On Fri, Jan 17, 2025 at 08:44:07AM +0100, Christoph Hellwig wrote: > 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 we call memalloc_noio_save() here, setting PF_MEMALLOC_NOIO can be removed from loop_process_work(). Thanks, Ming
