From 196d38bccfcfa32faed8c561868336fdfa0fe8e4 Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Sat, 23 Nov 2013 18:34:15 -0800 Subject: block: Generic bio chaining This adds a generic mechanism for chaining bio completions. This is going to be used for a bio_split() replacement, and it turns out to be very useful in a fair amount of driver code - a fair number of drivers were implementing this in their own roundabout ways, often painfully. Note that this means it's no longer to call bio_endio() more than once on the same bio! This can cause problems for drivers that save/restore bi_end_io. Arguably they shouldn't be saving/restoring bi_end_io at all - in all but the simplest cases they'd be better off just cloning the bio, and immutable biovecs is making bio cloning cheaper. But for now, we add a bio_endio_nodec() for these cases. Signed-off-by: Kent Overstreet Cc: Jens Axboe --- fs/bio.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 70 insertions(+), 6 deletions(-) (limited to 'fs/bio.c') diff --git a/fs/bio.c b/fs/bio.c index e6dfa06773ac..b0a16dbc71ef 100644 --- a/fs/bio.c +++ b/fs/bio.c @@ -273,6 +273,7 @@ void bio_init(struct bio *bio) { memset(bio, 0, sizeof(*bio)); bio->bi_flags = 1 << BIO_UPTODATE; + atomic_set(&bio->bi_remaining, 1); atomic_set(&bio->bi_cnt, 1); } EXPORT_SYMBOL(bio_init); @@ -295,9 +296,35 @@ void bio_reset(struct bio *bio) memset(bio, 0, BIO_RESET_BYTES); bio->bi_flags = flags|(1 << BIO_UPTODATE); + atomic_set(&bio->bi_remaining, 1); } EXPORT_SYMBOL(bio_reset); +static void bio_chain_endio(struct bio *bio, int error) +{ + bio_endio(bio->bi_private, error); + bio_put(bio); +} + +/** + * bio_chain - chain bio completions + * + * The caller won't have a bi_end_io called when @bio completes - instead, + * @parent's bi_end_io won't be called until both @parent and @bio have + * completed; the chained bio will also be freed when it completes. + * + * The caller must not set bi_private or bi_end_io in @bio. + */ +void bio_chain(struct bio *bio, struct bio *parent) +{ + BUG_ON(bio->bi_private || bio->bi_end_io); + + bio->bi_private = parent; + bio->bi_end_io = bio_chain_endio; + atomic_inc(&parent->bi_remaining); +} +EXPORT_SYMBOL(bio_chain); + static void bio_alloc_rescue(struct work_struct *work) { struct bio_set *bs = container_of(work, struct bio_set, rescue_work); @@ -1719,16 +1746,53 @@ EXPORT_SYMBOL(bio_flush_dcache_pages); **/ void bio_endio(struct bio *bio, int error) { - if (error) - clear_bit(BIO_UPTODATE, &bio->bi_flags); - else if (!test_bit(BIO_UPTODATE, &bio->bi_flags)) - error = -EIO; + while (bio) { + BUG_ON(atomic_read(&bio->bi_remaining) <= 0); + + if (error) + clear_bit(BIO_UPTODATE, &bio->bi_flags); + else if (!test_bit(BIO_UPTODATE, &bio->bi_flags)) + error = -EIO; + + if (!atomic_dec_and_test(&bio->bi_remaining)) + return; - if (bio->bi_end_io) - bio->bi_end_io(bio, error); + /* + * Need to have a real endio function for chained bios, + * otherwise various corner cases will break (like stacking + * block devices that save/restore bi_end_io) - however, we want + * to avoid unbounded recursion and blowing the stack. Tail call + * optimization would handle this, but compiling with frame + * pointers also disables gcc's sibling call optimization. + */ + if (bio->bi_end_io == bio_chain_endio) { + struct bio *parent = bio->bi_private; + bio_put(bio); + bio = parent; + } else { + if (bio->bi_end_io) + bio->bi_end_io(bio, error); + bio = NULL; + } + } } EXPORT_SYMBOL(bio_endio); +/** + * bio_endio_nodec - end I/O on a bio, without decrementing bi_remaining + * @bio: bio + * @error: error, if any + * + * For code that has saved and restored bi_end_io; thing hard before using this + * function, probably you should've cloned the entire bio. + **/ +void bio_endio_nodec(struct bio *bio, int error) +{ + atomic_inc(&bio->bi_remaining); + bio_endio(bio, error); +} +EXPORT_SYMBOL(bio_endio_nodec); + void bio_pair_release(struct bio_pair *bp) { if (atomic_dec_and_test(&bp->cnt)) { -- cgit v1.2.3-59-g8ed1b