[PATCH] bdi: Fix oops in wb_workfn()
Syzbot has reported that it can hit a NULL pointer dereference in wb_workfn() due to wb->bdi->dev being NULL. This indicates that wb_workfn() was called for an already unregistered bdi which should not happen as wb_shutdown() called from bdi_unregister() should make sure all pending writeback works are completed before bdi is unregistered. Except that wb_workfn() itself can requeue the work with: mod_delayed_work(bdi_wq, &wb->dwork, 0); and if this happens while wb_shutdown() is waiting in: flush_delayed_work(&wb->dwork); the dwork can get executed after wb_shutdown() has finished and bdi_unregister() has cleared wb->bdi->dev. Make wb_workfn() use wakeup_wb() for requeueing the work which takes all the necessary precautions against racing with bdi unregistration. CC: Tetsuo Handa CC: Tejun Heo Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977 Reported-by: syzbot Signed-off-by: Jan Kara --- fs/fs-writeback.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 47d7c151fcba..471d863958bc 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1961,7 +1961,7 @@ void wb_workfn(struct work_struct *work) } if (!list_empty(&wb->work_list)) - mod_delayed_work(bdi_wq, &wb->dwork, 0); + wb_wakeup(wb); else if (wb_has_dirty_io(wb) && dirty_writeback_interval) wb_wakeup_delayed(wb); -- 2.13.6
Re: [PATCH] bdi: Fix oops in wb_workfn()
On Thu, May 03, 2018 at 06:26:26PM +0200, Jan Kara wrote: > Syzbot has reported that it can hit a NULL pointer dereference in > wb_workfn() due to wb->bdi->dev being NULL. This indicates that > wb_workfn() was called for an already unregistered bdi which should not > happen as wb_shutdown() called from bdi_unregister() should make sure > all pending writeback works are completed before bdi is unregistered. > Except that wb_workfn() itself can requeue the work with: > > mod_delayed_work(bdi_wq, &wb->dwork, 0); > > and if this happens while wb_shutdown() is waiting in: > > flush_delayed_work(&wb->dwork); > > the dwork can get executed after wb_shutdown() has finished and > bdi_unregister() has cleared wb->bdi->dev. > > Make wb_workfn() use wakeup_wb() for requeueing the work which takes all > the necessary precautions against racing with bdi unregistration. > > CC: Tetsuo Handa > CC: Tejun Heo > Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977 > Reported-by: syzbot > Signed-off-by: Jan Kara > --- > fs/fs-writeback.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c > index 47d7c151fcba..471d863958bc 100644 > --- a/fs/fs-writeback.c > +++ b/fs/fs-writeback.c > @@ -1961,7 +1961,7 @@ void wb_workfn(struct work_struct *work) > } > > if (!list_empty(&wb->work_list)) > - mod_delayed_work(bdi_wq, &wb->dwork, 0); > + wb_wakeup(wb); > else if (wb_has_dirty_io(wb) && dirty_writeback_interval) > wb_wakeup_delayed(wb); Yup, looks fine - I can't see any more of these open coded wakeup, either, so we should be good here. Reviewed-by: Dave Chinner As an aside, why is half the wb infrastructure in fs/fs-writeback.c and the other half in mm/backing-dev.c? it seems pretty random as to what is where e.g. wb_wakeup() and wb_wakeup_delayed() are almost identical, but are in completely different files... Cheers, Dave. -- Dave Chinner da...@fromorbit.com
Re: [PATCH] bdi: Fix oops in wb_workfn()
On 5/3/18 3:55 PM, Dave Chinner wrote: > On Thu, May 03, 2018 at 06:26:26PM +0200, Jan Kara wrote: >> Syzbot has reported that it can hit a NULL pointer dereference in >> wb_workfn() due to wb->bdi->dev being NULL. This indicates that >> wb_workfn() was called for an already unregistered bdi which should not >> happen as wb_shutdown() called from bdi_unregister() should make sure >> all pending writeback works are completed before bdi is unregistered. >> Except that wb_workfn() itself can requeue the work with: >> >> mod_delayed_work(bdi_wq, &wb->dwork, 0); >> >> and if this happens while wb_shutdown() is waiting in: >> >> flush_delayed_work(&wb->dwork); >> >> the dwork can get executed after wb_shutdown() has finished and >> bdi_unregister() has cleared wb->bdi->dev. >> >> Make wb_workfn() use wakeup_wb() for requeueing the work which takes all >> the necessary precautions against racing with bdi unregistration. >> >> CC: Tetsuo Handa >> CC: Tejun Heo >> Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977 >> Reported-by: syzbot >> Signed-off-by: Jan Kara >> --- >> fs/fs-writeback.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c >> index 47d7c151fcba..471d863958bc 100644 >> --- a/fs/fs-writeback.c >> +++ b/fs/fs-writeback.c >> @@ -1961,7 +1961,7 @@ void wb_workfn(struct work_struct *work) >> } >> >> if (!list_empty(&wb->work_list)) >> -mod_delayed_work(bdi_wq, &wb->dwork, 0); >> +wb_wakeup(wb); >> else if (wb_has_dirty_io(wb) && dirty_writeback_interval) >> wb_wakeup_delayed(wb); > > Yup, looks fine - I can't see any more of these open coded wakeup, > either, so we should be good here. > > Reviewed-by: Dave Chinner > > As an aside, why is half the wb infrastructure in fs/fs-writeback.c > and the other half in mm/backing-dev.c? it seems pretty random as to > what is where e.g. wb_wakeup() and wb_wakeup_delayed() are almost > identical, but are in completely different files... That's always bothered me too, it's due for a cleanup and bringing it all into one location. -- Jens Axboe
Re: [PATCH] bdi: Fix oops in wb_workfn()
Jan Kara wrote: > Make wb_workfn() use wakeup_wb() for requeueing the work which takes all > the necessary precautions against racing with bdi unregistration. Yes, this patch will solve NULL pointer dereference bug. But is it OK to leave list_empty(&wb->work_list) == false situation? Who takes over the role of making list_empty(&wb->work_list) == true? Just a confirmation, for Fabiano Rosas is facing a problem that "write call hangs in kernel space after virtio hot-remove" and is thinking that we might need to go the opposite direction ( http://lkml.kernel.org/r/f0787b79-1e50-5f55-a400-44f715451...@linux.ibm.com ).
Re: [PATCH] bdi: Fix oops in wb_workfn()
On Fri 04-05-18 07:35:34, Tetsuo Handa wrote:
> Jan Kara wrote:
> > Make wb_workfn() use wakeup_wb() for requeueing the work which takes all
> > the necessary precautions against racing with bdi unregistration.
>
> Yes, this patch will solve NULL pointer dereference bug. But is it OK to
> leave list_empty(&wb->work_list) == false situation? Who takes over the
> role of making list_empty(&wb->work_list) == true?
That's a good question. The reason is the last running instance of
wb_workfn() cannot leave with the work_list non-empty. Once WB_registered
is cleared we cannot add new entries to work_list. Then we'll queue and
flush last wb_workfn() to clean up the list. The problem with NULL ptr
deref has been triggered not by this last running wb_workfn() but by one
running independently in parallel to wb_shutdown(). So something like:
CPU0CPU1CPU2
wb_workfn()
do {
...
} while (!list_empty(&wb->work_list));
wb_queue_work()
if (test_bit(WB_registered, &wb->state)) {
list_add_tail(&work->list, &wb->work_list);
mod_delayed_work(bdi_wq, &wb->dwork, 0);
}
wb_shutdown()
if
(!test_and_clear_bit(WB_registered, &wb->state)) {
...
mod_delayed_work(bdi_wq,
&wb->dwork, 0);
flush_delayed_work(&wb->dwork);
if (!list_empty(&wb->work_list))
mod_delayed_work(bdi_wq, &wb->dwork, 0); -> queues buggy work
> Just a confirmation, for Fabiano Rosas is facing a problem that "write call
> hangs in kernel space after virtio hot-remove" and is thinking that we might
> need to go the opposite direction
> ( http://lkml.kernel.org/r/f0787b79-1e50-5f55-a400-44f715451...@linux.ibm.com
> ).
Yes, I'm aware of that report and I think it should be solved
differently than what Fabiano suggests.
Honza
--
Jan Kara
SUSE Labs, CR
Re: [PATCH] bdi: Fix oops in wb_workfn()
On Fri 04-05-18 07:55:58, Dave Chinner wrote: > On Thu, May 03, 2018 at 06:26:26PM +0200, Jan Kara wrote: > > Syzbot has reported that it can hit a NULL pointer dereference in > > wb_workfn() due to wb->bdi->dev being NULL. This indicates that > > wb_workfn() was called for an already unregistered bdi which should not > > happen as wb_shutdown() called from bdi_unregister() should make sure > > all pending writeback works are completed before bdi is unregistered. > > Except that wb_workfn() itself can requeue the work with: > > > > mod_delayed_work(bdi_wq, &wb->dwork, 0); > > > > and if this happens while wb_shutdown() is waiting in: > > > > flush_delayed_work(&wb->dwork); > > > > the dwork can get executed after wb_shutdown() has finished and > > bdi_unregister() has cleared wb->bdi->dev. > > > > Make wb_workfn() use wakeup_wb() for requeueing the work which takes all > > the necessary precautions against racing with bdi unregistration. > > > > CC: Tetsuo Handa > > CC: Tejun Heo > > Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977 > > Reported-by: syzbot > > Signed-off-by: Jan Kara > > --- > > fs/fs-writeback.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c > > index 47d7c151fcba..471d863958bc 100644 > > --- a/fs/fs-writeback.c > > +++ b/fs/fs-writeback.c > > @@ -1961,7 +1961,7 @@ void wb_workfn(struct work_struct *work) > > } > > > > if (!list_empty(&wb->work_list)) > > - mod_delayed_work(bdi_wq, &wb->dwork, 0); > > + wb_wakeup(wb); > > else if (wb_has_dirty_io(wb) && dirty_writeback_interval) > > wb_wakeup_delayed(wb); > > Yup, looks fine - I can't see any more of these open coded wakeup, > either, so we should be good here. > > Reviewed-by: Dave Chinner Thanks! > As an aside, why is half the wb infrastructure in fs/fs-writeback.c > and the other half in mm/backing-dev.c? it seems pretty random as to > what is where e.g. wb_wakeup() and wb_wakeup_delayed() are almost > identical, but are in completely different files... Yeah, it deserves a cleanup. Honza -- Jan Kara SUSE Labs, CR
Re: [PATCH] bdi: Fix oops in wb_workfn()
On Thu 03-05-18 18:26:26, Jan Kara wrote: > Syzbot has reported that it can hit a NULL pointer dereference in > wb_workfn() due to wb->bdi->dev being NULL. This indicates that > wb_workfn() was called for an already unregistered bdi which should not > happen as wb_shutdown() called from bdi_unregister() should make sure > all pending writeback works are completed before bdi is unregistered. > Except that wb_workfn() itself can requeue the work with: > > mod_delayed_work(bdi_wq, &wb->dwork, 0); > > and if this happens while wb_shutdown() is waiting in: > > flush_delayed_work(&wb->dwork); > > the dwork can get executed after wb_shutdown() has finished and > bdi_unregister() has cleared wb->bdi->dev. > > Make wb_workfn() use wakeup_wb() for requeueing the work which takes all > the necessary precautions against racing with bdi unregistration. > > CC: Tetsuo Handa > CC: Tejun Heo > Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977 > Reported-by: syzbot > Signed-off-by: Jan Kara > --- > fs/fs-writeback.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Jens, can you please pick up this patch? Probably for the next merge window (I don't see a reason to rush this at this point in release cycle). Thanks! Honza > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c > index 47d7c151fcba..471d863958bc 100644 > --- a/fs/fs-writeback.c > +++ b/fs/fs-writeback.c > @@ -1961,7 +1961,7 @@ void wb_workfn(struct work_struct *work) > } > > if (!list_empty(&wb->work_list)) > - mod_delayed_work(bdi_wq, &wb->dwork, 0); > + wb_wakeup(wb); > else if (wb_has_dirty_io(wb) && dirty_writeback_interval) > wb_wakeup_delayed(wb); > > -- > 2.13.6 > -- Jan Kara SUSE Labs, CR
Re: [PATCH] bdi: Fix oops in wb_workfn()
On 5/9/18 4:31 AM, Jan Kara wrote: > On Thu 03-05-18 18:26:26, Jan Kara wrote: >> Syzbot has reported that it can hit a NULL pointer dereference in >> wb_workfn() due to wb->bdi->dev being NULL. This indicates that >> wb_workfn() was called for an already unregistered bdi which should not >> happen as wb_shutdown() called from bdi_unregister() should make sure >> all pending writeback works are completed before bdi is unregistered. >> Except that wb_workfn() itself can requeue the work with: >> >> mod_delayed_work(bdi_wq, &wb->dwork, 0); >> >> and if this happens while wb_shutdown() is waiting in: >> >> flush_delayed_work(&wb->dwork); >> >> the dwork can get executed after wb_shutdown() has finished and >> bdi_unregister() has cleared wb->bdi->dev. >> >> Make wb_workfn() use wakeup_wb() for requeueing the work which takes all >> the necessary precautions against racing with bdi unregistration. >> >> CC: Tetsuo Handa >> CC: Tejun Heo >> Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977 >> Reported-by: syzbot >> Signed-off-by: Jan Kara >> --- >> fs/fs-writeback.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) > > Jens, can you please pick up this patch? Probably for the next merge window > (I don't see a reason to rush this at this point in release cycle). Thanks! Looks like I never replied that back, but I did pick it up, and it did in fact go out last week for this series. So we should be all good. I didn't see a need to postpone it, it's obviously correct and fixes a real issue. -- Jens Axboe
Re: [PATCH] bdi: Fix oops in wb_workfn()
Tetsuo Handa wrote:
> Jan Kara wrote:
> > Make wb_workfn() use wakeup_wb() for requeueing the work which takes all
> > the necessary precautions against racing with bdi unregistration.
>
> Yes, this patch will solve NULL pointer dereference bug. But is it OK to leave
> list_empty(&wb->work_list) == false situation? Who takes over the role of
> making
> list_empty(&wb->work_list) == true?
syzbot is again reporting the same NULL pointer dereference.
general protection fault in wb_workfn (2)
https://syzkaller.appspot.com/bug?id=e0818ccb7e46190b3f1038b0c794299208ed4206
Didn't we overlook something obvious in commit b8b784958eccbf8f ("bdi: Fix oops
in wb_workfn()") ?
At first, I thought that that commit will solve NULL pointer dereference bug.
But what does
if (!list_empty(&wb->work_list))
- mod_delayed_work(bdi_wq, &wb->dwork, 0);
+ wb_wakeup(wb);
else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
wb_wakeup_delayed(wb);
mean?
static void wb_wakeup(struct bdi_writeback *wb)
{
spin_lock_bh(&wb->work_lock);
if (test_bit(WB_registered, &wb->state))
mod_delayed_work(bdi_wq, &wb->dwork, 0);
spin_unlock_bh(&wb->work_lock);
}
It means nothing but "we don't call mod_delayed_work() if WB_registered bit was
already cleared".
But if WB_registered bit is not yet cleared when we hit wb_wakeup_delayed()
path?
void wb_wakeup_delayed(struct bdi_writeback *wb)
{
unsigned long timeout;
timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
spin_lock_bh(&wb->work_lock);
if (test_bit(WB_registered, &wb->state))
queue_delayed_work(bdi_wq, &wb->dwork, timeout);
spin_unlock_bh(&wb->work_lock);
}
add_timer() is called because (presumably) timeout > 0. And after that timeout
expires, __queue_work() is called even if WB_registered bit is already cleared
before that timeout expires, isn't it?
void delayed_work_timer_fn(struct timer_list *t)
{
struct delayed_work *dwork = from_timer(dwork, t, timer);
/* should have been called from irqsafe timer with irq already off */
__queue_work(dwork->cpu, dwork->wq, &dwork->work);
}
Then, wb_workfn() is after all scheduled even if we check for WB_registered bit,
isn't it?
Then, don't we need to check that
mod_delayed_work(bdi_wq, &wb->dwork, 0);
flush_delayed_work(&wb->dwork);
is really waiting for completion? At least, shouldn't we try below debug output
(not only for debugging this report but also generally desirable)?
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 7441bd9..ccec8cd 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -376,8 +376,10 @@ static void wb_shutdown(struct bdi_writeback *wb)
* tells wb_workfn() that @wb is dying and its work_list needs to
* be drained no matter what.
*/
- mod_delayed_work(bdi_wq, &wb->dwork, 0);
- flush_delayed_work(&wb->dwork);
+ if (!mod_delayed_work(bdi_wq, &wb->dwork, 0))
+ printk(KERN_WARNING "wb_shutdown: mod_delayed_work() failed\n");
+ if (!flush_delayed_work(&wb->dwork))
+ printk(KERN_WARNING "wb_shutdown: flush_delayed_work()
failed\n");
WARN_ON(!list_empty(&wb->work_list));
/*
* Make sure bit gets cleared after shutdown is finished. Matches with
Re: [PATCH] bdi: Fix oops in wb_workfn()
On Sat 19-05-18 23:27:09, Tetsuo Handa wrote:
> Tetsuo Handa wrote:
> > Jan Kara wrote:
> > > Make wb_workfn() use wakeup_wb() for requeueing the work which takes all
> > > the necessary precautions against racing with bdi unregistration.
> >
> > Yes, this patch will solve NULL pointer dereference bug. But is it OK to
> > leave
> > list_empty(&wb->work_list) == false situation? Who takes over the role of
> > making
> > list_empty(&wb->work_list) == true?
>
> syzbot is again reporting the same NULL pointer dereference.
>
> general protection fault in wb_workfn (2)
>
> https://syzkaller.appspot.com/bug?id=e0818ccb7e46190b3f1038b0c794299208ed4206
Gaah... So we are still missing something.
> Didn't we overlook something obvious in commit b8b784958eccbf8f ("bdi:
> Fix oops in wb_workfn()") ?
>
> At first, I thought that that commit will solve NULL pointer dereference bug.
> But what does
>
> if (!list_empty(&wb->work_list))
> - mod_delayed_work(bdi_wq, &wb->dwork, 0);
> + wb_wakeup(wb);
> else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
> wb_wakeup_delayed(wb);
>
> mean?
>
> static void wb_wakeup(struct bdi_writeback *wb)
> {
> spin_lock_bh(&wb->work_lock);
> if (test_bit(WB_registered, &wb->state))
> mod_delayed_work(bdi_wq, &wb->dwork, 0);
> spin_unlock_bh(&wb->work_lock);
> }
>
> It means nothing but "we don't call mod_delayed_work() if WB_registered
> bit was already cleared".
Exactly.
> But if WB_registered bit is not yet cleared when we hit
> wb_wakeup_delayed() path?
>
> void wb_wakeup_delayed(struct bdi_writeback *wb)
> {
> unsigned long timeout;
>
> timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
> spin_lock_bh(&wb->work_lock);
> if (test_bit(WB_registered, &wb->state))
> queue_delayed_work(bdi_wq, &wb->dwork, timeout);
> spin_unlock_bh(&wb->work_lock);
> }
>
> add_timer() is called because (presumably) timeout > 0. And after that
> timeout expires, __queue_work() is called even if WB_registered bit is
> already cleared before that timeout expires, isn't it?
Yes.
> void delayed_work_timer_fn(struct timer_list *t)
> {
> struct delayed_work *dwork = from_timer(dwork, t, timer);
>
> /* should have been called from irqsafe timer with irq already off */
> __queue_work(dwork->cpu, dwork->wq, &dwork->work);
> }
>
> Then, wb_workfn() is after all scheduled even if we check for
> WB_registered bit, isn't it?
It can be queued after WB_registered bit is cleared but it cannot be queued
after mod_delayed_work(bdi_wq, &wb->dwork, 0) has finished. That function
deletes the pending timer (the timer cannot be armed again because
WB_registered is cleared) and queues what should be the last round of
wb_workfn().
> Then, don't we need to check that
>
> mod_delayed_work(bdi_wq, &wb->dwork, 0);
> flush_delayed_work(&wb->dwork);
>
> is really waiting for completion? At least, shouldn't we try below debug
> output (not only for debugging this report but also generally desirable)?
>
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index 7441bd9..ccec8cd 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -376,8 +376,10 @@ static void wb_shutdown(struct bdi_writeback *wb)
>* tells wb_workfn() that @wb is dying and its work_list needs to
>* be drained no matter what.
>*/
> - mod_delayed_work(bdi_wq, &wb->dwork, 0);
> - flush_delayed_work(&wb->dwork);
> + if (!mod_delayed_work(bdi_wq, &wb->dwork, 0))
> + printk(KERN_WARNING "wb_shutdown: mod_delayed_work() failed\n");
false return from mod_delayed_work() just means that there was no timer
armed. That is a valid situation if there are no dirty data.
> + if (!flush_delayed_work(&wb->dwork))
> + printk(KERN_WARNING "wb_shutdown: flush_delayed_work()
> failed\n");
And this is valid as well (although unlikely) if the work managed to
complete on another CPU before flush_delayed_work() was called.
So I don't think your warnings will help us much. But yes, we need to debug
this somehow. For now I have no idea what could be still going wrong.
Honza
--
Jan Kara
SUSE Labs, CR
Re: [PATCH] bdi: Fix oops in wb_workfn()
Jan Kara wrote:
> > void delayed_work_timer_fn(struct timer_list *t)
> > {
> > struct delayed_work *dwork = from_timer(dwork, t, timer);
> >
> > /* should have been called from irqsafe timer with irq already off */
> > __queue_work(dwork->cpu, dwork->wq, &dwork->work);
> > }
> >
> > Then, wb_workfn() is after all scheduled even if we check for
> > WB_registered bit, isn't it?
>
> It can be queued after WB_registered bit is cleared but it cannot be queued
> after mod_delayed_work(bdi_wq, &wb->dwork, 0) has finished. That function
> deletes the pending timer (the timer cannot be armed again because
> WB_registered is cleared) and queues what should be the last round of
> wb_workfn().
mod_delayed_work() deletes the pending timer but does not wait for already
invoked timer handler to complete because it is using del_timer() rather than
del_timer_sync(). Then, what happens if __queue_work() is almost concurrently
executed from two CPUs, one from mod_delayed_work(bdi_wq, &wb->dwork, 0) from
wb_shutdown() path (which is called without spin_lock_bh(&wb->work_lock)) and
the other from delayed_work_timer_fn() path (which is called without checking
WB_registered bit under spin_lock_bh(&wb->work_lock)) ?
wb_wakeup_delayed() {
spin_lock_bh(&wb->work_lock);
if (test_bit(WB_registered, &wb->state)) // succeeds
queue_delayed_work(bdi_wq, &wb->d_work, timeout) {
queue_delayed_work_on(WORK_CPU_UNBOUND, bdi_wq, &wb->d_work, timeout) {
if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT,
work_data_bits(&wb->d_work.work))) { // succeeds
__queue_delayed_work(WORK_CPU_UNBOUND, bdi_wq, &wb->d_work, timeout)
{
add_timer(timer); // schedules for delayed_work_timer_fn()
}
}
}
}
spin_unlock_bh(&wb->work_lock);
}
delayed_work_timer_fn() {
// del_timer() already returns false at this point because this timer
// is already inside handler. But something took long here enough to
// wait for __queue_work() from wb_shutdown() path to finish?
__queue_work(WORK_CPU_UNBOUND, bdi_wq, &wb->d_work.work) {
insert_work(pwq, work, worklist, work_flags);
}
}
wb_shutdown() {
mod_delayed_work(bdi_wq, &wb->dwork, 0) {
mod_delayed_work_on(WORK_CPU_UNBOUND, bdi_wq, &wb->dwork, 0) {
ret = try_to_grab_pending(&wb->dwork.work, true, &flags) {
if (likely(del_timer(&wb->dwork.timer))) // fails because already in
delayed_work_timer_fn()
return 1;
if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT,
work_data_bits(&wb->dwork.work))) // fails because already set by
queue_delayed_work()
return 0;
// Returns 1 or -ENOENT after doing something?
}
if (ret >= 0)
__queue_delayed_work(WORK_CPU_UNBOUND, bdi_wq, &wb->dwork, 0) {
__queue_work(WORK_CPU_UNBOUND, bdi_wq, &wb->dwork.work) {
insert_work(pwq, work, worklist, work_flags);
}
}
}
}
}
