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Date: Mon, 01 Dec 2014 16:08:20 -0500
From: Kurt Miller <kurt@...ricatesoftware.com>
To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: 3.10 page_fault/mmap_sem/hugepages deadlock
On 3.10.0-123.9.3.el7.x86_64 I am seeing a deadlock on mmap_sem which
causes ps(1) and similar utilities to freeze and our application to stop
functioning. Looking at the kernel crash dump (first time for me), it
looks like a page fault on a huge page is holding the mmap_sem and then
goes to sleep. The other processes such as khugepaged, ps(1), pgrep(1)
and netstat(8) are all blocked on mmap_sem and are unkillable with kill
-9.
The back trace for the suspect problem page fault looks like this:
crash> bt -l 2045
PID: 2045 TASK: ffff881002f35b00 CPU: 22 COMMAND: "icd"
#0 [ffff880fdc9edbe8] __schedule at ffffffff815e75fd
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/kernel/sched/core.c: 2164
#1 [ffff880fdc9edc50] io_schedule at ffffffff815e7e5d
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/arch/x86/include/asm/current.h: 14
#2 [ffff880fdc9edc68] sleep_on_page at ffffffff8114112e
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/mm/filemap.c: 247
#3 [ffff880fdc9edc78] __wait_on_bit at ffffffff815e5c20
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/kernel/wait.c: 203
#4 [ffff880fdc9edcb8] wait_on_page_bit at ffffffff81140eb6
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/mm/filemap.c: 691
#5 [ffff880fdc9edd10] wait_migrate_huge_page at ffffffff8119b7fb
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/mm/migrate.c: 1670
#6 [ffff880fdc9edd20] do_huge_pmd_numa_page at ffffffff8119e62f
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/mm/huge_memory.c: 1315
#7 [ffff880fdc9edd98] handle_mm_fault at ffffffff8116c324
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/mm/memory.c: 3748
#8 [ffff880fdc9ede28] __do_page_fault at ffffffff815edb06
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/arch/x86/mm/fault.c: 1193
#9 [ffff880fdc9edf28] do_page_fault at ffffffff815edf0a
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/arch/x86/mm/fault.c: 1233
#10 [ffff880fdc9edf50] page_fault at ffffffff815ea148
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/arch/x86/kernel/entry_64.S: 1511
RIP: 000000000046e9da RSP: 00007fb0cf52bdc0 RFLAGS: 00010202
RAX: 00007fb0af1c4ec0 RBX: 00007fb06c000c00 RCX: b88ef6a13246e1d9
RDX: c130973455498b41 RSI: 00007fb0b1b96000 RDI: 00007fb0af1c4ec0
RBP: 00007fb0cf52be10 R8: 0000000000000000 R9: 00000000000007fd
R10: 0000000000000000 R11: 00007fb0dac86280 R12: 0000000000000000
R13: 00007fb0cf52d9c0 R14: 00007fb0cf52d700 R15: 0000000000000000
ORIG_RAX: ffffffffffffffff CS: 0033 SS: 002b
In frame 8, __do_page_fault() calls down_read(&mm->mmap_sem) on line 1138
and looks like it is holding it when it calls handle_mm_fault() on line 1193.
It looks like handle_mm_fault() eventually sleeps holding mmap_sem and doesn't
wake up.
The above process is hung up like ps(1) and friends and unkillable with kill -9.
khugepaged is blocked waiting for mmap_sem as well in frame 4 below:
crash> bt -l 206
PID: 206 TASK: ffff8808043138e0 CPU: 7 COMMAND: "khugepaged"
#0 [ffff881001d7bc48] __schedule at ffffffff815e75fd
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/kernel/sched/core.c: 2164
#1 [ffff881001d7bcb0] schedule at ffffffff815e7b39
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/kernel/sched/core.c: 3215
#2 [ffff881001d7bcc0] rwsem_down_read_failed at ffffffff815e9655
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/lib/rwsem.c: 179
#3 [ffff881001d7bd70] down_read at ffffffff815e6f20
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/kernel/rwsem.c: 24
#4 [ffff881001d7bd88] khugepaged_scan_mm_slot at ffffffff8119cd24
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/arch/x86/include/asm/atomic.h: 25
#5 [ffff881001d7be48] khugepaged at ffffffff8119dbaf
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/include/linux/spinlock.h: 333
#6 [ffff881001d7bec8] kthread at ffffffff81085aff
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/kernel/kthread.c: 200
#7 [ffff881001d7bf50] ret_from_fork at ffffffff815f29ec
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/arch/x86/kernel/entry_64.S: 570
ps(1), pgrep(1) and netstat(8) are all blocked in the same way.
__access_remote_vm() is blocked waiting on down_read(&mm->mmap_sem).
I'll include one back trace as an example:
crash> bt -l 8846
PID: 8846 TASK: ffff880fff78f1c0 CPU: 19 COMMAND: "ps"
#0 [ffff880f30431c68] __schedule at ffffffff815e75fd
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/kernel/sched/core.c: 2164
#1 [ffff880f30431cd0] schedule at ffffffff815e7b39
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/kernel/sched/core.c: 3215
#2 [ffff880f30431ce0] rwsem_down_read_failed at ffffffff815e9655
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/lib/rwsem.c: 179
#3 [ffff880f30431d50] call_rwsem_down_read_failed at ffffffff812c6414
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/arch/x86/lib/rwsem.S: 94
#4 [ffff880f30431db0] __access_remote_vm at ffffffff8116d251
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/mm/memory.c: 4022
#5 [ffff880f30431e40] access_process_vm at ffffffff8116e090
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/mm/memory.c: 4104
#6 [ffff880f30431e80] proc_pid_cmdline at ffffffff81217a2a
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/fs/proc/base.c: 222
#7 [ffff880f30431ec0] proc_info_read at ffffffff81218e8f
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/fs/proc/base.c: 654
#8 [ffff880f30431f08] vfs_read at ffffffff811af57c
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/fs/read_write.c: 388
#9 [ffff880f30431f38] sys_read at ffffffff811b00a8
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/fs/read_write.c: 489
#10 [ffff880f30431f80] system_call_fastpath at ffffffff815f2a99
/usr/src/debug/kernel-3.10.0-123.9.3.el7/linux-3.10.0-123.9.3.el7.x86_64/arch/x86/kernel/entry_64.S: 645
RIP: 00007fa31a3a5ce0 RSP: 00007fffe3b13d48 RFLAGS: 00000246
RAX: 0000000000000000 RBX: ffffffff815f2a99 RCX: ffffffffffffffff
RDX: 0000000000020000 RSI: 00007fa31ae80010 RDI: 0000000000000006
RBP: 0000000000020000 R8: 00007fa31a306dff R9: 0000000000000012
R10: 0000000000000007 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa31ae80010 R14: 0000000000000000 R15: 00007fa31ae80010
ORIG_RAX: 0000000000000000 CS: 0033 SS: 002b
I searched the archives for similar reports and found this thread from 2010:
http://marc.info/?l=linux-kernel&m=127005640811303&w=2
But that seems like it was resolved long ago.
Please let me know if any additional information is needed to help
diagnose the problem. I can reproduce it under heavy load in about
24 hours.
Regards,
-Kurt
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