linux-kernel - [PATCH 3.16 033/192] md: don't use flush

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Message-ID: <lsq.1507553064.531011733@decadent.org.uk>
Date:   Mon, 09 Oct 2017 13:44:24 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "NeilBrown" <neilb@...e.com>,
        "Shaohua Li" <shli@...com>, "Mikulas Patocka" <mpatocka@...hat.com>
Subject: [PATCH 3.16 033/192] md: don't use flush_signals in userspace
 processes

3.16.49-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@...hat.com>

commit f9c79bc05a2a91f4fba8bfd653579e066714b1ec upstream.

The function flush_signals clears all pending signals for the process. It
may be used by kernel threads when we need to prepare a kernel thread for
responding to signals. However using this function for an userspaces
processes is incorrect - clearing signals without the program expecting it
can cause misbehavior.

The raid1 and raid5 code uses flush_signals in its request routine because
it wants to prepare for an interruptible wait. This patch drops
flush_signals and uses sigprocmask instead to block all signals (including
SIGKILL) around the schedule() call. The signals are not lost, but the
schedule() call won't respond to them.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
Acked-by: NeilBrown <neilb@...e.com>
Signed-off-by: Shaohua Li <shli@...com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/md/raid1.c | 5 ++++-
 drivers/md/raid5.c | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1122,13 +1122,16 @@ static void make_request(struct mddev *m
 		 */
 		DEFINE_WAIT(w);
 		for (;;) {
-			flush_signals(current);
+			sigset_t full, old;
 			prepare_to_wait(&conf->wait_barrier,
 					&w, TASK_INTERRUPTIBLE);
 			if (bio_end_sector(bio) <= mddev->suspend_lo ||
 			    bio->bi_iter.bi_sector >= mddev->suspend_hi)
 				break;
+			sigfillset(&full);
+			sigprocmask(SIG_BLOCK, &full, &old);
 			schedule();
+			sigprocmask(SIG_SETMASK, &old, NULL);
 		}
 		finish_wait(&conf->wait_barrier, &w);
 	}
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4721,12 +4721,15 @@ static void make_request(struct mddev *m
 				 * userspace, we want an interruptible
 				 * wait.
 				 */
-				flush_signals(current);
 				prepare_to_wait(&conf->wait_for_overlap,
 						&w, TASK_INTERRUPTIBLE);
 				if (logical_sector >= mddev->suspend_lo &&
 				    logical_sector < mddev->suspend_hi) {
+					sigset_t full, old;
+					sigfillset(&full);
+					sigprocmask(SIG_BLOCK, &full, &old);
 					schedule();
+					sigprocmask(SIG_SETMASK, &old, NULL);
 					do_prepare = true;
 				}
 				goto retry;