The function test_bit doesn't provide any memory barrier. It may be possible that the read requests that follow test_bit(B_READING, &b->state) are reordered before the test, reading invalid data that existed before B_READING was cleared.
Fix this bug by changing test_bit to test_bit_acquire. Signed-off-by: Mikulas Patocka <[email protected]> Cc: [email protected] --- drivers/md/dm-bufio.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) Index: linux-2.6/drivers/md/dm-bufio.c =================================================================== --- linux-2.6.orig/drivers/md/dm-bufio.c +++ linux-2.6/drivers/md/dm-bufio.c @@ -795,7 +795,7 @@ static void __make_buffer_clean(struct d { BUG_ON(b->hold_count); - if (!b->state) /* fast case */ + if (!smp_load_acquire(&b->state)) /* fast case */ return; wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE); @@ -816,7 +816,7 @@ static struct dm_buffer *__get_unclaimed BUG_ON(test_bit(B_DIRTY, &b->state)); if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep && - unlikely(test_bit(B_READING, &b->state))) + unlikely(test_bit_acquire(B_READING, &b->state))) continue; if (!b->hold_count) { @@ -1058,7 +1058,7 @@ found_buffer: * If the user called both dm_bufio_prefetch and dm_bufio_get on * the same buffer, it would deadlock if we waited. */ - if (nf == NF_GET && unlikely(test_bit(B_READING, &b->state))) + if (nf == NF_GET && unlikely(test_bit_acquire(B_READING, &b->state))) return NULL; b->hold_count++; @@ -1218,7 +1218,7 @@ void dm_bufio_release(struct dm_buffer * * invalid buffer. */ if ((b->read_error || b->write_error) && - !test_bit(B_READING, &b->state) && + !test_bit_acquire(B_READING, &b->state) && !test_bit(B_WRITING, &b->state) && !test_bit(B_DIRTY, &b->state)) { __unlink_buffer(b); @@ -1479,7 +1479,7 @@ EXPORT_SYMBOL_GPL(dm_bufio_release_move) static void forget_buffer_locked(struct dm_buffer *b) { - if (likely(!b->hold_count) && likely(!b->state)) { + if (likely(!b->hold_count) && likely(!smp_load_acquire(&b->state))) { __unlink_buffer(b); __free_buffer_wake(b); } @@ -1639,7 +1639,7 @@ static bool __try_evict_buffer(struct dm { if (!(gfp & __GFP_FS) || (static_branch_unlikely(&no_sleep_enabled) && b->c->no_sleep)) { - if (test_bit(B_READING, &b->state) || + if (test_bit_acquire(B_READING, &b->state) || test_bit(B_WRITING, &b->state) || test_bit(B_DIRTY, &b->state)) return false; -- dm-devel mailing list [email protected] https://listman.redhat.com/mailman/listinfo/dm-devel
