dm bufio: fix some cases where the code sleeps with spinlock held

Commit b32d45824aa7 ("dm bufio: Add DM_BUFIO_CLIENT_NO_SLEEP flag")
added a "NO_SLEEP" mode, it replaces a mutex with a spinlock, and it
is only usable when the device is in read-only mode (because the write
path may be sleeping while holding the dm_bufio_client lock).

However, there are still two points where the code could sleep even in
read-only mode. One is in __get_unclaimed_buffer -> __make_buffer_clean.
The other is in __try_evict_buffer -> __make_buffer_clean. These functions
will call __make_buffer_clean which sleeps if the buffer is being read.

Fix these cases so that if c->no_sleep is set __make_buffer_clean
will not be called and the buffer will be skipped instead.

Fixes: b32d45824aa7 ("dm bufio: Add DM_BUFIO_CLIENT_NO_SLEEP flag")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index bef8c6e..7999152 100644 (file)
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -815,6 +815,10 @@ static struct dm_buffer *__get_unclaimed_buffer(struct dm_bufio_client *c)
                BUG_ON(test_bit(B_WRITING, &b->state));
                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)))
+                       continue;
+
                if (!b->hold_count) {
                        __make_buffer_clean(b);
                        __unlink_buffer(b);
@@ -823,6 +827,9 @@ static struct dm_buffer *__get_unclaimed_buffer(struct dm_bufio_client *c)
                cond_resched();
        }
 
+       if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
+               return NULL;
+
        list_for_each_entry_reverse(b, &c->lru[LIST_DIRTY], lru_list) {
                BUG_ON(test_bit(B_READING, &b->state));
 
@@ -1632,7 +1639,8 @@ static void drop_buffers(struct dm_bufio_client *c)
  */
 static bool __try_evict_buffer(struct dm_buffer *b, gfp_t gfp)
 {
-       if (!(gfp & __GFP_FS)) {
+       if (!(gfp & __GFP_FS) ||
+           (static_branch_unlikely(&no_sleep_enabled) && b->c->no_sleep)) {
                if (test_bit(B_READING, &b->state) ||
                    test_bit(B_WRITING, &b->state) ||
                    test_bit(B_DIRTY, &b->state))