Re: [dm-devel] dm-crypt: fix softlockup in dmcrypt_write

[Mike Snitzer <snitzer@kernel.org>]

On Mon, Feb 27 2023 at  1:03P -0500,
Mike Snitzer <snitzer@kernel.org> wrote:

> On Mon, Feb 27 2023 at 12:55P -0500,
> Mike Snitzer <snitzer@kernel.org> wrote:
> 
> > On Sun, Feb 26 2023 at  8:31P -0500,
> > yangerkun <yangerkun@huaweicloud.com> 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);

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