This is a note to let you know that I've just added the patch titled
io_uring: check if we need to reschedule during overflow flush
to the 6.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
io_uring-check-if-we-need-to-reschedule-during-overf.patch
and it can be found in the queue-6.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 7e11e5ef025c9aa5a0b8b08ce654920e6d605c6c
Author: Jens Axboe <axboe@xxxxxxxxx>
Date: Fri Sep 20 02:51:20 2024 -0600
io_uring: check if we need to reschedule during overflow flush
[ Upstream commit eac2ca2d682f94f46b1973bdf5e77d85d77b8e53 ]
In terms of normal application usage, this list will always be empty.
And if an application does overflow a bit, it'll have a few entries.
However, nothing obviously prevents syzbot from running a test case
that generates a ton of overflow entries, and then flushing them can
take quite a while.
Check for needing to reschedule while flushing, and drop our locks and
do so if necessary. There's no state to maintain here as overflows
always prune from head-of-list, hence it's fine to drop and reacquire
the locks at the end of the loop.
Link: https://lore.kernel.org/io-uring/66ed061d.050a0220.29194.0053.GAE@xxxxxxxxxx/
Reported-by: syzbot+5fca234bd7eb378ff78e@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 7a166120a45c3..7057d942fb2b0 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -627,6 +627,21 @@ static void __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool dying)
}
list_del(&ocqe->list);
kfree(ocqe);
+
+ /*
+ * For silly syzbot cases that deliberately overflow by huge
+ * amounts, check if we need to resched and drop and
+ * reacquire the locks if so. Nothing real would ever hit this.
+ * Ideally we'd have a non-posting unlock for this, but hard
+ * to care for a non-real case.
+ */
+ if (need_resched()) {
+ io_cq_unlock_post(ctx);
+ mutex_unlock(&ctx->uring_lock);
+ cond_resched();
+ mutex_lock(&ctx->uring_lock);
+ io_cq_lock(ctx);
+ }
}
if (list_empty(&ctx->cq_overflow_list)) {
