zram: take device and not only bvec offset into account

Commit af8b04c63708 ("zram: simplify bvec iteration in
__zram_make_request") changed the bio iteration in zram to rely on the
implicit capping to page boundaries in bio_for_each_segment.  But it
failed to care for the fact zram not only care about the page alignment
of the bio payload, but also the page alignment into the device.  For
buffered I/O and swap those are the same, but for direct I/O or kernel
internal I/O like XFS log buffer writes they can differ.

Fix this by open coding bio_for_each_segment and limiting the bvec len
so that it never crosses over a page alignment boundary in the device
in addition to the payload boundary already taken care of by
bio_iter_iovec.

Cc: stable@vger.kernel.org
Fixes: af8b04c63708 ("zram: simplify bvec iteration in __zram_make_request")
Reported-by: Dusty Mabe <dusty@dustymabe.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Link: https://lore.kernel.org/r/20230805055537.147835-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 5676e6d..06673c6 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1870,15 +1870,16 @@ static void zram_bio_discard(struct zram *zram, struct bio *bio)
 
 static void zram_bio_read(struct zram *zram, struct bio *bio)
 {
-       struct bvec_iter iter;
-       struct bio_vec bv;
-       unsigned long start_time;
+       unsigned long start_time = bio_start_io_acct(bio);
+       struct bvec_iter iter = bio->bi_iter;
 
-       start_time = bio_start_io_acct(bio);
-       bio_for_each_segment(bv, bio, iter) {
+       do {
                u32 index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
                u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
                                SECTOR_SHIFT;
+               struct bio_vec bv = bio_iter_iovec(bio, iter);
+
+               bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset);
 
                if (zram_bvec_read(zram, &bv, index, offset, bio) < 0) {
                        atomic64_inc(&zram->stats.failed_reads);
@@ -1890,22 +1891,26 @@ static void zram_bio_read(struct zram *zram, struct bio *bio)
                zram_slot_lock(zram, index);
                zram_accessed(zram, index);
                zram_slot_unlock(zram, index);
-       }
+
+               bio_advance_iter_single(bio, &iter, bv.bv_len);
+       } while (iter.bi_size);
+
        bio_end_io_acct(bio, start_time);
        bio_endio(bio);
 }
 
 static void zram_bio_write(struct zram *zram, struct bio *bio)
 {
-       struct bvec_iter iter;
-       struct bio_vec bv;
-       unsigned long start_time;
+       unsigned long start_time = bio_start_io_acct(bio);
+       struct bvec_iter iter = bio->bi_iter;
 
-       start_time = bio_start_io_acct(bio);
-       bio_for_each_segment(bv, bio, iter) {
+       do {
                u32 index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
                u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
                                SECTOR_SHIFT;
+               struct bio_vec bv = bio_iter_iovec(bio, iter);
+
+               bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset);
 
                if (zram_bvec_write(zram, &bv, index, offset, bio) < 0) {
                        atomic64_inc(&zram->stats.failed_writes);
@@ -1916,7 +1921,10 @@ static void zram_bio_write(struct zram *zram, struct bio *bio)
                zram_slot_lock(zram, index);
                zram_accessed(zram, index);
                zram_slot_unlock(zram, index);
-       }
+
+               bio_advance_iter_single(bio, &iter, bv.bv_len);
+       } while (iter.bi_size);
+
        bio_end_io_acct(bio, start_time);
        bio_endio(bio);
 }