On Sat, Dec 09, 2017 at 03:32:18PM +0200, Nikolay Borisov wrote:
>
>
> On 9.12.2017 01:02, Liu Bo wrote:
> > We're not allowed to take any new bios to rbio->bio_list in
> > rbio_orig_end_io(), otherwise we may get merged with more bios and
> > rbio->bio_list is not empty.
> >
> > This should only happens in error-out cases, the normal path of
> > recover and full stripe write have already set RBIO_RMW_LOCKED_BIT to
> > disable merge before doing IO.
> >
> > Reported-by: Jérôme Carretero <cJ-ko@xxxxxxxxxxx>
> > Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> > ---
> > fs/btrfs/raid56.c | 13 ++++++++++++-
> > 1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
> > index 5aa9d22..127c782 100644
> > --- a/fs/btrfs/raid56.c
> > +++ b/fs/btrfs/raid56.c
> > @@ -859,12 +859,23 @@ static void free_raid_bio(struct btrfs_raid_bio *rbio)
> > */
> > static void rbio_orig_end_io(struct btrfs_raid_bio *rbio, blk_status_t err)
> > {
> > - struct bio *cur = bio_list_get(&rbio->bio_list);
> > + struct bio *cur;
> > struct bio *next;
> >
> > + /*
> > + * We're not allowed to take any new bios to rbio->bio_list
> > + * from now on, otherwise we may get merged with more bios and
> > + * rbio->bio_list is not empty.
> > + */
> > + spin_lock(&rbio->bio_list_lock);
> > + set_bit(RBIO_RMW_LOCKED_BIT, &rbio->flags);
> > + spin_unlock(&rbio->bio_list_lock);
>
> do we really need the spinlock, bit operations are atomic?
>
Thanks for the question.
Atomicity doesn't really matter here, set_bit() needs to be done in
the critical section so that merge_rbio() can do right things if
merge_rbio() comes after rbio_orig_end_io().
thanks,
-liubo
> > +
> > if (rbio->generic_bio_cnt)
> > btrfs_bio_counter_sub(rbio->fs_info, rbio->generic_bio_cnt);
> >
> > + cur = bio_list_get(&rbio->bio_list);
> > +
> > free_raid_bio(rbio);
> >
> > while (cur) {
> >
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