diff mbox series

[7/7] loop: use WQ_MEM_RECLAIM flag

Message ID 20220129071500.3566-8-penguin-kernel@I-love.SAKURA.ne.jp (mailing list archive)
State New, archived
Headers show
Series [1/7] loop: revert "make autoclear operation asynchronous" | expand

Commit Message

Tetsuo Handa Jan. 29, 2022, 7:15 a.m. UTC 
Allocating kworker threads on demand has a risk of OOM deadlock.
Make sure that each loop device has at least one execution context.

Cc: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 drivers/block/loop.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index b45198f2d76b..a2f0397d29e5 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1003,11 +1003,20 @@  static int loop_configure(struct loop_device *lo, fmode_t mode,
 	    !file->f_op->write_iter)
 		lo->lo_flags |= LO_FLAGS_READ_ONLY;
 
+	/*
+	 * Allocate a WQ for this loop device. We can't use a global WQ because
+	 * an I/O request will hung when number of active work hits concurrency
+	 * limit due to stacked loop devices. Also, specify WQ_MEM_RECLAIM in
+	 * order to guarantee that loop_process_work() can start processing an
+	 * I/O request even under memory pressure. As a result, this allocation
+	 * sounds a sort of resource wasting prepared for the worst condition.
+	 * We hope that people utilize ioctl(LOOP_CTL_GET_FREE) in order to
+	 * create only minimal number of loop devices.
+	 */
 	if (!lo->workqueue)
-		lo->workqueue = alloc_workqueue("loop%d",
-					WQ_UNBOUND | WQ_FREEZABLE,
-					0,
-					lo->lo_number);
+		lo->workqueue = alloc_workqueue("loop%d", WQ_MEM_RECLAIM |
+						WQ_UNBOUND | WQ_FREEZABLE,
+						0, lo->lo_number);
 	if (!lo->workqueue) {
 		error = -ENOMEM;
 		goto out_unlock;