[-Bcc wrongly added folks] [+Cc kernel/time maintainers] On Mon, Aug 31, 2020 at 10:07AM -0700, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 1127b219 Merge tag 'fallthrough-fixes-5.9-rc3' of git://gi.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=1501768e900000 > kernel config: https://syzkaller.appspot.com/x/.config?x=978db74cb30aa994 > dashboard link: https://syzkaller.appspot.com/bug?extid=3b14b2ed9b3d06dcaa07 Dashboard has recent reports (also below) and reproducer (also attached). > compiler: gcc (GCC) 10.1.0-syz 20200507 > userspace arch: i386 Not just i386. > The issue was bisected to: > > commit b1012ca8dc4f9b1a1fe8e2cb1590dd6d43ea3849 > Author: Lu Baolu > Date: Thu Jul 23 01:34:37 2020 +0000 > > iommu/vt-d: Skip TE disabling on quirky gfx dedicated iommu This bisection is wrong. > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+3b14b2ed9b3d06dcaa07@syzkaller.appspotmail.com [...] > WARNING: CPU: 0 PID: 10581 at kernel/time/posix-timers.c:849 timer_wait_running+0x218/0x250 kernel/time/posix-timers.c:849 [ .. snip ancient warning ..] Up-to-date warning: | WARNING: CPU: 1 PID: 6695 at kernel/time/posix-timers.c:849 timer_wait_running+0x255/0x290 kernel/time/posix-timers.c:849 | Modules linked in: | CPU: 1 PID: 6695 Comm: syz-executor.3 Not tainted 6.3.0-rc3-syzkaller-00338-gda8e7da11e4b #0 | Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023 | RIP: 0010:timer_wait_running+0x255/0x290 kernel/time/posix-timers.c:849 | Code: 00 48 c7 c2 80 fe 4e 8a be 06 03 00 00 48 c7 c7 e0 fe 4e 8a c6 05 63 cb ed 0c 01 e8 85 77 ef ff e9 5b fe ff ff e8 2b 7d 0e 00 <0f> 0b e9 b2 fe ff ff e8 0f 8a 5f 00 e9 fe fd ff ff e8 25 8a 5f 00 | RSP: 0018:ffffc90003ecfd50 EFLAGS: 00010293 | RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 | RDX: ffff888020e4ba80 RSI: ffffffff81746785 RDI: ffffffff8a4f0ad8 | RBP: ffff88807c696d38 R08: 0000000000000001 R09: 0000000000000001 | R10: fffffbfff1cef98a R11: 0000000000000021 R12: ffffc90003ecfdb0 | R13: 0000000000000000 R14: ffffffff8a4f0a60 R15: ffffc90003ecfdb0 | FS: 00007fae387fe700(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000 | CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 | CR2: 00007f0d105821b8 CR3: 000000002a283000 CR4: 00000000003526e0 | DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 | DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 | Call Trace: | | do_timer_settime.part.0+0x119/0x1d0 kernel/time/posix-timers.c:929 | do_timer_settime kernel/time/posix-timers.c:938 [inline] | __do_sys_timer_settime kernel/time/posix-timers.c:952 [inline] | __se_sys_timer_settime kernel/time/posix-timers.c:938 [inline] | __x64_sys_timer_settime+0x21d/0x310 kernel/time/posix-timers.c:938 | do_syscall_x64 arch/x86/entry/common.c:50 [inline] | do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 | entry_SYSCALL_64_after_hwframe+0x63/0xcd | RIP: 0033:0x7fae3948c0f9 | Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 | RSP: 002b:00007fae387fe168 EFLAGS: 00000246 ORIG_RAX: 00000000000000df | RAX: ffffffffffffffda RBX: 00007fae395ac050 RCX: 00007fae3948c0f9 | RDX: 0000000020000080 RSI: 0000000000000000 RDI: 0000000000000000 | RBP: 00007fae394e7b39 R08: 0000000000000000 R09: 0000000000000000 | R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 | R13: 00007fae396cfb1f R14: 00007fae387fe300 R15: 0000000000022000 | I've seen this warning in the wild recently, and it's been around since 2020 according to syzbot. The warning was added in ec8f954a40da8 ("posix-timers: Use a callback for cancel synchronization on PREEMPT_RT"). Why is it wrong for timer_wait_running to be NULL? [ attached C reproducer ] Thanks, -- Marco