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SubjectRe: deadlock on 2.6.24.3-rt3
Peter Zijlstra wrote:
> On Mon, 2008-03-17 at 21:53 -0400, Steven Rostedt wrote:
>> [Added Peter Zijlsta and LKML]
>
> Yeah, patches and such should really go to LKML as LKML is the -rt
> development list.

Sorry, I missed to add LKML. It's written in RT wiki.
I'm not sure about BUG report too. Should I send it to LKML?

>
>> Hiroshi, thanks for looking into this!
>>
>> Peter, this looks like a legit fix, could you Ack it.
>>
>>
>> On Mon, 17 Mar 2008, Hiroshi Shimamoto wrote:
>>
>>> Hiroshi Shimamoto wrote:
>>>> Hi,
>>>>
>>>> I got a soft lockup message on 2.6.24.3-rt3.
>>>> I attached the .config.
>>>>
>>>> I think there is a deadlock scenario, I explain later.
>>>>
>>>> Here is the console log;
>>>> BUG: soft lockup - CPU#2 stuck for 11s! [bash:2175]
>>>> CPU 2:
>>>> Modules linked in:
>>>> Pid: 2175, comm: bash Not tainted 2.6.24.3-rt3 #1
>>>> RIP: 0010:[<ffffffff8063f052>] [<ffffffff8063f052>] __spin_lock+0x57/0x67
>>>> RSP: 0000:ffff8100c52a1d48 EFLAGS: 00000202
>>>> RAX: 0000000000000000 RBX: 0000000000004bc5 RCX: 0000000000004bc5
>>>> RDX: 0000000000000002 RSI: 00000000006c3208 RDI: 0000000000000001
>>>> RBP: 000000000000000d R08: ffff8100cbc28018 R09: ffff810007c95458
>>>> R10: 00000000006c3208 R11: 0000000000000246 R12: ffffffff808246e8
>>>> R13: 000284d000000002 R14: ffffffff80387277 R15: 00000000ffffffff
>>>> FS: 00002b28926a2ef0(0000) GS:ffff8100cf8a3940(0000) knlGS:0000000000000000
>>>> CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>>> CR2: 00000000006c3208 CR3: 00000000c3cac000 CR4: 00000000000006e0
>>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>>>> Call Trace:
>>>> [<ffffffff8063f024>] __spin_lock+0x29/0x67
>>>> [<ffffffff80296597>] swap_info_get+0x65/0xdd
>>>> [<ffffffff80296c0c>] can_share_swap_page+0x39/0x84
>>>> [<ffffffff8028ae6e>] do_wp_page+0x2f9/0x519
>>>> [<ffffffff8028c8d2>] handle_mm_fault+0x615/0x7cf
>>>> [<ffffffff802db823>] proc_flush_task+0x171/0x29c
>>>> [<ffffffff8024a64d>] recalc_sigpending+0xe/0x3c
>>>> [<ffffffff8022645e>] do_page_fault+0x162/0x754
>>>> [<ffffffff8026fe81>] audit_syscall_exit+0x31c/0x37a
>>>> [<ffffffff8063f449>] error_exit+0x0/0x51
>>>> ---------------------------
>>>> | preempt count: 00010002 ]
>>>> | 2-level deep critical section nesting:
>>>> ----------------------------------------
>>>> .. [<ffffffff8063f009>] .... __spin_lock+0xe/0x67
>>>> .....[<00000000>] .. ( <= 0x0)
>>>> .. [<ffffffff8063f009>] .... __spin_lock+0xe/0x67
>>>> .....[<00000000>] .. ( <= 0x0)
>>>> BUG: soft lockup - CPU#3 stuck for 11s! [stress:9460]
>>>> CPU 3:
>>>> Modules linked in:
>>>> Pid: 9460, comm: stress Not tainted 2.6.24.3-rt3 #1
>>>> RIP: 0010:[<ffffffff8027c974>] [<ffffffff8027c974>] find_get_page+0xad/0xbe
>>>> RSP: 0018:ffff8100cbf25b88 EFLAGS: 00000202
>>>> 0000000000002009 RBX: ffffffff80824bc8 RCX: 0000000000000002
>>>> RDX: 0000000000000002 RSI: ffff8100cbfcf298 RDI: ffff810005ad8910
>>>> RBP: ffffffff80383a57 R08: ffff810005ad8918 R09: 0000000000000003
>>>> R10: ffff810005ad88d8 R11: 0000000000000001 R12: ffffffff80822880
>>>> R13: ffff81000799ce48 R14: ffffffff8028921c R15: ffffffff80822880
>>>> FS: 00002acaa373bb00(0000) GS:ffff8100cf8a32c0(0000) knlGS:0000000000000000
>>>> CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>>> CR2: 00002b9b2827c530 CR3: 000000006cc90000 CR4: 00000000000006e0
>>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>>>> Call Trace:
>>>> [<ffffffff8027c8ea>] find_get_page+0x23/0xbe
>>>> [<ffffffff80296f83>] free_swap_and_cache+0x46/0xdd
>>>> [<ffffffff8028b9b7>] unmap_vmas+0x626/0x8ce
>>>> [<ffffffff8028fa4c>] exit_mmap+0xac/0x147
>>>> [<ffffffff8023ced7>] mmput+0x32/0xae
>>>> [<ffffffff80242f00>] do_exit+0x199/0x914
>>>> [<ffffffff8024ab3b>] __dequeue_signal+0x19/0x1b7
>>>> [<ffffffff802436a7>] do_group_exit+0x2c/0x7e
>>>> [<ffffffff8024c47b>] get_signal_to_deliver+0x2ef/0x4aa
>>>> [<ffffffff8020b5dc>] do_notify_resume+0xa8/0x7cd
>>>> [<ffffffff80239320>] add_preempt_count+0x14/0x111
>>>> [<ffffffff8038b292>] __up_read+0x13/0x8d
>>>> [<ffffffff80226483>] do_page_fault+0x187/0x754
>>>> [<ffffffff802335ae>] __dequeue_entity+0x2d/0x34
>>>> [<ffffffff8020a6d5>] __switch_to+0x27/0x2c9
>>>> [<ffffffff802264f0>] do_page_fault+0x1f4/0x754
>>>> [<ffffffff8020c7be>] retint_signal+0x3d/0x7f
>>>> ---------------------------
>>>> | preempt count: 00010005 ]
>>>> | 5-level deep critical section nesting:
>>>> ----------------------------------------
>>>> .. [<ffffffff8063f009>] .... __spin_lock+0xe/0x67
>>>> .....[<00000000>] .. ( <= 0x0)
>>>> .. [<ffffffff8063f009>] .... __spin_lock+0xe/0x67
>>>> .....[<00000000>] .. ( <= 0x0)
>>>> .. [<ffffffff8063f009>] .... __spin_lock+0xe/0x67
>>>> .....[<00000000>] .. ( <= 0x0)
>>>> .. [<ffffffff8027c8db>] .... find_get_page+0x14/0xbe
>>>> .....[<00000000>] .. ( <= 0x0)
>>>> .. [<ffffffff8063f009>] .... __spin_lock+0xe/0x67
>>>> .....[<00000000>] .. ( <= 0x0)
>>>>
>>>>
>>>> I also got a kernel core.
>>>> (gdb) info thr
>>>> 4 process 9460 0xffffffff8027c974 in find_get_page (mapping=<value optimized out>,
>>>> offset=18446744071570598016) at include/asm/processor_64.h:385
>>>> 3 process 2175 __spin_lock (lock=0xffffffff80893f80) at kernel/spinlock.c:333
>>>> 2 process 9132 __spin_lock (lock=0xffffffff80893f80) at include/asm/spinlock_64.h:22
>>>> * 1 process 9478 __spin_lock (lock=0xffffffff80893f80) at kernel/spinlock.c:333
>>>>
>>>> CPU3(thread 4) is in find_get_page(), and the others in __spin_lock().
>>>> The thread 4 is waiting to turn PG_nonewrefs bit off in wait_on_page_ref() which is
>>>> called from page_cache_get_speculative(), and the thread 4 holds the swap_lock.
>>>> The other threads waiting the swap_lock.
>>>> On the other hand, the thread 1 turned PG_nonewrefs bit on by calling
>>>> lock_page_ref_irq() in remove_mapping(), and then waiting the swap_lock.
>>>> So if the target page of remove_mapping() is in the exiting process memory,
>>>> the kernel is deadlock.
>>>>
>>>> (gdb) bt
>>>> #0 __spin_lock (lock=0xffffffff80893f80) at kernel/spinlock.c:333
>>>> #1 0xffffffff80296597 in swap_info_get (entry=<value optimized out>)
>>>> at mm/swapfile.c:253
>>>> #2 0xffffffff80296618 in swap_free (entry={val = 1}) at mm/swapfile.c:300
>>>> #3 0xffffffff80286acd in remove_mapping (mapping=<value optimized out>,
>>>> page=0xffff810005ad8910) at mm/vmscan.c:423
>>>> ...
>>>>
>>>> (gdb) thr 2
>>>> (gdb) bt
>>>> #0 __spin_lock (lock=0xffffffff80893f80) at include/asm/spinlock_64.h:22
>>>> #1 0xffffffff80296374 in valid_swaphandles (entry=<value optimized out>,
>>>> offset=0xffff81001e22bc78) at mm/swapfile.c:1783
>>>> #2 0xffffffff8028b0af in swapin_readahead (entry={val = 1}, addr=0, vma=0x1)
>>>> at mm/memory.c:2054
>>>> #3 0xffffffff8029a6af in shmem_getpage (inode=0xffff8100cdf4fd48, idx=0,
>>>> pagep=0xffff81001e22bd80, sgp=SGP_FAULT, type=0xffff81001e22bd34) at mm/shmem.c:1089
>>>> ...
>>>>
>>>> (gdb) thr 3
>>>> (gdb) bt
>>>> #0 __spin_lock (lock=0xffffffff80893f80) at kernel/spinlock.c:333
>>>> #1 0xffffffff80296597 in swap_info_get (entry=<value optimized out>)
>>>> at mm/swapfile.c:253
>>>> #2 0xffffffff80296c0c in can_share_swap_page (page=<value optimized out>)
>>>> at mm/swapfile.c:317
>>>> #3 0xffffffff8028ae6e in do_wp_page (mm=0xffff8100ce772f40, vma=0xffff8100cd212f00,
>>>> address=7090696, page_table=0xffff8100cbcef618, pmd=0xffff8100cbc28018,
>>>> ptl=0xffff810007c95458, orig_pte=<value optimized out>) at mm/memory.c:1606
>>>> ...
>>>>
>>>> (gdb) thr 4
>>>> (gdb) bt
>>>> #0 0xffffffff8027c974 in find_get_page (mapping=<value optimized out>,
>>>> offset=18446744071570598016) at include/asm/processor_64.h:385
>>>> #1 0xffffffff80296f83 in free_swap_and_cache (entry={val = 4032}) at mm/swapfile.c:403
>>>> #2 0xffffffff8028b9b7 in unmap_vmas (tlbp=0xffff8100cbf25cd8, vma=0xffff8100cde5c678,
>>>> start_addr=0, end_addr=18446744073709551615, nr_accounted=0xffff8100cbf25cd0,
>>>> details=0x0) at mm/memory.c:728
>>>> #3 0xffffffff8028fa4c in exit_mmap (mm=0xffff8100cd093600) at mm/mmap.c:2048
>>>> #4 0xffffffff8023ced7 in mmput (mm=0xffff8100cd093600) at kernel/fork.c:443
>>>> #5 0xffffffff80242f00 in do_exit (code=14) at kernel/exit.c:997
>>>> ...
>>>>
>>>>
>>>> I think it came from the lockless speculative get page patch.
>>>> I found the newer version of this patch in linux-mm.
>>>> http://marc.info/?l=linux-mm&m=119477111927364&w=2
>>>>
>>>> I haven't tested it because it looks big change and hard to apply.
>>>> But it seems to fix this deadlock issue.
>>>> Any other patch to fix this issue is welcome.
>
> Yeah, in the latest lockless pagecache patches Nick got rid of
> PG_nonewrefs as suggested by Hugh, however -rt also has my concurrent
> pagecache patches and those need PG_nonewrefs on their own, so I hadn't
> bothered to update to Nick's latest.
>
> Perhaps I ought to, as you point out, page_cache_get_speculative() is
> cleaner in his latest.. /me puts it on his overlong TODO list.
>
>>> Is this patch good?
>
> Yes, it does look good. Doesn't remove_exclusice_swap_page() also nest
> PG_nonewrefs inside of swap_lock?

I'm not sure about it. I haven't noticed it and I haven't checked all PG_nonewrefs.
Will look into it.

By the way, unfortunately, I got another BUG message w/ my patch... I'll report it.
The new issue is related with SLAB.
kernel BUG at mm/slab.c:3125!

thanks,
Hiroshi Shimamoto


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