File systems can and often do allocate memory in the read-write path.
If these allocations are done with __GFP_IO or __GFP_FS set they can
recurse into the file system or swap device on top of the loop device
and cause deadlocks. Prevent this by forcing a noio scope over the
calls into the file system.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
drivers/block/loop.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 1ec7417c7f00..71eccc5cfffb 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1905,6 +1905,15 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
int ret = 0;
struct mem_cgroup *old_memcg = NULL;
const bool use_aio = cmd->use_aio;
+ unsigned int memflags;
+
+ /*
+ * We're calling into file system which could do be doing memory
+ * allocations. Ensure the memory reclaim does not cause I/O,
+ * because that could end up in the user of this loop devices again and
+ * deadlock.
+ */
+ memflags = memalloc_noio_save();
if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY)) {
ret = -EIO;
@@ -1942,6 +1951,7 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
if (likely(!blk_should_fake_timeout(rq->q)))
blk_mq_complete_request(rq);
}
+ memalloc_noio_restore(memflags);
}
static void loop_process_work(struct loop_worker *worker,
--
2.45.2
