On Fri, Jun 28, 2019 at 09:49:03PM -0400, Steven Rostedt wrote: > On Fri, 10 May 2019 12:33:18 +0200 > Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > > > On 2019-05-09 14:33:20 [-0500], minyard@xxxxxxx wrote: > > > From: Corey Minyard <cminyard@xxxxxxxxxx> > > > > > > The function call do_wait_for_common() has a race condition that > > > can result in lockups waiting for completions. Adding the thread > > > to (and removing the thread from) the wait queue for the completion > > > is done outside the do loop in that function. However, if the thread > > > is woken up, the swake_up_locked() function will delete the entry > > > from the wait queue. If that happens and another thread sneaks > > > in and decrements the done count in the completion to zero, the > > > loop will go around again, but the thread will no longer be in the > > > wait queue, so there is no way to wake it up. > > > > applied, thank you. > > > > When I applied this patch to 4.19-rt, I get the following lock up: I was unable to reproduce, and I looked at the code and I can't really see a connection between this change and this crash. Can you reproduce at will? If so, can you send a testcase? -corey > > watchdog: BUG: soft lockup - CPU#2 stuck for 22s! [sh:745] > Modules linked in: floppy i915 drm_kms_helper drm fb_sys_fops sysimgblt sysfillrect syscopyarea iosf_mbi i2c_algo_bit video > CPU: 2 PID: 745 Comm: sh Not tainted 4.19.56-test-rt23+ #16 > Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To be filled by O.E.M., BIOS SDBLI944.86P 05/08/2007 > RIP: 0010:_raw_spin_unlock_irq+0x17/0x4d > Code: 48 8b 12 0f ba e2 12 73 07 e8 f1 4a 92 ff 31 c0 5b 5d c3 66 66 66 66 90 55 48 89 e5 c6 07 00 e8 de 3d a3 ff fb bf 01 00 00 00 <e8> a7 27 9a ff 65 8b 05 c8 7f 93 7e 85 c0 74 1f a9 ff ff > ff 7f 75 > RSP: 0018:ffffc90000c8bbb8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13 > RAX: 0000000000000000 RBX: ffffc90000c8bd58 RCX: 0000000000000003 > RDX: 0000000000000000 RSI: ffffffff8108ffab RDI: 0000000000000001 > RBP: ffffc90000c8bbb8 R08: ffffffff816dcd76 R09: 0000000000020600 > R10: 0000000000000400 R11: 0000001c0eef1808 R12: ffffc90000c8bbc8 > R13: ffffc90000f13ca0 R14: ffff888074b2d7d8 R15: ffff8880789efe10 > FS: 0000000000000000(0000) GS:ffff88807b300000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00000030662001b8 CR3: 00000000376ac000 CR4: 00000000000006e0 > Call Trace: > swake_up_all+0xa6/0xde > __d_lookup_done+0x7c/0xc7 > __d_add+0x44/0xf7 > d_splice_alias+0x208/0x218 > ext4_lookup+0x1a6/0x1c5 > path_openat+0x63a/0xb15 > ? preempt_latency_stop+0x25/0x27 > do_filp_open+0x51/0xae > ? trace_preempt_on+0xde/0xe7 > ? rt_spin_unlock+0x13/0x24 > ? __alloc_fd+0x145/0x155 > do_sys_open+0x81/0x125 > __x64_sys_open+0x21/0x23 > do_syscall_64+0x5c/0x6e > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > I haven't really looked too much into it though. I ran out of time :-/ > > -- Steve
