linux-kernel - [PATCH 5.13 032/104] io_uring: dont block level reissue off completion path

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Message-Id: <20210802134345.073963914@linuxfoundation.org>
Date:   Mon,  2 Aug 2021 15:44:29 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Fabian Ebner <f.ebner@...xmox.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.13 032/104] io_uring: dont block level reissue off completion path

From: Jens Axboe <axboe@...nel.dk>

commit ef04688871f3386b6d40ade8f5c664290420f819 upstream.

Some setups, like SCSI, can throw spurious -EAGAIN off the softirq
completion path. Normally we expect this to happen inline as part
of submission, but apparently SCSI has a weird corner case where it
can happen as part of normal completions.

This should be solved by having the -EAGAIN bubble back up the stack
as part of submission, but previous attempts at this failed and we're
not just quite there yet. Instead we currently use REQ_F_REISSUE to
handle this case.

For now, catch it in io_rw_should_reissue() and prevent a reissue
from a bogus path.

Cc: stable@...r.kernel.org
Reported-by: Fabian Ebner <f.ebner@...xmox.com>
Tested-by: Fabian Ebner <f.ebner@...xmox.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/io_uring.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2457,6 +2457,12 @@ static bool io_rw_should_reissue(struct
 	 */
 	if (percpu_ref_is_dying(&ctx->refs))
 		return false;
+	/*
+	 * Play it safe and assume not safe to re-import and reissue if we're
+	 * not in the original thread group (or in task context).
+	 */
+	if (!same_thread_group(req->task, current) || !in_task())
+		return false;
 	return true;
 }
 #else