ffffffff805177ab>] ? _spin_unlock_irq+0x2b/0x40
>  [<ffffffff8051703f>] ? trace_hardirqs_on_thunk+0x3a/0x3f
>  [<ffffffff8020b6cb>] ? system_call_after_swapgs+0x7b/0x80
>  [<ffffffff80209853>] sys_clone+0x23/0x30
> 
> The tmpfs PageSwapBacked stuff seems rather broken. For
> them write_begin/write_end path, it is filemap.c, not shmem.c,
> which allocates the page, so its no wonder it goes bug. Will
> try to do more testing without shmem.
> 
> Also, just noticed
> mm/memory.c:do_wp_page
> //TODO:  is this safe?  do_anonymous_page() does it this way.
> 
> That's a bit disheartening. Surely a question like that has to
> be answered definitively? (hopefully whatever is doing the
> asking won't get merged until answered)

I put those C++ TODO comments in there specifically to raise their
visibility in hopes that someone [like you :)] would notice and maybe
have an answer to the question.  I noted the issue in the change log as
well--i.e., that I had moved set_pte_at() to after the lru_cache_add and
'new_rmap.   The existing order may be that way for a reason, but it's
not clear [to me] what that reason is.  As I noted, do_anonymous_page()
sets the pte after the lru_add and new_rmap.

I agree, these questions need to be answered and the TODO's resolved
before merging.   Any thoughts as to the ordering?

Lee


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