linux-kernel - [PATCH 5.16 0169/1017] bcache: fixup multiple threads crash

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Message-Id: <20220405070359.242350780@linuxfoundation.org>
Date:   Tue,  5 Apr 2022 09:18:02 +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, Mingzhe Zou <mingzhe.zou@...ystack.cn>,
        Coly Li <colyli@...e.de>
Subject: [PATCH 5.16 0169/1017] bcache: fixup multiple threads crash

From: Mingzhe Zou <mingzhe.zou@...ystack.cn>

commit 887554ab96588de2917b6c8c73e552da082e5368 upstream.

When multiple threads to check btree nodes in parallel, the main
thread wait for all threads to stop or CACHE_SET_IO_DISABLE flag:

wait_event_interruptible(check_state->wait,
                         atomic_read(&check_state->started) == 0 ||
                         test_bit(CACHE_SET_IO_DISABLE, &c->flags));

However, the bch_btree_node_read and bch_btree_node_read_done
maybe call bch_cache_set_error, then the CACHE_SET_IO_DISABLE
will be set. If the flag already set, the main thread return
error. At the same time, maybe some threads still running and
read NULL pointer, the kernel will crash.

This patch change the event wait condition, the main thread must
wait for all threads to stop.

Fixes: 8e7102273f597 ("bcache: make bch_btree_check() to be multithreaded")
Signed-off-by: Mingzhe Zou <mingzhe.zou@...ystack.cn>
Cc: stable@...r.kernel.org # v5.7+
Signed-off-by: Coly Li <colyli@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/md/bcache/btree.c     |    6 ++++--
 drivers/md/bcache/writeback.c |    6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -2060,9 +2060,11 @@ int bch_btree_check(struct cache_set *c)
 		}
 	}
 
+	/*
+	 * Must wait for all threads to stop.
+	 */
 	wait_event_interruptible(check_state->wait,
-				 atomic_read(&check_state->started) == 0 ||
-				  test_bit(CACHE_SET_IO_DISABLE, &c->flags));
+				 atomic_read(&check_state->started) == 0);
 
 	for (i = 0; i < check_state->total_threads; i++) {
 		if (check_state->infos[i].result) {
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -998,9 +998,11 @@ void bch_sectors_dirty_init(struct bcach
 		}
 	}
 
+	/*
+	 * Must wait for all threads to stop.
+	 */
 	wait_event_interruptible(state->wait,
-		 atomic_read(&state->started) == 0 ||
-		 test_bit(CACHE_SET_IO_DISABLE, &c->flags));
+		 atomic_read(&state->started) == 0);
 
 out:
 	kfree(state);