| Message ID | 20130409180617.GB8907@blackbox.djwong.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue 09-04-13 11:06:17, Darrick J. Wong wrote: > Walking a bio's page mappings has proved problematic, so create a new bio flag > to indicate that a bio's data needs to be snapshotted in order to guarantee > stable pages during writeback. Next, for the one user (ext3/jbd) of > snapshotting, hook all the places where writes can be initiated without > PG_writeback set, and set BIO_SNAP_STABLE there. We must also flag journal > "metadata" bios for stable writeout, since file data can be written through the > journal. Finally, the MS_SNAP_STABLE mount flag (only used by ext3) is now > superfluous, so get rid of it. > > v3: Improve the documentation in jbd for why we're doing this, and clean up > some code. > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> > > [darrick.wong@oracle.com: Fold in a couple of small cleanups from akpm] > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> You can add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > fs/buffer.c | 9 ++++++++- > fs/ext3/super.c | 1 - > fs/jbd/commit.c | 25 ++++++++++++++++++++++--- > include/linux/blk_types.h | 3 ++- > include/linux/buffer_head.h | 1 + > include/uapi/linux/fs.h | 1 - > mm/bounce.c | 21 +-------------------- > mm/page-writeback.c | 4 ---- > 8 files changed, 34 insertions(+), 31 deletions(-) > > diff --git a/fs/buffer.c b/fs/buffer.c > index b4dcb34..71578d6 100644 > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -2949,7 +2949,7 @@ static void guard_bh_eod(int rw, struct bio *bio, struct buffer_head *bh) > } > } > > -int submit_bh(int rw, struct buffer_head * bh) > +int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags) > { > struct bio *bio; > int ret = 0; > @@ -2984,6 +2984,7 @@ int submit_bh(int rw, struct buffer_head * bh) > > bio->bi_end_io = end_bio_bh_io_sync; > bio->bi_private = bh; > + bio->bi_flags |= bio_flags; > > /* Take care of bh's that straddle the end of the device */ > guard_bh_eod(rw, bio, bh); > @@ -2997,6 +2998,12 @@ int submit_bh(int rw, struct buffer_head * bh) > bio_put(bio); > return ret; > } > +EXPORT_SYMBOL_GPL(_submit_bh); > + > +int submit_bh(int rw, struct buffer_head *bh) > +{ > + return _submit_bh(rw, bh, 0); > +} > EXPORT_SYMBOL(submit_bh); > > /** > diff --git a/fs/ext3/super.c b/fs/ext3/super.c > index fb5120a..3dc48cc 100644 > --- a/fs/ext3/super.c > +++ b/fs/ext3/super.c > @@ -2067,7 +2067,6 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent) > test_opt(sb,DATA_FLAGS) == EXT3_MOUNT_JOURNAL_DATA ? "journal": > test_opt(sb,DATA_FLAGS) == EXT3_MOUNT_ORDERED_DATA ? "ordered": > "writeback"); > - sb->s_flags |= MS_SNAP_STABLE; > > return 0; > > diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c > index 86b39b1..11bb11f 100644 > --- a/fs/jbd/commit.c > +++ b/fs/jbd/commit.c > @@ -162,8 +162,17 @@ static void journal_do_submit_data(struct buffer_head **wbuf, int bufs, > > for (i = 0; i < bufs; i++) { > wbuf[i]->b_end_io = end_buffer_write_sync; > - /* We use-up our safety reference in submit_bh() */ > - submit_bh(write_op, wbuf[i]); > + /* > + * Here we write back pagecache data that may be mmaped. Since > + * we cannot afford to clean the page and set PageWriteback > + * here due to lock ordering (page lock ranks above transaction > + * start), the data can change while IO is in flight. Tell the > + * block layer it should bounce the bio pages if stable data > + * during write is required. > + * > + * We use up our safety reference in submit_bh(). > + */ > + _submit_bh(write_op, wbuf[i], 1 << BIO_SNAP_STABLE); > } > } > > @@ -667,7 +676,17 @@ start_journal_io: > clear_buffer_dirty(bh); > set_buffer_uptodate(bh); > bh->b_end_io = journal_end_buffer_io_sync; > - submit_bh(write_op, bh); > + /* > + * In data=journal mode, here we can end up > + * writing pagecache data that might be > + * mmapped. Since we can't afford to clean the > + * page and set PageWriteback (see the comment > + * near the other use of _submit_bh()), the > + * data can change while the write is in > + * flight. Tell the block layer to bounce the > + * bio pages if stable pages are required. > + */ > + _submit_bh(write_op, bh, 1 << BIO_SNAP_STABLE); > } > cond_resched(); > > diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h > index cdf1119..22990cf 100644 > --- a/include/linux/blk_types.h > +++ b/include/linux/blk_types.h > @@ -111,12 +111,13 @@ struct bio { > #define BIO_FS_INTEGRITY 9 /* fs owns integrity data, not block layer */ > #define BIO_QUIET 10 /* Make BIO Quiet */ > #define BIO_MAPPED_INTEGRITY 11/* integrity metadata has been remapped */ > +#define BIO_SNAP_STABLE 12 /* bio data must be snapshotted during write */ > > /* > * Flags starting here get preserved by bio_reset() - this includes > * BIO_POOL_IDX() > */ > -#define BIO_RESET_BITS 12 > +#define BIO_RESET_BITS 13 > > #define bio_flagged(bio, flag) ((bio)->bi_flags & (1 << (flag))) > > diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h > index 5afc4f9..4c16c4a 100644 > --- a/include/linux/buffer_head.h > +++ b/include/linux/buffer_head.h > @@ -181,6 +181,7 @@ void ll_rw_block(int, int, struct buffer_head * bh[]); > int sync_dirty_buffer(struct buffer_head *bh); > int __sync_dirty_buffer(struct buffer_head *bh, int rw); > void write_dirty_buffer(struct buffer_head *bh, int rw); > +int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags); > int submit_bh(int, struct buffer_head *); > void write_boundary_block(struct block_device *bdev, > sector_t bblock, unsigned blocksize); > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h > index c7fc1e6..a4ed56c 100644 > --- a/include/uapi/linux/fs.h > +++ b/include/uapi/linux/fs.h > @@ -88,7 +88,6 @@ struct inodes_stat_t { > #define MS_STRICTATIME (1<<24) /* Always perform atime updates */ > > /* These sb flags are internal to the kernel */ > -#define MS_SNAP_STABLE (1<<27) /* Snapshot pages during writeback, if needed */ > #define MS_NOSEC (1<<28) > #define MS_BORN (1<<29) > #define MS_ACTIVE (1<<30) > diff --git a/mm/bounce.c b/mm/bounce.c > index 5f89017..a5c2ec3 100644 > --- a/mm/bounce.c > +++ b/mm/bounce.c > @@ -181,32 +181,13 @@ static void bounce_end_io_read_isa(struct bio *bio, int err) > #ifdef CONFIG_NEED_BOUNCE_POOL > static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio) > { > - struct page *page; > - struct backing_dev_info *bdi; > - struct address_space *mapping; > - struct bio_vec *from; > - int i; > - > if (bio_data_dir(bio) != WRITE) > return 0; > > if (!bdi_cap_stable_pages_required(&q->backing_dev_info)) > return 0; > > - /* > - * Based on the first page that has a valid mapping, decide whether or > - * not we have to employ bounce buffering to guarantee stable pages. > - */ > - bio_for_each_segment(from, bio, i) { > - page = from->bv_page; > - mapping = page_mapping(page); > - if (!mapping) > - continue; > - bdi = mapping->backing_dev_info; > - return mapping->host->i_sb->s_flags & MS_SNAP_STABLE; > - } > - > - return 0; > + return test_bit(BIO_SNAP_STABLE, &bio->bi_flags); > } > #else > static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio) > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index efe6814..4514ad7 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -2311,10 +2311,6 @@ void wait_for_stable_page(struct page *page) > > if (!bdi_cap_stable_pages_required(bdi)) > return; > -#ifdef CONFIG_NEED_BOUNCE_POOL > - if (mapping->host->i_sb->s_flags & MS_SNAP_STABLE) > - return; > -#endif /* CONFIG_NEED_BOUNCE_POOL */ > > wait_on_page_writeback(page); > }
On Tue, 9 Apr 2013 11:06:17 -0700 "Darrick J. Wong" <darrick.wong@oracle.com> wrote: > + * Here we write back pagecache data that may be mmaped. Since > + * we cannot afford to clean the page and set PageWriteback > + * here due to lock ordering (page lock ranks above transaction > + * start), the data can change while IO is in flight. Tell the > + * block layer it should bounce the bio pages if stable data > + * during write is required. I think there are already ab/ba deadlocks between lock_page() and journal_start(). iirc one path was write(), I forget which was the other path. This was 10+ years ago and nobody else noticed and I didn't know how to fix it so I didn't tell anyone ;) It would be neat to be able to hook things like journal_start() into lockdep but I don't think that lockdep has easy provision for wiring oddball things into its mechanisms.
On Tue 09-04-13 14:04:32, Andrew Morton wrote: > On Tue, 9 Apr 2013 11:06:17 -0700 "Darrick J. Wong" <darrick.wong@oracle.com> wrote: > > > + * Here we write back pagecache data that may be mmaped. Since > > + * we cannot afford to clean the page and set PageWriteback > > + * here due to lock ordering (page lock ranks above transaction > > + * start), the data can change while IO is in flight. Tell the > > + * block layer it should bounce the bio pages if stable data > > + * during write is required. > > I think there are already ab/ba deadlocks between lock_page() and > journal_start(). iirc one path was write(), I forget which was the > other path. This was 10+ years ago and nobody else noticed and I > didn't know how to fix it so I didn't tell anyone ;) Hum, I don't think they are there anymore ;) > It would be neat to be able to hook things like journal_start() into > lockdep but I don't think that lockdep has easy provision for wiring > oddball things into its mechanisms. Actually if you look at fs/jbd/transaction.c:start_this_handle(), you will notice that it is wired into lockdep (the lock_map_acquire() call there). And it works since I've seen quite some reports from it ;) Honza
diff --git a/fs/buffer.c b/fs/buffer.c index b4dcb34..71578d6 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -2949,7 +2949,7 @@ static void guard_bh_eod(int rw, struct bio *bio, struct buffer_head *bh) } } -int submit_bh(int rw, struct buffer_head * bh) +int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags) { struct bio *bio; int ret = 0; @@ -2984,6 +2984,7 @@ int submit_bh(int rw, struct buffer_head * bh) bio->bi_end_io = end_bio_bh_io_sync; bio->bi_private = bh; + bio->bi_flags |= bio_flags; /* Take care of bh's that straddle the end of the device */ guard_bh_eod(rw, bio, bh); @@ -2997,6 +2998,12 @@ int submit_bh(int rw, struct buffer_head * bh) bio_put(bio); return ret; } +EXPORT_SYMBOL_GPL(_submit_bh); + +int submit_bh(int rw, struct buffer_head *bh) +{ + return _submit_bh(rw, bh, 0); +} EXPORT_SYMBOL(submit_bh); /** diff --git a/fs/ext3/super.c b/fs/ext3/super.c index fb5120a..3dc48cc 100644 --- a/fs/ext3/super.c +++ b/fs/ext3/super.c @@ -2067,7 +2067,6 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent) test_opt(sb,DATA_FLAGS) == EXT3_MOUNT_JOURNAL_DATA ? "journal": test_opt(sb,DATA_FLAGS) == EXT3_MOUNT_ORDERED_DATA ? "ordered": "writeback"); - sb->s_flags |= MS_SNAP_STABLE; return 0; diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c index 86b39b1..11bb11f 100644 --- a/fs/jbd/commit.c +++ b/fs/jbd/commit.c @@ -162,8 +162,17 @@ static void journal_do_submit_data(struct buffer_head **wbuf, int bufs, for (i = 0; i < bufs; i++) { wbuf[i]->b_end_io = end_buffer_write_sync; - /* We use-up our safety reference in submit_bh() */ - submit_bh(write_op, wbuf[i]); + /* + * Here we write back pagecache data that may be mmaped. Since + * we cannot afford to clean the page and set PageWriteback + * here due to lock ordering (page lock ranks above transaction + * start), the data can change while IO is in flight. Tell the + * block layer it should bounce the bio pages if stable data + * during write is required. + * + * We use up our safety reference in submit_bh(). + */ + _submit_bh(write_op, wbuf[i], 1 << BIO_SNAP_STABLE); } } @@ -667,7 +676,17 @@ start_journal_io: clear_buffer_dirty(bh); set_buffer_uptodate(bh); bh->b_end_io = journal_end_buffer_io_sync; - submit_bh(write_op, bh); + /* + * In data=journal mode, here we can end up + * writing pagecache data that might be + * mmapped. Since we can't afford to clean the + * page and set PageWriteback (see the comment + * near the other use of _submit_bh()), the + * data can change while the write is in + * flight. Tell the block layer to bounce the + * bio pages if stable pages are required. + */ + _submit_bh(write_op, bh, 1 << BIO_SNAP_STABLE); } cond_resched(); diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index cdf1119..22990cf 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -111,12 +111,13 @@ struct bio { #define BIO_FS_INTEGRITY 9 /* fs owns integrity data, not block layer */ #define BIO_QUIET 10 /* Make BIO Quiet */ #define BIO_MAPPED_INTEGRITY 11/* integrity metadata has been remapped */ +#define BIO_SNAP_STABLE 12 /* bio data must be snapshotted during write */ /* * Flags starting here get preserved by bio_reset() - this includes * BIO_POOL_IDX() */ -#define BIO_RESET_BITS 12 +#define BIO_RESET_BITS 13 #define bio_flagged(bio, flag) ((bio)->bi_flags & (1 << (flag))) diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h index 5afc4f9..4c16c4a 100644 --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -181,6 +181,7 @@ void ll_rw_block(int, int, struct buffer_head * bh[]); int sync_dirty_buffer(struct buffer_head *bh); int __sync_dirty_buffer(struct buffer_head *bh, int rw); void write_dirty_buffer(struct buffer_head *bh, int rw); +int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags); int submit_bh(int, struct buffer_head *); void write_boundary_block(struct block_device *bdev, sector_t bblock, unsigned blocksize); diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index c7fc1e6..a4ed56c 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -88,7 +88,6 @@ struct inodes_stat_t { #define MS_STRICTATIME (1<<24) /* Always perform atime updates */ /* These sb flags are internal to the kernel */ -#define MS_SNAP_STABLE (1<<27) /* Snapshot pages during writeback, if needed */ #define MS_NOSEC (1<<28) #define MS_BORN (1<<29) #define MS_ACTIVE (1<<30) diff --git a/mm/bounce.c b/mm/bounce.c index 5f89017..a5c2ec3 100644 --- a/mm/bounce.c +++ b/mm/bounce.c @@ -181,32 +181,13 @@ static void bounce_end_io_read_isa(struct bio *bio, int err) #ifdef CONFIG_NEED_BOUNCE_POOL static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio) { - struct page *page; - struct backing_dev_info *bdi; - struct address_space *mapping; - struct bio_vec *from; - int i; - if (bio_data_dir(bio) != WRITE) return 0; if (!bdi_cap_stable_pages_required(&q->backing_dev_info)) return 0; - /* - * Based on the first page that has a valid mapping, decide whether or - * not we have to employ bounce buffering to guarantee stable pages. - */ - bio_for_each_segment(from, bio, i) { - page = from->bv_page; - mapping = page_mapping(page); - if (!mapping) - continue; - bdi = mapping->backing_dev_info; - return mapping->host->i_sb->s_flags & MS_SNAP_STABLE; - } - - return 0; + return test_bit(BIO_SNAP_STABLE, &bio->bi_flags); } #else static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index efe6814..4514ad7 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -2311,10 +2311,6 @@ void wait_for_stable_page(struct page *page) if (!bdi_cap_stable_pages_required(bdi)) return; -#ifdef CONFIG_NEED_BOUNCE_POOL - if (mapping->host->i_sb->s_flags & MS_SNAP_STABLE) - return; -#endif /* CONFIG_NEED_BOUNCE_POOL */ wait_on_page_writeback(page); }