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 <[email protected]> --- 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
