Commit e732fe95 authored Sep 16, 2019 by Omar Sandoval Committed by David Sterba Nov 18, 2019

btrfs: don't prematurely free work in reada_start_machine_worker()



Currently, reada_start_machine_worker() frees the reada_machine_work and
then calls __reada_start_machine() to do readahead. This is another
potential instance of the bug in "btrfs: don't prematurely free work in
run_ordered_work()".

There _might_ already be a deadlock here: reada_start_machine_worker()
can depend on itself through stacked filesystems (__read_start_machine()
-> reada_start_machine_dev() -> reada_tree_block_flagged() ->
read_extent_buffer_pages() -> submit_one_bio() ->
btree_submit_bio_hook() -> btrfs_map_bio() -> submit_stripe_bio() ->
submit_bio() onto a loop device can trigger readahead on the lower
filesystem).

Either way, let's fix it by freeing the work at the end.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 9be490f1

fs/btrfs/reada.c

+4 −6

Original line number	Diff line number	Diff line
		@@ -752,21 +752,19 @@ static int reada_start_machine_dev(struct btrfs_device *dev)
		static void reada_start_machine_worker(struct btrfs_work *work)
		{
		struct reada_machine_work *rmw;
		struct btrfs_fs_info *fs_info;
		int old_ioprio;

		rmw = container_of(work, struct reada_machine_work, work);
		fs_info = rmw->fs_info;

		kfree(rmw);

		old_ioprio = IOPRIO_PRIO_VALUE(task_nice_ioclass(current),
		task_nice_ioprio(current));
		set_task_ioprio(current, BTRFS_IOPRIO_READA);
		__reada_start_machine(fs_info);
		__reada_start_machine(rmw->fs_info);
		set_task_ioprio(current, old_ioprio);

		atomic_dec(&fs_info->reada_works_cnt);
		atomic_dec(&rmw->fs_info->reada_works_cnt);

		kfree(rmw);
		}

		static void __reada_start_machine(struct btrfs_fs_info *fs_info)

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