[PATCH -next v2 2/2] md/raid5-cache: fix null-ptr-deref in r5l_reclaim_thread()

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

r5l_reclaim_thread() already check that 'conf->log' is not NULL in the
beginning, however, r5c_do_reclaim() and r5l_do_reclaim() will
dereference 'conf->log' again, which will cause null-ptr-deref if
'conf->log' is set to NULL from r5l_exit_log() concurrently.

Fix this problem by don't dereference 'conf->log' again in
r5c_do_reclaim() and r5c_do_reclaim().

Fixes: a39f7afde358 ("md/r5cache: write-out phase and reclaim support")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 drivers/md/raid5-cache.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 083288e36949..ba6fc146d265 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -1148,10 +1148,9 @@ static void r5l_run_no_space_stripes(struct r5l_log *log)
  * for write through mode, returns log->next_checkpoint
  * for write back, returns log_start of first sh in stripe_in_journal_list
  */
-static sector_t r5c_calculate_new_cp(struct r5conf *conf)
+static sector_t r5c_calculate_new_cp(struct r5l_log *log)
 {
 	struct stripe_head *sh;
-	struct r5l_log *log = conf->log;
 	sector_t new_cp;
 	unsigned long flags;
 
@@ -1159,12 +1158,12 @@ static sector_t r5c_calculate_new_cp(struct r5conf *conf)
 		return log->next_checkpoint;
 
 	spin_lock_irqsave(&log->stripe_in_journal_lock, flags);
-	if (list_empty(&conf->log->stripe_in_journal_list)) {
+	if (list_empty(&log->stripe_in_journal_list)) {
 		/* all stripes flushed */
 		spin_unlock_irqrestore(&log->stripe_in_journal_lock, flags);
 		return log->next_checkpoint;
 	}
-	sh = list_first_entry(&conf->log->stripe_in_journal_list,
+	sh = list_first_entry(&log->stripe_in_journal_list,
 			      struct stripe_head, r5c);
 	new_cp = sh->log_start;
 	spin_unlock_irqrestore(&log->stripe_in_journal_lock, flags);
@@ -1173,10 +1172,8 @@ static sector_t r5c_calculate_new_cp(struct r5conf *conf)
 
 static sector_t r5l_reclaimable_space(struct r5l_log *log)
 {
-	struct r5conf *conf = log->rdev->mddev->private;
-
 	return r5l_ring_distance(log, log->last_checkpoint,
-				 r5c_calculate_new_cp(conf));
+				 r5c_calculate_new_cp(log));
 }
 
 static void r5l_run_no_mem_stripe(struct r5l_log *log)
@@ -1419,9 +1416,9 @@ void r5c_flush_cache(struct r5conf *conf, int num)
 	}
 }
 
-static void r5c_do_reclaim(struct r5conf *conf)
+static void r5c_do_reclaim(struct r5l_log *log)
 {
-	struct r5l_log *log = conf->log;
+	struct r5conf *conf = log->rdev->mddev->private;
 	struct stripe_head *sh;
 	int count = 0;
 	unsigned long flags;
@@ -1496,7 +1493,6 @@ static void r5c_do_reclaim(struct r5conf *conf)
 
 static void r5l_do_reclaim(struct r5l_log *log)
 {
-	struct r5conf *conf = log->rdev->mddev->private;
 	sector_t reclaim_target = xchg(&log->reclaim_target, 0);
 	sector_t reclaimable;
 	sector_t next_checkpoint;
@@ -1525,7 +1521,7 @@ static void r5l_do_reclaim(struct r5l_log *log)
 				    log->io_list_lock);
 	}
 
-	next_checkpoint = r5c_calculate_new_cp(conf);
+	next_checkpoint = r5c_calculate_new_cp(log);
 	spin_unlock_irq(&log->io_list_lock);
 
 	if (reclaimable == 0 || !write_super)
@@ -1554,7 +1550,7 @@ static void r5l_reclaim_thread(struct md_thread *thread)
 
 	if (!log)
 		return;
-	r5c_do_reclaim(conf);
+	r5c_do_reclaim(log);
 	r5l_do_reclaim(log);
 }
 
-- 
2.39.2