Message-Id: <20171228135856.GB24720@rapoport-lnx>
Date:   Thu, 28 Dec 2017 15:58:57 +0200
From:   Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+aa0386edb3e128ffa315@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        syzkaller-bugs@...glegroups.com, Linux-MM <linux-mm@...ck.org>
Subject: Re: WARNING in __wake_up_common

On Thu, Dec 28, 2017 at 10:30:46AM +0100, Dmitry Vyukov wrote:
> On Thu, Dec 28, 2017 at 10:20 AM, syzbot
> <syzbot+aa0386edb3e128ffa315@...kaller.appspotmail.com> wrote:
> > Hello,
> >
> > syzkaller hit the following crash on
> > 82bcf1def3b5f1251177ad47c44f7e17af039b4b
> > git://git.cmpxchg.org/linux-mmots.git/master
> > compiler: gcc (GCC) 7.1.1 20170620
> > .config is attached
> > Raw console output is attached.
> > C reproducer is attached
> > syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> > for information about syzkaller reproducers
> >
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+aa0386edb3e128ffa315@...kaller.appspotmail.com
> > It will help syzbot understand when the bug is fixed. See footer for
> > details.
> > If you forward the report, please keep this part and the footer.
> >
> > audit: type=1400 audit(1513711793.237:7): avc:  denied  { map } for
> > pid=3151 comm="syzkaller173649" path="/root/syzkaller173649879" dev="sda1"
> > ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
> > tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
> > WARNING: CPU: 1 PID: 3151 at kernel/sched/wait.c:79
> > __wake_up_common+0x433/0x770 kernel/sched/wait.c:79
> > Kernel panic - not syncing: panic_on_warn set ...
> >
> > CPU: 1 PID: 3151 Comm: syzkaller173649 Not tainted 4.15.0-rc2-mm1+ #39
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > Call Trace:
> >  __dump_stack lib/dump_stack.c:17 [inline]
> >  dump_stack+0x194/0x257 lib/dump_stack.c:53
> >  panic+0x1e4/0x41c kernel/panic.c:183
> >  __warn+0x1dc/0x200 kernel/panic.c:547
> >  report_bug+0x211/0x2d0 lib/bug.c:184
> >  fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:177
> >  fixup_bug arch/x86/kernel/traps.c:246 [inline]
> >  do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:295
> >  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:314
> >  invalid_op+0x22/0x40 arch/x86/entry/entry_64.S:1079
> > RIP: 0010:__wake_up_common+0x433/0x770 kernel/sched/wait.c:79
> > RSP: 0018:ffff8801c4897648 EFLAGS: 00010246
> > RAX: 0000000000000000 RBX: ffff8801d8cbfe50 RCX: 0000000000000004
> > RDX: 1ffffffff0c59731 RSI: ffff8801d8cbfe68 RDI: 0000000000000282
> > RBP: ffff8801c4897748 R08: ffff8801c4897858 R09: 0000000000000000
> > R10: 000000000000000b R11: ffffed0038912e48 R12: 0000000000000000
> > R13: ffff8801d8cbfe00 R14: 0000000000000001 R15: ffff8801c4897858
> >  __wake_up_locked_key+0x16/0x20 kernel/sched/wait.c:166
> >  userfaultfd_release+0x4da/0x750 fs/userfaultfd.c:885
> >  __fput+0x333/0x7f0 fs/file_table.c:210
> >  ____fput+0x15/0x20 fs/file_table.c:244
> >  task_work_run+0x199/0x270 kernel/task_work.c:113
> >  exit_task_work include/linux/task_work.h:22 [inline]
> >  do_exit+0x9bb/0x1ae0 kernel/exit.c:869
> >  do_group_exit+0x149/0x400 kernel/exit.c:972
> >  SYSC_exit_group kernel/exit.c:983 [inline]
> >  SyS_exit_group+0x1d/0x20 kernel/exit.c:981
> >  entry_SYSCALL_64_fastpath+0x1f/0x96
> > RIP: 0033:0x43e848
> > RSP: 002b:00007ffe33766e08 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> > RAX: ffffffffffffffda RBX: 00000000006ca800 RCX: 000000000043e848
> > RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
> > RBP: 00000000000014b1 R08: 00000000000000e7 R09: ffffffffffffffd0
> > R10: 0000000000000006 R11: 0000000000000246 R12: 00000000006ca858
> > R13: 00000000006ca858 R14: 0000000000000000 R15: 0000000000002710
> > Dumping ftrace buffer:
> >    (ftrace buffer empty)
> > Kernel Offset: disabled
> > Rebooting in 86400 seconds..
> 
> 
> This was triggered by just creating a userfaultfd, and happened only
> in mmots but stopped happening few days ago. I don't see any recent
> commits touching useffaultfd.c in mm tree (other than
> "mm/userfaultfd.c: remove duplicate include"). Was a bogus commit
> dropped from mm tree? Let's close this bug for now and see if it
> happens again:
 
Seems to me it's the same problem as one reported by 01day bot [1].

There was Christoph's patch "sched/wait: assert the wait_queue_head lock is
held in __wake_up_common" that Andrew dropped from his tree.
This patch revealed, hmm, special wait queue locking in the userfault.

[1] https://lkml.org/lkml/2017/12/13/942

> #syz invalid
> 
> 
> > ---
> > This bug is generated by a dumb bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for details.
> > Direct all questions to syzkaller@...glegroups.com.
> >
> > syzbot will keep track of this bug report.
> > If you forgot to add the Reported-by tag, once the fix for this bug is
> > merged
> > into any tree, please reply to this email with:
> > #syz fix: exact-commit-title
> > If you want to test a patch for this bug, please reply with:
> > #syz test: git://repo/address.git branch
> > and provide the patch inline or as an attachment.
> > To mark this as a duplicate of another syzbot report, please reply with:
> > #syz dup: exact-subject-of-another-report
> > If it's a one-off invalid bug report, please reply with:
> > #syz invalid
> > Note: if the crash happens again, it will cause creation of a new bug
> > report.
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> >
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-- 
Sincerely yours,
Mike.

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