On 01/25/2012 09:01 PM, Srivatsa S. Bhat wrote:
> On 01/25/2012 05:40 AM, Rafael J. Wysocki wrote:
>
>> On Wednesday, January 25, 2012, Jiri Slaby wrote:
>>> On 01/25/2012 12:02 AM, Rafael J. Wysocki wrote:
>>>> On Tuesday, January 24, 2012, Jiri Slaby wrote:
>>>>> On 01/24/2012 11:36 PM, Rafael J. Wysocki wrote:
>>>>>> On Tuesday, January 24, 2012, Jiri Slaby wrote:
>>>>>>> On 01/24/2012 05:18 PM, Srivatsa S. Bhat wrote:
>>>>>>>> Hi Jiri,
>>>>>>>>
>>>>>>>> On 01/24/2012 08:35 PM, Jiri Slaby wrote:
>>>>>>>>
>>>>>>>>> Hi,
>>>>>>>>>
>>>>>>>>> this is a freshly booted system. When I do s2dsk, I see:
>>>>>>>>> ...
>>>>>>>>> Freezing remaining freezable tasks ... BUG: 'workqueue_freezing' is true!
>>>>>>>>> ------------[ cut here ]------------
>>>>>>>>> kernel BUG at /l/latest/linux/kernel/workqueue.c:3659!
>>>>>>>>> invalid opcode: 0000 [#1] SMP
>>>>>>>>> CPU 0
>>>>>>>>> Modules linked in:
>>>>>>>>>
>>>>>>>>> Pid: 2669, comm: s2disk Not tainted 3.3.0-rc1-next-20120124_64+ #1627
>>>>>>>>> Bochs Bochs
>>>>>>>>> RIP: 0010:[<ffffffff8107e365>] [<ffffffff8107e365>]
>>>>>>>>> freeze_workqueues_begin+0x195/0x1a0
>>>>>>>>> RSP: 0018:ffff880046f01d68 EFLAGS: 00010292
>>>>>>>>> RAX: 0000000000000023 RBX: 0000000000000001 RCX: 00000000000000c9
>>>>>>>>> RDX: 0000000000000077 RSI: 0000000000000046 RDI: ffffffff81b51f7c
>>>>>>>>> RBP: ffff880046f01d98 R08: ffffffff81a9d760 R09: 0000000000000000
>>>>>>>>> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
>>>>>>>>> R13: 00007fff579464dc R14: ffffffffffffffff R15: 0000000000000004
>>>>>>>>> FS: 00007f3c65d54700(0000) GS:ffff880049600000(0000) knlGS:0000000000000000
>>>>>>>>> CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>>>>>>>> CR2: 00007f3c64f58c20 CR3: 0000000045b64000 CR4: 00000000000006f0
>>>>>>>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>>>>>>>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>>>>>>>>> Process s2disk (pid: 2669, threadinfo ffff880046f00000, task
>>>>>>>>> ffff880047251980)
>>>>>>>>> Stack:
>>>>>>>>> ffff880046f01d98 0000000000000001 0000000000000000 00007fff579464dc
>>>>>>>>> ffffffffffffffff 0000000000000004 ffff880046f01e18 ffffffff81096cb9
>>>>>>>>> 00000000ffff0124 0000000000000004 ffff880046f01e18 000000004f1ec7d1
>>>>>>>>> Call Trace:
>>>>>>>>> [<ffffffff81096cb9>] try_to_freeze_tasks+0x1b9/0x2d0
>>>>>>>>> [<ffffffff81096ed5>] freeze_kernel_threads+0x25/0x90
>>>>>>>>> [<ffffffff81097b55>] hibernation_snapshot+0x75/0x2e0
>>>>>>>>> [<ffffffff8109d724>] snapshot_ioctl+0x314/0x4e0
>>>>>>>>> [<ffffffff81130856>] do_vfs_ioctl+0x96/0x550
>>>>>>>>> [<ffffffff8111ff7b>] ? vfs_write+0x10b/0x180
>>>>>>>>> [<ffffffff81130d5a>] sys_ioctl+0x4a/0x80
>>>>>>>>> [<ffffffff81630e22>] system_call_fastpath+0x16/0x1b
>>>>>>>>> Code: c7 c6 0a a4 92 81 48 c7 c7 16 65 92 81 31 c0 e8 19 94 5a 00 0f 0b
>>>>>>>>> 48 c7 c6 27 a4 92 81 48 c7 c7 16 65 92 81 31 c0 e8 02 94 5a 00 <0f> 0b
>>>>>>>>> 66 0f 1f 84 00 00 00 00 00 55 48 c7 c7 82 4b b9 81 48 89
>>>>>>>>> RIP [<ffffffff8107e365>] freeze_workqueues_begin+0x195/0x1a0
>>>>>>>>> RSP <ffff880046f01d68>
>>>>>>>>> ---[ end trace 632574abdc098963 ]---
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> I couldn't find any obvious root-cause from a quick check. Is this completely
>>>>>>>> reproducible upon a fresh boot?
>>>>>>>
>>>>>>> True.
>>>>>>>
>>>>>>> The cause is that the function is called twice:
>>>>>>
>>>>>> Which function?
>>>>>
>>>>> The one where the BUG is. Maybe the functions which should clear the
>>>>> flag is not called in between? See:
>>>>>
>>>>>>> [<ffffffff8107e206>] freeze_workqueues_begin+0x36/0x1b0
>>>>> ^^^^^^^^^^^^^^^^^^^^^^^
>>>>>>> [<ffffffff81096cc9>] try_to_freeze_tasks+0x1b9/0x2d0
>>>>>>> [<ffffffff81096ee5>] freeze_kernel_threads+0x25/0x90
>>>>>>> [<ffffffff81097b65>] hibernation_snapshot+0x75/0x2e0
>>>>>>> [<ffffffff8109d734>] snapshot_ioctl+0x314/0x4e0
>>>>>>> [<ffffffff81130866>] do_vfs_ioctl+0x96/0x550
>>>>>>> [<ffffffff8111ff8b>] ? vfs_write+0x10b/0x180
>>>>>>> [<ffffffff81130d6a>] sys_ioctl+0x4a/0x80
>>>>>>> [<ffffffff81630e22>] system_call_fastpath+0x16/0x1b
>>>>>>> (elapsed 0.03 seconds) done.
>>>>> ...
>>>>>>> Freezing remaining freezable tasks ... BUG: 'workqueue_freezing' is true!
>>>>>>> ------------[ cut here ]------------
>>>>>>> kernel BUG at /l/latest/linux/kernel/workqueue.c:3659!
>>>>> ...
>>>>>>> RIP: 0010:[<ffffffff8107e371>] [<ffffffff8107e371>
>>>>>>> freeze_workqueues_begin+0x1a1/0x1b0
>>>>> ^^^^^^^^^^^^^^^^^^^^^^^
>>>>>>> Call Trace:
>>>>>>> [<ffffffff81096cc9>] try_to_freeze_tasks+0x1b9/0x2d0
>>>>>>> [<ffffffff81096ee5>] freeze_kernel_threads+0x25/0x90
>>>>>>> [<ffffffff81097b65>] hibernation_snapshot+0x75/0x2e0
>>>>>>> [<ffffffff8109d734>] snapshot_ioctl+0x314/0x4e0
>>>>>>> [<ffffffff81130866>] do_vfs_ioctl+0x96/0x550
>>>>>>> [<ffffffff8111ff8b>] ? vfs_write+0x10b/0x180
>>>>>>> [<ffffffff81130d6a>] sys_ioctl+0x4a/0x80
>>>>>>> [<ffffffff81630e22>] system_call_fastpath+0x16/0x1b
>>>>
>>>> Ah. So this is linux-next, right?
>>>
>>> Right.
>>>
>>>> Can you please test the linux-next branch of the linux-pm tree and see if
>>>> the problem is reproducible in there?
>>>
>>> Yeah, 100%. Just try it with a small enough swap.
>>
>> Ah, thanks, so that's an error code path problem and most likely in the Linus'
>> tree.
>>
>> Srivatsa, any ideas?
>>
>
>
> Ok, I will need to quote a part of the userspace utility to explain the
> problem.
>
Commit 2aede851 (PM / Hibernate: Freeze kernel threads after preallocating
memory) split up the freezing phase and moved the freezing of kernel threads
to hibernation_snapshot() function.
(This is a pretty old commit btw, I think it came in sometime around 3.2).
And there is a BUG_ON() in freeze_workqueues_begin() which complains if
this function is called when the kernel threads are already frozen.
Now, coming to the userspace utility:
> In suspend.c inside the suspend-utils userspace package, I see a loop such
> as:
>
> error = freeze(snapshot_fd);
> ...
> attempts = 2;
> do {
> if (set_image_size(snapshot_fd, image_size)) {
> error = errno;
> break;
> }
> if (atomic_snapshot(snapshot_fd, &in_suspend)) {
^^^
This ends up in the call to hibernation_snapshot().
> error = errno;
> break;
> }
> if (!in_suspend) {
> /* first unblank the console, see console_codes(4) */
> printf("\e[13]");
> printf("%s: returned to userspace\n", my_name);
> free_snapshot(snapshot_fd);
> break;
> }
>
> error = write_image(snapshot_fd, resume_fd, -1);
> if (error) {
Since swap space is limited, we come here.
> free_swap_pages(snapshot_fd);
> free_snapshot(snapshot_fd);
> image_size = 0;
> error = -error;
> if (error != ENOSPC)
> break;
And because of the above 'if' condition, we don't break here.
IOW, we will run the loop a second time.
> } else {
> splash.progress(100);
> #ifdef CONFIG_BOTH
> if (s2ram_kms || s2ram) {
> /* If we die (and allow system to continue)
> * between now and reset_signature(), very bad
> * things will happen. */
> error = suspend_to_ram(snapshot_fd);
> if (error)
> goto Shutdown;
> reset_signature(resume_fd);
> free_swap_pages(snapshot_fd);
> free_snapshot(snapshot_fd);
> if (!s2ram_kms)
> s2ram_resume();
> goto Unfreeze;
> }
> Shutdown:
> #endif
> close(resume_fd);
> suspend_shutdown(snapshot_fd);
> }
> } while (--attempts);
>
> ...
> Unfreeze:
> unfreeze(snapshot_fd);
>
>
So, since the loop is run a second time if not enough space was available,
we end up calling hibernation_snapshot(), IOW freeze_workqueues_begin() a
second time - and this is what makes the BUG_ON() to fire!
To solve this, I feel we can simply omit the BUG_ON() inside
freeze_workqueues_begin() and replace it with a simple check (just like
what we do in thaw_workqueues())...
And moreover, after the change that moved the freezing of kernel threads
to hibernation_snapshot(), it is quite natural to hit a scenario such
as this, because the entire freezing phase is not in one single place.
IOW, the existing BUG_ON() is not qualified to be there anymore!
(Also, exposing a straight-forward method like this to userspace, to
trigger a BUG_ON sounds ridiculous to start with!)
Of course, the other method would be to refactor the kernel code and stuff
like that, but that not only would be messy but it would also involve
breaking existing userspace applications, AFAICS.
So, Jiri, can you please try the following patch and see if it works for
you as expected? I'll be happy to provide a formal patch with a changelog
if this works.
---
kernel/workqueue.c | 5 ++++-
1 files changed, 4 insertions(+), 1 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index bec7b5b..cb26c5d 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3656,7 +3656,9 @@ void freeze_workqueues_begin(void)
spin_lock(&workqueue_lock);
- BUG_ON(workqueue_freezing);
+ if (workqueue_freezing)
+ goto out_unlock;
+
workqueue_freezing = true;
for_each_gcwq_cpu(cpu) {
@@ -3678,6 +3680,7 @@ void freeze_workqueues_begin(void)
spin_unlock_irq(&gcwq->lock);
}
+out_unlock:
spin_unlock(&workqueue_lock);
}
--
1.7.6
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