* INFO: task hung in exit_mm
@ 2019-07-01 8:27 syzbot
2019-07-02 0:14 ` Andrew Morton
0 siblings, 1 reply; 4+ messages in thread
From: syzbot @ 2019-07-01 8:27 UTC (permalink / raw)
To: aarcange, akpm, avagin, davem, ebiederm, linux-kernel, oleg,
prsood, syzkaller-bugs, tj
Hello,
syzbot found the following crash on:
HEAD commit: 249155c2 Merge branch 'parisc-5.2-4' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1306be61a00000
kernel config: https://syzkaller.appspot.com/x/.config?x=9a31528e58cc12e2
dashboard link: https://syzkaller.appspot.com/bug?extid=8cc1843d4eec9c0dfb35
compiler: clang version 9.0.0 (/home/glider/llvm/clang
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14a85379a00000
Bisection is inconclusive: the bug happens on the oldest tested release.
bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=119f6249a00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=139f6249a00000
console output: https://syzkaller.appspot.com/x/log.txt?x=159f6249a00000
IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8cc1843d4eec9c0dfb35@syzkaller.appspotmail.com
INFO: task syz-executor.0:8352 blocked for more than 143 seconds.
Not tainted 5.2.0-rc6+ #7
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.0 D24576 8352 8340 0x80004000
Call Trace:
context_switch kernel/sched/core.c:2818 [inline]
__schedule+0x658/0x9e0 kernel/sched/core.c:3445
schedule+0x131/0x1d0 kernel/sched/core.c:3509
__rwsem_down_read_failed_common+0x345/0x790 kernel/locking/rwsem-xadd.c:495
rwsem_down_read_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:515
__down_read+0x72/0x1a0 kernel/locking/rwsem.h:178
down_read+0x45/0x50 kernel/locking/rwsem.c:26
exit_mm+0xdb/0x630 kernel/exit.c:513
do_exit+0x5c3/0x2300 kernel/exit.c:864
do_group_exit+0x15c/0x2a0 kernel/exit.c:981
__do_sys_exit_group+0x17/0x20 kernel/exit.c:992
__se_sys_exit_group+0x14/0x20 kernel/exit.c:990
__x64_sys_exit_group+0x3b/0x40 kernel/exit.c:990
do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459519
Code: Bad RIP value.
RSP: 002b:00007ffdb1483048 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 000000000000001e RCX: 0000000000459519
RDX: 0000000000413201 RSI: fffffffffffffff7 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffffffffffff R09: 00007ffdb14830a0
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffdb14830a0 R14: 0000000000000000 R15: 00007ffdb14830b0
INFO: task syz-executor.0:8355 blocked for more than 143 seconds.
Not tainted 5.2.0-rc6+ #7
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.0 D25512 8355 8340 0x80004000
Call Trace:
context_switch kernel/sched/core.c:2818 [inline]
__schedule+0x658/0x9e0 kernel/sched/core.c:3445
schedule+0x131/0x1d0 kernel/sched/core.c:3509
__rwsem_down_read_failed_common+0x345/0x790 kernel/locking/rwsem-xadd.c:495
rwsem_down_read_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:515
__down_read+0x72/0x1a0 kernel/locking/rwsem.h:178
down_read+0x45/0x50 kernel/locking/rwsem.c:26
exit_mm+0xdb/0x630 kernel/exit.c:513
do_exit+0x5c3/0x2300 kernel/exit.c:864
do_group_exit+0x15c/0x2a0 kernel/exit.c:981
get_signal+0x6df/0x21f0 kernel/signal.c:2640
do_signal+0x7b/0x750 arch/x86/kernel/signal.c:815
exit_to_usermode_loop arch/x86/entry/common.c:164 [inline]
prepare_exit_to_usermode+0x2f5/0x4f0 arch/x86/entry/common.c:199
syscall_return_slowpath+0x110/0x440 arch/x86/entry/common.c:279
do_syscall_64+0x126/0x140 arch/x86/entry/common.c:304
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459519
Code: Bad RIP value.
RSP: 002b:00007f33b051bcf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 000000000075bfd0 RCX: 0000000000459519
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000000075bfd0
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000075bfd4
R13: 00007ffdb1482e3f R14: 00007f33b051c9c0 R15: 000000000075bfd4
Showing all locks held in the system:
1 lock held by khungtaskd/1043:
#0: 000000004a05a158 (rcu_read_lock){....}, at: rcu_lock_acquire+0x4/0x30
include/linux/rcupdate.h:207
1 lock held by rsyslogd/7880:
#0: 00000000946eafbf (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x243/0x2e0
fs/file.c:801
2 locks held by getty/7970:
#0: 00000000837c576c (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 000000008890c3b0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7971:
#0: 00000000b66a4c98 (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 00000000d588511a (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7972:
#0: 00000000881b5f61 (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 00000000343a7af4 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7973:
#0: 000000009862f21e (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 0000000033c60fb7 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7974:
#0: 00000000b1abdc0b (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 0000000040853254 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7975:
#0: 00000000fff02dba (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 0000000036cfe603 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
2 locks held by getty/7976:
#0: 0000000059ae43cb (&tty->ldisc_sem){++++}, at:
tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
#1: 0000000032d54919 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
1 lock held by syz-executor.0/8352:
#0: 0000000049c5e979 (&mm->mmap_sem#2){++++}, at: exit_mm+0xdb/0x630
kernel/exit.c:513
2 locks held by syz-executor.0/8354:
1 lock held by syz-executor.0/8355:
#0: 0000000049c5e979 (&mm->mmap_sem#2){++++}, at: exit_mm+0xdb/0x630
kernel/exit.c:513
=============================================
NMI backtrace for cpu 1
CPU: 1 PID: 1043 Comm: khungtaskd Not tainted 5.2.0-rc6+ #7
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1d8/0x2f8 lib/dump_stack.c:113
nmi_cpu_backtrace+0x89/0x160 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x125/0x230 lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x10/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_all_cpu_backtrace+0x17/0x20 include/linux/nmi.h:146
check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
watchdog+0xbb9/0xbd0 kernel/hung_task.c:289
kthread+0x325/0x350 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 8354 Comm: syz-executor.0 Not tainted 5.2.0-rc6+ #7
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:lock_is_held_type+0x26c/0x2b0 kernel/locking/lockdep.c:4346
Code: c7 c7 90 63 aa 88 e8 43 4a 54 00 48 83 3d 9b d2 4f 07 00 74 56 4c 89
e7 57 9d 0f 1f 44 00 00 89 d8 48 83 c4 28 5b 41 5c 41 5d <41> 5e 41 5f 5d
c3 44 89 e9 80 e1 07 80 c1 03 38 c1 7c a8 4c 89 ef
RSP: 0018:ffff8880a4d87708 EFLAGS: 00000296
RAX: 0000000000000000 RBX: ffff88809f0c6040 RCX: 1ffff110149b0f10
RDX: dffffc0000000000 RSI: ffff88809f0c68e0 RDI: 0000000000000286
RBP: ffff8880a4d87718 R08: ffffffff818fd4ed R09: 0000000000000000
R10: ffffed101155a22f R11: 1ffff1101155a22e R12: 0000000000000000
R13: 1ffff11013e18c0a R14: dffffc0000000000 R15: 1ffff11013e18d17
FS: 00007f33b053d700(0000) GS:ffff8880aea00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000941bd000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
lock_is_held include/linux/lockdep.h:356 [inline]
___might_sleep+0x84/0x530 kernel/sched/core.c:6103
__might_sleep+0x8f/0x100 kernel/sched/core.c:6091
__mutex_lock_common+0xc8/0x2fc0 kernel/locking/mutex.c:909
__mutex_lock kernel/locking/mutex.c:1073 [inline]
mutex_lock_nested+0x1b/0x30 kernel/locking/mutex.c:1088
perf_mmap+0x76d/0x16c0 kernel/events/core.c:5672
call_mmap include/linux/fs.h:1877 [inline]
mmap_region+0x186d/0x1d80 mm/mmap.c:1788
do_mmap+0x9de/0x1010 mm/mmap.c:1561
do_mmap_pgoff include/linux/mm.h:2402 [inline]
vm_mmap_pgoff+0x190/0x240 mm/util.c:363
ksys_mmap_pgoff+0x4ed/0x5f0 mm/mmap.c:1611
__do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
__se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
__x64_sys_mmap+0x103/0x120 arch/x86/kernel/sys_x86_64.c:91
do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459519
Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f33b053cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 0000000000459519
RDX: 0000000000000000 RSI: 0000000000003000 RDI: 0000000020ffd000
RBP: 000000000075bf20 R08: 0000000000000003 R09: 0000000000000000
R10: 0080000000000011 R11: 0000000000000246 R12: 00007f33b053d6d4
R13: 00000000004c5822 R14: 00000000004d9ed8 R15: 00000000ffffffff
---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.
syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: INFO: task hung in exit_mm
2019-07-01 8:27 INFO: task hung in exit_mm syzbot
@ 2019-07-02 0:14 ` Andrew Morton
2019-07-02 9:06 ` Peter Zijlstra
0 siblings, 1 reply; 4+ messages in thread
From: Andrew Morton @ 2019-07-02 0:14 UTC (permalink / raw)
To: syzbot
Cc: aarcange, avagin, davem, ebiederm, linux-kernel, oleg, prsood,
syzkaller-bugs, tj, Peter Zijlstra, Ingo Molnar
On Mon, 01 Jul 2019 01:27:04 -0700 syzbot <syzbot+8cc1843d4eec9c0dfb35@syzkaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
At a guess I'd say that perf_mmap() hit a deadlock on event->mmap_mutex
while holding down_write(mmap_sem) (via vm_mmap_pgoff). The
down_read(mmap_sem) in do_exit() happened to stumble across this and
that's what got reported.
> HEAD commit: 249155c2 Merge branch 'parisc-5.2-4' of git://git.kernel.o..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1306be61a00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=9a31528e58cc12e2
> dashboard link: https://syzkaller.appspot.com/bug?extid=8cc1843d4eec9c0dfb35
> compiler: clang version 9.0.0 (/home/glider/llvm/clang
> 80fee25776c2fb61e74c1ecb1a523375c2500b69)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14a85379a00000
>
> Bisection is inconclusive: the bug happens on the oldest tested release.
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=119f6249a00000
> final crash: https://syzkaller.appspot.com/x/report.txt?x=139f6249a00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=159f6249a00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+8cc1843d4eec9c0dfb35@syzkaller.appspotmail.com
>
> INFO: task syz-executor.0:8352 blocked for more than 143 seconds.
> Not tainted 5.2.0-rc6+ #7
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> syz-executor.0 D24576 8352 8340 0x80004000
> Call Trace:
> context_switch kernel/sched/core.c:2818 [inline]
> __schedule+0x658/0x9e0 kernel/sched/core.c:3445
> schedule+0x131/0x1d0 kernel/sched/core.c:3509
> __rwsem_down_read_failed_common+0x345/0x790 kernel/locking/rwsem-xadd.c:495
> rwsem_down_read_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:515
> __down_read+0x72/0x1a0 kernel/locking/rwsem.h:178
> down_read+0x45/0x50 kernel/locking/rwsem.c:26
> exit_mm+0xdb/0x630 kernel/exit.c:513
> do_exit+0x5c3/0x2300 kernel/exit.c:864
> do_group_exit+0x15c/0x2a0 kernel/exit.c:981
> __do_sys_exit_group+0x17/0x20 kernel/exit.c:992
> __se_sys_exit_group+0x14/0x20 kernel/exit.c:990
> __x64_sys_exit_group+0x3b/0x40 kernel/exit.c:990
> do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:301
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x459519
> Code: Bad RIP value.
> RSP: 002b:00007ffdb1483048 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 000000000000001e RCX: 0000000000459519
> RDX: 0000000000413201 RSI: fffffffffffffff7 RDI: 0000000000000000
> RBP: 0000000000000000 R08: ffffffffffffffff R09: 00007ffdb14830a0
> R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000001
> R13: 00007ffdb14830a0 R14: 0000000000000000 R15: 00007ffdb14830b0
> INFO: task syz-executor.0:8355 blocked for more than 143 seconds.
> Not tainted 5.2.0-rc6+ #7
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> syz-executor.0 D25512 8355 8340 0x80004000
> Call Trace:
> context_switch kernel/sched/core.c:2818 [inline]
> __schedule+0x658/0x9e0 kernel/sched/core.c:3445
> schedule+0x131/0x1d0 kernel/sched/core.c:3509
> __rwsem_down_read_failed_common+0x345/0x790 kernel/locking/rwsem-xadd.c:495
> rwsem_down_read_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:515
> __down_read+0x72/0x1a0 kernel/locking/rwsem.h:178
> down_read+0x45/0x50 kernel/locking/rwsem.c:26
> exit_mm+0xdb/0x630 kernel/exit.c:513
> do_exit+0x5c3/0x2300 kernel/exit.c:864
> do_group_exit+0x15c/0x2a0 kernel/exit.c:981
> get_signal+0x6df/0x21f0 kernel/signal.c:2640
> do_signal+0x7b/0x750 arch/x86/kernel/signal.c:815
> exit_to_usermode_loop arch/x86/entry/common.c:164 [inline]
> prepare_exit_to_usermode+0x2f5/0x4f0 arch/x86/entry/common.c:199
> syscall_return_slowpath+0x110/0x440 arch/x86/entry/common.c:279
> do_syscall_64+0x126/0x140 arch/x86/entry/common.c:304
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x459519
> Code: Bad RIP value.
> RSP: 002b:00007f33b051bcf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
> RAX: fffffffffffffe00 RBX: 000000000075bfd0 RCX: 0000000000459519
> RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000000075bfd0
> RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000075bfd4
> R13: 00007ffdb1482e3f R14: 00007f33b051c9c0 R15: 000000000075bfd4
>
> Showing all locks held in the system:
> 1 lock held by khungtaskd/1043:
> #0: 000000004a05a158 (rcu_read_lock){....}, at: rcu_lock_acquire+0x4/0x30
> include/linux/rcupdate.h:207
> 1 lock held by rsyslogd/7880:
> #0: 00000000946eafbf (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x243/0x2e0
> fs/file.c:801
> 2 locks held by getty/7970:
> #0: 00000000837c576c (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> #1: 000000008890c3b0 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/7971:
> #0: 00000000b66a4c98 (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> #1: 00000000d588511a (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/7972:
> #0: 00000000881b5f61 (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> #1: 00000000343a7af4 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/7973:
> #0: 000000009862f21e (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> #1: 0000000033c60fb7 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/7974:
> #0: 00000000b1abdc0b (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> #1: 0000000040853254 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/7975:
> #0: 00000000fff02dba (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> #1: 0000000036cfe603 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/7976:
> #0: 0000000059ae43cb (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> #1: 0000000032d54919 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 1 lock held by syz-executor.0/8352:
> #0: 0000000049c5e979 (&mm->mmap_sem#2){++++}, at: exit_mm+0xdb/0x630
> kernel/exit.c:513
> 2 locks held by syz-executor.0/8354:
> 1 lock held by syz-executor.0/8355:
> #0: 0000000049c5e979 (&mm->mmap_sem#2){++++}, at: exit_mm+0xdb/0x630
> kernel/exit.c:513
>
> =============================================
>
> NMI backtrace for cpu 1
> CPU: 1 PID: 1043 Comm: khungtaskd Not tainted 5.2.0-rc6+ #7
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x1d8/0x2f8 lib/dump_stack.c:113
> nmi_cpu_backtrace+0x89/0x160 lib/nmi_backtrace.c:101
> nmi_trigger_cpumask_backtrace+0x125/0x230 lib/nmi_backtrace.c:62
> arch_trigger_cpumask_backtrace+0x10/0x20 arch/x86/kernel/apic/hw_nmi.c:38
> trigger_all_cpu_backtrace+0x17/0x20 include/linux/nmi.h:146
> check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
> watchdog+0xbb9/0xbd0 kernel/hung_task.c:289
> kthread+0x325/0x350 kernel/kthread.c:255
> ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> Sending NMI from CPU 1 to CPUs 0:
> NMI backtrace for cpu 0
> CPU: 0 PID: 8354 Comm: syz-executor.0 Not tainted 5.2.0-rc6+ #7
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:lock_is_held_type+0x26c/0x2b0 kernel/locking/lockdep.c:4346
> Code: c7 c7 90 63 aa 88 e8 43 4a 54 00 48 83 3d 9b d2 4f 07 00 74 56 4c 89
> e7 57 9d 0f 1f 44 00 00 89 d8 48 83 c4 28 5b 41 5c 41 5d <41> 5e 41 5f 5d
> c3 44 89 e9 80 e1 07 80 c1 03 38 c1 7c a8 4c 89 ef
> RSP: 0018:ffff8880a4d87708 EFLAGS: 00000296
> RAX: 0000000000000000 RBX: ffff88809f0c6040 RCX: 1ffff110149b0f10
> RDX: dffffc0000000000 RSI: ffff88809f0c68e0 RDI: 0000000000000286
> RBP: ffff8880a4d87718 R08: ffffffff818fd4ed R09: 0000000000000000
> R10: ffffed101155a22f R11: 1ffff1101155a22e R12: 0000000000000000
> R13: 1ffff11013e18c0a R14: dffffc0000000000 R15: 1ffff11013e18d17
> FS: 00007f33b053d700(0000) GS:ffff8880aea00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000000 CR3: 00000000941bd000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> lock_is_held include/linux/lockdep.h:356 [inline]
> ___might_sleep+0x84/0x530 kernel/sched/core.c:6103
> __might_sleep+0x8f/0x100 kernel/sched/core.c:6091
> __mutex_lock_common+0xc8/0x2fc0 kernel/locking/mutex.c:909
> __mutex_lock kernel/locking/mutex.c:1073 [inline]
> mutex_lock_nested+0x1b/0x30 kernel/locking/mutex.c:1088
> perf_mmap+0x76d/0x16c0 kernel/events/core.c:5672
> call_mmap include/linux/fs.h:1877 [inline]
> mmap_region+0x186d/0x1d80 mm/mmap.c:1788
> do_mmap+0x9de/0x1010 mm/mmap.c:1561
> do_mmap_pgoff include/linux/mm.h:2402 [inline]
> vm_mmap_pgoff+0x190/0x240 mm/util.c:363
> ksys_mmap_pgoff+0x4ed/0x5f0 mm/mmap.c:1611
> __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
> __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
> __x64_sys_mmap+0x103/0x120 arch/x86/kernel/sys_x86_64.c:91
> do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:301
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x459519
> Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
> 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
> ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f33b053cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
> RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 0000000000459519
> RDX: 0000000000000000 RSI: 0000000000003000 RDI: 0000000020ffd000
> RBP: 000000000075bf20 R08: 0000000000000003 R09: 0000000000000000
> R10: 0080000000000011 R11: 0000000000000246 R12: 00007f33b053d6d4
> R13: 00000000004c5822 R14: 00000000004d9ed8 R15: 00000000ffffffff
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: INFO: task hung in exit_mm
2019-07-02 0:14 ` Andrew Morton
@ 2019-07-02 9:06 ` Peter Zijlstra
2019-07-02 9:36 ` Peter Zijlstra
0 siblings, 1 reply; 4+ messages in thread
From: Peter Zijlstra @ 2019-07-02 9:06 UTC (permalink / raw)
To: Andrew Morton
Cc: syzbot, aarcange, avagin, davem, ebiederm, linux-kernel, oleg,
prsood, syzkaller-bugs, tj, Ingo Molnar
On Mon, Jul 01, 2019 at 05:14:12PM -0700, Andrew Morton wrote:
> On Mon, 01 Jul 2019 01:27:04 -0700 syzbot <syzbot+8cc1843d4eec9c0dfb35@syzkaller.appspotmail.com> wrote:
>
> > Hello,
> >
> > syzbot found the following crash on:
>
> At a guess I'd say that perf_mmap() hit a deadlock on event->mmap_mutex
> while holding down_write(mmap_sem) (via vm_mmap_pgoff). The
> down_read(mmap_sem) in do_exit() happened to stumble across this and
> that's what got reported.
lockdep never reported that and I don't see event->mmap_mutex being held
anywhere.
AFAICT CPU0 is running 8355 and only 'has' mmap_sem -- it's blocked
waiting to acquire.
CPU1 is running 8354 and has mmap_sem and is waiting to acquire
event->mmap_mutex.
But nobody is actually owning it
We take mmap_mutex in:
perf_mmap() - called with mmap_sem held
perf_mmap_close() - called with mmap_sem held
_free_event() - no faults/mmap while holding it
perf_poll() - idem
perf_event_set_output() - idem
I don't see any of those functions in the below stacktrace, and having
just looked them over, I don't see how they would end up trying to
acquire mmap_sem and AB-BA.
Now, clearly there's something screwy, but I'm not seeing a deadlock.
Let me go play with that reproducer.
> > HEAD commit: 249155c2 Merge branch 'parisc-5.2-4' of git://git.kernel.o..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1306be61a00000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=9a31528e58cc12e2
> > dashboard link: https://syzkaller.appspot.com/bug?extid=8cc1843d4eec9c0dfb35
> > compiler: clang version 9.0.0 (/home/glider/llvm/clang
> > 80fee25776c2fb61e74c1ecb1a523375c2500b69)
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14a85379a00000
> >
> > Bisection is inconclusive: the bug happens on the oldest tested release.
> >
> > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=119f6249a00000
> > final crash: https://syzkaller.appspot.com/x/report.txt?x=139f6249a00000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=159f6249a00000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+8cc1843d4eec9c0dfb35@syzkaller.appspotmail.com
> >
> > INFO: task syz-executor.0:8352 blocked for more than 143 seconds.
> > Not tainted 5.2.0-rc6+ #7
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > syz-executor.0 D24576 8352 8340 0x80004000
> > Call Trace:
> > context_switch kernel/sched/core.c:2818 [inline]
> > __schedule+0x658/0x9e0 kernel/sched/core.c:3445
> > schedule+0x131/0x1d0 kernel/sched/core.c:3509
> > __rwsem_down_read_failed_common+0x345/0x790 kernel/locking/rwsem-xadd.c:495
> > rwsem_down_read_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:515
> > __down_read+0x72/0x1a0 kernel/locking/rwsem.h:178
> > down_read+0x45/0x50 kernel/locking/rwsem.c:26
> > exit_mm+0xdb/0x630 kernel/exit.c:513
> > do_exit+0x5c3/0x2300 kernel/exit.c:864
> > do_group_exit+0x15c/0x2a0 kernel/exit.c:981
> > __do_sys_exit_group+0x17/0x20 kernel/exit.c:992
> > __se_sys_exit_group+0x14/0x20 kernel/exit.c:990
> > __x64_sys_exit_group+0x3b/0x40 kernel/exit.c:990
> > do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:301
> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > RIP: 0033:0x459519
> > Code: Bad RIP value.
> > RSP: 002b:00007ffdb1483048 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> > RAX: ffffffffffffffda RBX: 000000000000001e RCX: 0000000000459519
> > RDX: 0000000000413201 RSI: fffffffffffffff7 RDI: 0000000000000000
> > RBP: 0000000000000000 R08: ffffffffffffffff R09: 00007ffdb14830a0
> > R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000001
> > R13: 00007ffdb14830a0 R14: 0000000000000000 R15: 00007ffdb14830b0
> > INFO: task syz-executor.0:8355 blocked for more than 143 seconds.
> > Not tainted 5.2.0-rc6+ #7
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > syz-executor.0 D25512 8355 8340 0x80004000
> > Call Trace:
> > context_switch kernel/sched/core.c:2818 [inline]
> > __schedule+0x658/0x9e0 kernel/sched/core.c:3445
> > schedule+0x131/0x1d0 kernel/sched/core.c:3509
> > __rwsem_down_read_failed_common+0x345/0x790 kernel/locking/rwsem-xadd.c:495
> > rwsem_down_read_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:515
> > __down_read+0x72/0x1a0 kernel/locking/rwsem.h:178
> > down_read+0x45/0x50 kernel/locking/rwsem.c:26
> > exit_mm+0xdb/0x630 kernel/exit.c:513
> > do_exit+0x5c3/0x2300 kernel/exit.c:864
> > do_group_exit+0x15c/0x2a0 kernel/exit.c:981
> > get_signal+0x6df/0x21f0 kernel/signal.c:2640
> > do_signal+0x7b/0x750 arch/x86/kernel/signal.c:815
> > exit_to_usermode_loop arch/x86/entry/common.c:164 [inline]
> > prepare_exit_to_usermode+0x2f5/0x4f0 arch/x86/entry/common.c:199
> > syscall_return_slowpath+0x110/0x440 arch/x86/entry/common.c:279
> > do_syscall_64+0x126/0x140 arch/x86/entry/common.c:304
> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > RIP: 0033:0x459519
> > Code: Bad RIP value.
> > RSP: 002b:00007f33b051bcf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
> > RAX: fffffffffffffe00 RBX: 000000000075bfd0 RCX: 0000000000459519
> > RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000000075bfd0
> > RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 000000000075bfd4
> > R13: 00007ffdb1482e3f R14: 00007f33b051c9c0 R15: 000000000075bfd4
> >
> > Showing all locks held in the system:
> > 1 lock held by khungtaskd/1043:
> > #0: 000000004a05a158 (rcu_read_lock){....}, at: rcu_lock_acquire+0x4/0x30
> > include/linux/rcupdate.h:207
> > 1 lock held by rsyslogd/7880:
> > #0: 00000000946eafbf (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x243/0x2e0
> > fs/file.c:801
> > 2 locks held by getty/7970:
> > #0: 00000000837c576c (&tty->ldisc_sem){++++}, at:
> > tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> > #1: 000000008890c3b0 (&ldata->atomic_read_lock){+.+.}, at:
> > n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> > 2 locks held by getty/7971:
> > #0: 00000000b66a4c98 (&tty->ldisc_sem){++++}, at:
> > tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> > #1: 00000000d588511a (&ldata->atomic_read_lock){+.+.}, at:
> > n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> > 2 locks held by getty/7972:
> > #0: 00000000881b5f61 (&tty->ldisc_sem){++++}, at:
> > tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> > #1: 00000000343a7af4 (&ldata->atomic_read_lock){+.+.}, at:
> > n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> > 2 locks held by getty/7973:
> > #0: 000000009862f21e (&tty->ldisc_sem){++++}, at:
> > tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> > #1: 0000000033c60fb7 (&ldata->atomic_read_lock){+.+.}, at:
> > n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> > 2 locks held by getty/7974:
> > #0: 00000000b1abdc0b (&tty->ldisc_sem){++++}, at:
> > tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> > #1: 0000000040853254 (&ldata->atomic_read_lock){+.+.}, at:
> > n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> > 2 locks held by getty/7975:
> > #0: 00000000fff02dba (&tty->ldisc_sem){++++}, at:
> > tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> > #1: 0000000036cfe603 (&ldata->atomic_read_lock){+.+.}, at:
> > n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> > 2 locks held by getty/7976:
> > #0: 0000000059ae43cb (&tty->ldisc_sem){++++}, at:
> > tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
> > #1: 0000000032d54919 (&ldata->atomic_read_lock){+.+.}, at:
> > n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> > 1 lock held by syz-executor.0/8352:
> > #0: 0000000049c5e979 (&mm->mmap_sem#2){++++}, at: exit_mm+0xdb/0x630
> > kernel/exit.c:513
> > 2 locks held by syz-executor.0/8354:
> > 1 lock held by syz-executor.0/8355:
> > #0: 0000000049c5e979 (&mm->mmap_sem#2){++++}, at: exit_mm+0xdb/0x630
> > kernel/exit.c:513
> >
> > =============================================
> >
> > NMI backtrace for cpu 1
> > CPU: 1 PID: 1043 Comm: khungtaskd Not tainted 5.2.0-rc6+ #7
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > Call Trace:
> > __dump_stack lib/dump_stack.c:77 [inline]
> > dump_stack+0x1d8/0x2f8 lib/dump_stack.c:113
> > nmi_cpu_backtrace+0x89/0x160 lib/nmi_backtrace.c:101
> > nmi_trigger_cpumask_backtrace+0x125/0x230 lib/nmi_backtrace.c:62
> > arch_trigger_cpumask_backtrace+0x10/0x20 arch/x86/kernel/apic/hw_nmi.c:38
> > trigger_all_cpu_backtrace+0x17/0x20 include/linux/nmi.h:146
> > check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
> > watchdog+0xbb9/0xbd0 kernel/hung_task.c:289
> > kthread+0x325/0x350 kernel/kthread.c:255
> > ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> > Sending NMI from CPU 1 to CPUs 0:
> > NMI backtrace for cpu 0
> > CPU: 0 PID: 8354 Comm: syz-executor.0 Not tainted 5.2.0-rc6+ #7
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > RIP: 0010:lock_is_held_type+0x26c/0x2b0 kernel/locking/lockdep.c:4346
> > Code: c7 c7 90 63 aa 88 e8 43 4a 54 00 48 83 3d 9b d2 4f 07 00 74 56 4c 89
> > e7 57 9d 0f 1f 44 00 00 89 d8 48 83 c4 28 5b 41 5c 41 5d <41> 5e 41 5f 5d
> > c3 44 89 e9 80 e1 07 80 c1 03 38 c1 7c a8 4c 89 ef
> > RSP: 0018:ffff8880a4d87708 EFLAGS: 00000296
> > RAX: 0000000000000000 RBX: ffff88809f0c6040 RCX: 1ffff110149b0f10
> > RDX: dffffc0000000000 RSI: ffff88809f0c68e0 RDI: 0000000000000286
> > RBP: ffff8880a4d87718 R08: ffffffff818fd4ed R09: 0000000000000000
> > R10: ffffed101155a22f R11: 1ffff1101155a22e R12: 0000000000000000
> > R13: 1ffff11013e18c0a R14: dffffc0000000000 R15: 1ffff11013e18d17
> > FS: 00007f33b053d700(0000) GS:ffff8880aea00000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000000000000 CR3: 00000000941bd000 CR4: 00000000001406f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> > lock_is_held include/linux/lockdep.h:356 [inline]
> > ___might_sleep+0x84/0x530 kernel/sched/core.c:6103
> > __might_sleep+0x8f/0x100 kernel/sched/core.c:6091
> > __mutex_lock_common+0xc8/0x2fc0 kernel/locking/mutex.c:909
> > __mutex_lock kernel/locking/mutex.c:1073 [inline]
> > mutex_lock_nested+0x1b/0x30 kernel/locking/mutex.c:1088
> > perf_mmap+0x76d/0x16c0 kernel/events/core.c:5672
> > call_mmap include/linux/fs.h:1877 [inline]
> > mmap_region+0x186d/0x1d80 mm/mmap.c:1788
> > do_mmap+0x9de/0x1010 mm/mmap.c:1561
> > do_mmap_pgoff include/linux/mm.h:2402 [inline]
> > vm_mmap_pgoff+0x190/0x240 mm/util.c:363
> > ksys_mmap_pgoff+0x4ed/0x5f0 mm/mmap.c:1611
> > __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
> > __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
> > __x64_sys_mmap+0x103/0x120 arch/x86/kernel/sys_x86_64.c:91
> > do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:301
> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > RIP: 0033:0x459519
> > Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
> > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
> > ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> > RSP: 002b:00007f33b053cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
> > RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 0000000000459519
> > RDX: 0000000000000000 RSI: 0000000000003000 RDI: 0000000020ffd000
> > RBP: 000000000075bf20 R08: 0000000000000003 R09: 0000000000000000
> > R10: 0080000000000011 R11: 0000000000000246 R12: 00007f33b053d6d4
> > R13: 00000000004c5822 R14: 00000000004d9ed8 R15: 00000000ffffffff
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: INFO: task hung in exit_mm
2019-07-02 9:06 ` Peter Zijlstra
@ 2019-07-02 9:36 ` Peter Zijlstra
0 siblings, 0 replies; 4+ messages in thread
From: Peter Zijlstra @ 2019-07-02 9:36 UTC (permalink / raw)
To: Andrew Morton
Cc: syzbot, aarcange, avagin, davem, ebiederm, linux-kernel, oleg,
prsood, syzkaller-bugs, tj, Ingo Molnar
On Tue, Jul 02, 2019 at 11:06:08AM +0200, Peter Zijlstra wrote:
> On Mon, Jul 01, 2019 at 05:14:12PM -0700, Andrew Morton wrote:
> > On Mon, 01 Jul 2019 01:27:04 -0700 syzbot <syzbot+8cc1843d4eec9c0dfb35@syzkaller.appspotmail.com> wrote:
> >
> > > Hello,
> > >
> > > syzbot found the following crash on:
> >
> > At a guess I'd say that perf_mmap() hit a deadlock on event->mmap_mutex
> > while holding down_write(mmap_sem) (via vm_mmap_pgoff). The
> > down_read(mmap_sem) in do_exit() happened to stumble across this and
> > that's what got reported.
>
> lockdep never reported that and I don't see event->mmap_mutex being held
> anywhere.
>
> AFAICT CPU0 is running 8355 and only 'has' mmap_sem -- it's blocked
> waiting to acquire.
>
> CPU1 is running 8354 and has mmap_sem and is waiting to acquire
> event->mmap_mutex.
>
> But nobody is actually owning it
>
> We take mmap_mutex in:
>
> perf_mmap() - called with mmap_sem held
> perf_mmap_close() - called with mmap_sem held
>
> _free_event() - no faults/mmap while holding it
> perf_poll() - idem
> perf_event_set_output() - idem
>
> I don't see any of those functions in the below stacktrace, and having
> just looked them over, I don't see how they would end up trying to
> acquire mmap_sem and AB-BA.
>
> Now, clearly there's something screwy, but I'm not seeing a deadlock.
> Let me go play with that reproducer.
>
> > > HEAD commit: 249155c2 Merge branch 'parisc-5.2-4' of git://git.kernel.o..
> > > git tree: upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=1306be61a00000
> > > kernel config: https://syzkaller.appspot.com/x/.config?x=9a31528e58cc12e2
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=8cc1843d4eec9c0dfb35
> > > compiler: clang version 9.0.0 (/home/glider/llvm/clang
Also note that I very much do not trust that compiler to build a working
kernel. There's still known code-gen bugs with it.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-07-02 9:36 UTC | newest]
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2019-07-01 8:27 INFO: task hung in exit_mm syzbot
2019-07-02 0:14 ` Andrew Morton
2019-07-02 9:06 ` Peter Zijlstra
2019-07-02 9:36 ` Peter Zijlstra
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