On Tue, 28 Feb 2023, yangerkun wrote:
>
>
> 在 2023/2/28 2:06, Mike Snitzer 写道:
> > On Mon, Feb 27 2023 at 1:03P -0500,
> > Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> >
> >> On Mon, Feb 27 2023 at 12:55P -0500,
> >> Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> >>
> >>> On Sun, Feb 26 2023 at 8:31P -0500,
> >>> yangerkun <yangerkun@xxxxxxxxxxxxxxx> wrote:
> >>>
> >>>>
> >>>>
> >>>> 在 2023/2/26 10:01, Bart Van Assche 写道:
> >>>>> On 2/22/23 19:19, yangerkun wrote:
> >>>>>> @@ -1924,6 +1926,10 @@ static int dmcrypt_write(void *data)
> >>>>>> BUG_ON(rb_parent(write_tree.rb_node));
> >>>>>> + if (time_is_before_jiffies(start_time + HZ)) {
> >>>>>> + schedule();
> >>>>>> + start_time = jiffies;
> >>>>>> + }
> >>>>>
> >>>>> Why schedule() instead of cond_resched()?
> >>>>
> >>>> cond_resched may not really schedule, which may trigger the problem too,
> but
> >>>> it seems after 1 second, it may never happend?
> >>>
> >>> I had the same question as Bart when reviewing your homegrown
> >>> conditional schedule(). Hopefully you can reproduce this issue? If
> >>> so, please see if simply using cond_resched() fixes the issue.
> >>
> >> This seems like a more appropriate patch:
> >>
> >> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> >> index 87c5706131f2..faba1be572f9 100644
> >> --- a/drivers/md/dm-crypt.c
> >> +++ b/drivers/md/dm-crypt.c
> >> @@ -1937,6 +1937,7 @@ static int dmcrypt_write(void *data)
> >> io = crypt_io_from_node(rb_first(&write_tree));
> >> rb_erase(&io->rb_node, &write_tree);
> >> kcryptd_io_write(io);
> >> + cond_resched();
> >> } while (!RB_EMPTY_ROOT(&write_tree));
> >> blk_finish_plug(&plug);
> >> }
> >
> >
> > or:
> >
> > diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> > index 87c5706131f2..3ba2fd3e4358 100644
> > --- a/drivers/md/dm-crypt.c
> > +++ b/drivers/md/dm-crypt.c
> > @@ -1934,6 +1934,7 @@ static int dmcrypt_write(void *data)
> > */
> > blk_start_plug(&plug);
> > do {
> > + cond_resched();
> > io = crypt_io_from_node(rb_first(&write_tree));
> > rb_erase(&io->rb_node, &write_tree);
> > kcryptd_io_write(io);
>
> Hi,
>
> Thanks a lot for your review!
>
> It's ok to fix the softlockup, but for async write encrypt,
> kcryptd_crypt_write_io_submit will add bio to write_tree, and once we
> call cond_resched before every kcryptd_io_write, the write performance
> may be poor while we meet a high cpu usage scene.
Hi
To fix this problem, find the PID of the process "dmcrypt_write" and
change its priority to -20, for example "renice -n -20 -p 34748".
This is the proper way how to fix it; locking up the process for one
second is not.
We used to have high-priority workqueues by default, but it caused audio
playback skipping, so we had to revert it - see
f612b2132db529feac4f965f28a1b9258ea7c22b.
Perhaps we should add an option to have high-priority kernel threads?
Mikulas
> kcryptd_crypt_write_io_submit will wakeup write_thread once there is a
> empty write_tree, and dmcrypt_write will peel the old write_tree to
> submit bio, so there can not exist too many bio in write_tree. Then I
> choose yield cpu before the 'while' that submit bio...
>
> Thanks,
> Kun.
>
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