On Tue 30-07-19 13:24:54, Thomas Gleixner wrote: > Bit spinlocks are problematic if PREEMPT_RT is enabled, because they > disable preemption, which is undesired for latency reasons and breaks when > regular spinlocks are taken within the bit_spinlock locked region because > regular spinlocks are converted to 'sleeping spinlocks' on RT. So RT > replaces the bit spinlocks with regular spinlocks to avoid this problem. > > To avoid ifdeffery at the source level, wrap all BH_Uptodate_Lock bitlock > operations with inline functions, so the spinlock substitution can be done > at one place. > > Using regular spinlocks can also be enabled for lock debugging purposes so > the lock operations become visible to lockdep. > > Signed-off-by: Thomas Gleixner <[email protected]> > Cc: "Theodore Ts'o" <[email protected]> > Cc: Matthew Wilcox <[email protected]> > Cc: Alexander Viro <[email protected]> > Cc: [email protected]
Looks good to me. You can add: Reviewed-by: Jan Kara <[email protected]> BTW, it should be possible to get rid of BH_Uptodate_Lock altogether using bio chaining (which was non-existent when this bh code was written) to make sure IO completion function gets called only once all bios used to fill in / write out the page are done. It would be also more efficient. But I guess that's an interesting cleanup project for some other time... Honza > --- > fs/buffer.c | 20 ++++++-------------- > fs/ext4/page-io.c | 6 ++---- > fs/ntfs/aops.c | 10 +++------- > include/linux/buffer_head.h | 16 ++++++++++++++++ > 4 files changed, 27 insertions(+), 25 deletions(-) > > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -275,8 +275,7 @@ static void end_buffer_async_read(struct > * decide that the page is now completely done. > */ > first = page_buffers(page); > - local_irq_save(flags); > - bit_spin_lock(BH_Uptodate_Lock, &first->b_state); > + flags = bh_uptodate_lock_irqsave(first); > clear_buffer_async_read(bh); > unlock_buffer(bh); > tmp = bh; > @@ -289,8 +288,7 @@ static void end_buffer_async_read(struct > } > tmp = tmp->b_this_page; > } while (tmp != bh); > - bit_spin_unlock(BH_Uptodate_Lock, &first->b_state); > - local_irq_restore(flags); > + bh_uptodate_unlock_irqrestore(first, flags); > > /* > * If none of the buffers had errors and they are all > @@ -302,9 +300,7 @@ static void end_buffer_async_read(struct > return; > > still_busy: > - bit_spin_unlock(BH_Uptodate_Lock, &first->b_state); > - local_irq_restore(flags); > - return; > + bh_uptodate_unlock_irqrestore(first, flags); > } > > /* > @@ -331,8 +327,7 @@ void end_buffer_async_write(struct buffe > } > > first = page_buffers(page); > - local_irq_save(flags); > - bit_spin_lock(BH_Uptodate_Lock, &first->b_state); > + flags = bh_uptodate_lock_irqsave(first); > > clear_buffer_async_write(bh); > unlock_buffer(bh); > @@ -344,15 +339,12 @@ void end_buffer_async_write(struct buffe > } > tmp = tmp->b_this_page; > } > - bit_spin_unlock(BH_Uptodate_Lock, &first->b_state); > - local_irq_restore(flags); > + bh_uptodate_unlock_irqrestore(first, flags); > end_page_writeback(page); > return; > > still_busy: > - bit_spin_unlock(BH_Uptodate_Lock, &first->b_state); > - local_irq_restore(flags); > - return; > + bh_uptodate_unlock_irqrestore(first, flags); > } > EXPORT_SYMBOL(end_buffer_async_write); > > --- a/fs/ext4/page-io.c > +++ b/fs/ext4/page-io.c > @@ -90,8 +90,7 @@ static void ext4_finish_bio(struct bio * > * We check all buffers in the page under BH_Uptodate_Lock > * to avoid races with other end io clearing async_write flags > */ > - local_irq_save(flags); > - bit_spin_lock(BH_Uptodate_Lock, &head->b_state); > + flags = bh_uptodate_lock_irqsave(head); > do { > if (bh_offset(bh) < bio_start || > bh_offset(bh) + bh->b_size > bio_end) { > @@ -103,8 +102,7 @@ static void ext4_finish_bio(struct bio * > if (bio->bi_status) > buffer_io_error(bh); > } while ((bh = bh->b_this_page) != head); > - bit_spin_unlock(BH_Uptodate_Lock, &head->b_state); > - local_irq_restore(flags); > + bh_uptodate_unlock_irqrestore(head, flags); > if (!under_io) { > fscrypt_free_bounce_page(bounce_page); > end_page_writeback(page); > --- a/fs/ntfs/aops.c > +++ b/fs/ntfs/aops.c > @@ -92,8 +92,7 @@ static void ntfs_end_buffer_async_read(s > "0x%llx.", (unsigned long long)bh->b_blocknr); > } > first = page_buffers(page); > - local_irq_save(flags); > - bit_spin_lock(BH_Uptodate_Lock, &first->b_state); > + flags = bh_uptodate_lock_irqsave(first); > clear_buffer_async_read(bh); > unlock_buffer(bh); > tmp = bh; > @@ -108,8 +107,7 @@ static void ntfs_end_buffer_async_read(s > } > tmp = tmp->b_this_page; > } while (tmp != bh); > - bit_spin_unlock(BH_Uptodate_Lock, &first->b_state); > - local_irq_restore(flags); > + bh_uptodate_unlock_irqrestore(first, flags); > /* > * If none of the buffers had errors then we can set the page uptodate, > * but we first have to perform the post read mst fixups, if the > @@ -142,9 +140,7 @@ static void ntfs_end_buffer_async_read(s > unlock_page(page); > return; > still_busy: > - bit_spin_unlock(BH_Uptodate_Lock, &first->b_state); > - local_irq_restore(flags); > - return; > + bh_uptodate_unlock_irqrestore(first, flags); > } > > /** > --- a/include/linux/buffer_head.h > +++ b/include/linux/buffer_head.h > @@ -78,6 +78,22 @@ struct buffer_head { > atomic_t b_count; /* users using this buffer_head */ > }; > > +static inline unsigned long bh_uptodate_lock_irqsave(struct buffer_head *bh) > +{ > + unsigned long flags; > + > + local_irq_save(flags); > + bit_spin_lock(BH_Uptodate_Lock, &bh->b_state); > + return flags; > +} > + > +static inline void > +bh_uptodate_unlock_irqrestore(struct buffer_head *bh, unsigned long flags) > +{ > + bit_spin_unlock(BH_Uptodate_Lock, &bh->b_state); > + local_irq_restore(flags); > +} > + > /* > * macro tricks to expand the set_buffer_foo(), clear_buffer_foo() > * and buffer_foo() functions. > > > -- Jan Kara <[email protected]> SUSE Labs, CR
