linux-kernel - [PATCH] libcfs: Fix a sleep-in-atomic bug in cfs_wi

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Date:   Wed, 31 May 2017 15:48:15 +0800
From:   Jia-Ju Bai <baijiaju1990@....com>
To:     oleg.drokin@...el.com, andreas.dilger@...el.com,
        jsimmons@...radead.org, gregkh@...uxfoundation.org,
        bobijam.xu@...el.com, dmitry.eremin@...el.com
Cc:     lustre-devel@...ts.lustre.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, Jia-Ju Bai <baijiaju1990@....com>
Subject: [PATCH] libcfs: Fix a sleep-in-atomic bug in cfs_wi_deschedule

The driver may sleep under a spin lock, and the function call path is:
cfs_wi_deschedule (acquire the lock by spin_lock)
  LASSERT
    lbug_with_loc
      libcfs_debug_dumplog
        schedule and kthread_run --> may sleep

To fix it, all "LASSERT" is placed out of the spin_lock and spin_unlock.

Signed-off-by: Jia-Ju Bai <baijiaju1990@....com>
---
 drivers/staging/lustre/lnet/libcfs/workitem.c |   11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/lustre/lnet/libcfs/workitem.c b/drivers/staging/lustre/lnet/libcfs/workitem.c
index dbc2a9b..7e25eb9 100644
--- a/drivers/staging/lustre/lnet/libcfs/workitem.c
+++ b/drivers/staging/lustre/lnet/libcfs/workitem.c
@@ -140,6 +140,11 @@ struct cfs_wi_sched {
 
 	LASSERT(!in_interrupt()); /* because we use plain spinlock */
 	LASSERT(!sched->ws_stopping);
+	if (wi->wi_scheduled) {
+		LASSERT(!list_empty(&wi->wi_list));
+		LASSERT(sched->ws_nscheduled > 0);
+	}
+	LASSERT(list_empty(&wi->wi_list));
 
 	/*
 	 * return 0 if it's running already, otherwise return 1, which
@@ -151,17 +156,11 @@ struct cfs_wi_sched {
 	rc = !(wi->wi_running);
 
 	if (wi->wi_scheduled) { /* cancel pending schedules */
-		LASSERT(!list_empty(&wi->wi_list));
 		list_del_init(&wi->wi_list);
-
-		LASSERT(sched->ws_nscheduled > 0);
 		sched->ws_nscheduled--;
-
 		wi->wi_scheduled = 0;
 	}
 
-	LASSERT(list_empty(&wi->wi_list));
-
 	spin_unlock(&sched->ws_lock);
 	return rc;
 }
-- 
1.7.9.5