dm bufio: change __GFP_IO to __GFP_FS in shrinker callbacks

commit 9d28eb12447ee08bb5d1e8bb3195cf20e1ecd1c0 upstream.

The shrinker uses gfp flags to indicate what kind of operation can the
driver wait for. If __GFP_IO flag is present, the driver can wait for
block I/O operations, if __GFP_FS flag is present, the driver can wait on
operations involving the filesystem.

dm-bufio tested for __GFP_IO. However, dm-bufio can run on a loop block
device that makes calls into the filesystem. If __GFP_IO is present and
__GFP_FS isn't, dm-bufio could still block on filesystem operations if it
runs on a loop block device.

The change from __GFP_IO to __GFP_FS supposedly fixes one observed (though
unreproducible) deadlock involving dm-bufio and loop device.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
[bwh: Backported to 3.2:
 - There's only one shrinker callback
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index 8abd681..3bf7267 100644 (file)
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -1324,9 +1324,9 @@ static void drop_buffers(struct dm_bufio_client *c)
 
 /*
  * Test if the buffer is unused and too old, and commit it.
- * At if noio is set, we must not do any I/O because we hold
- * dm_bufio_clients_lock and we would risk deadlock if the I/O gets rerouted to
- * different bufio client.
+ * And if GFP_NOFS is used, we must not do any I/O because we hold
+ * dm_bufio_clients_lock and we would risk deadlock if the I/O gets
+ * rerouted to different bufio client.
  */
 static int __cleanup_old_buffer(struct dm_buffer *b, gfp_t gfp,
                                unsigned long max_jiffies)
@@ -1334,7 +1334,7 @@ static int __cleanup_old_buffer(struct dm_buffer *b, gfp_t gfp,
        if (jiffies - b->last_accessed < max_jiffies)
                return 1;
 
-       if (!(gfp & __GFP_IO)) {
+       if (!(gfp & __GFP_FS)) {
                if (test_bit(B_READING, &b->state) ||
                    test_bit(B_WRITING, &b->state) ||
                    test_bit(B_DIRTY, &b->state))
@@ -1373,7 +1373,7 @@ static int shrink(struct shrinker *shrinker, struct shrink_control *sc)
        unsigned long r;
        unsigned long nr_to_scan = sc->nr_to_scan;
 
-       if (sc->gfp_mask & __GFP_IO)
+       if (sc->gfp_mask & __GFP_FS)
                dm_bufio_lock(c);
        else if (!dm_bufio_trylock(c))
                return !nr_to_scan ? 0 : -1;