On Fri, Jan 12 2018 at 2:09am -0500,
Ming Lei <ming.lei@xxxxxxxxxx> wrote:
> On Thu, Jan 11, 2018 at 03:14:15PM -0500, Mike Snitzer wrote:
> > blk_unregister_queue() must protect against any modifications of
> > q->queue_flags (not just those performed in blk-sysfs.c). Therefore
> > q->queue_lock needs to be used rather than q->sysfs_lock.
> >
> > Fixes: e9a823fb34a8b ("block: fix warning when I/O elevator is changed as request_queue is being removed")
> > Cc: stable@xxxxxxxxxxxxxxx # 4.14+
> > Reported-by: Bart Van Assche <Bart.VanAssche@xxxxxxx>
> > Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> > ---
> > block/blk-sysfs.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> > index 870484eaed1f..52f57539f1c7 100644
> > --- a/block/blk-sysfs.c
> > +++ b/block/blk-sysfs.c
> > @@ -929,9 +929,9 @@ void blk_unregister_queue(struct gendisk *disk)
> > if (WARN_ON(!q))
> > return;
> >
> > - mutex_lock(&q->sysfs_lock);
> > + spin_lock_irq(q->queue_lock);
> > queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q);
> > - mutex_unlock(&q->sysfs_lock);
> > + spin_unlock_irq(q->queue_lock);
> >
> > wbt_exit(q);
>
> Hi Mike,
>
> This change may not be correct, since at least e9a823fb34a8b depends
> on q->sysfs_lock to sync between testing the flag in __elevator_change()
> and clearing it here.
The header for commit e9a823fb34a8b says:
To fix this warning, we can check the QUEUE_FLAG_REGISTERED flag when
changing the elevator and use the request_queue's sysfs_lock to
serialize between clearing the flag and the elevator testing the flag.
The reality is sysfs_lock isn't needed to serialize between
blk_unregister_queue() clearing the flag and __elevator_change() testing
the flag.
The original commit e9a823fb34a8b is pretty conflated. "conflated" because
the resource being protected isn't the queue_flags (it is the 'queue'
kobj).
I'll respin v5 of this patchset to fix this up first, and then apply the
changes I _really_ need to land (DM queue initialization fix).
And then I'm going to slowly step away from block core and _not_ allow
myself to be tripped up, or baited, by historic block core issues for a
while... ;)
Thanks,
Mike
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