linux-kernel - [PATCH] lightnvm: pblk: fix race on sysfs line state

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Message-Id: <1537256432-19807-1-git-send-email-javier@cnexlabs.com>
Date:   Tue, 18 Sep 2018 09:40:32 +0200
From:   "Javier González" <javier@...igon.com>
To:     mb@...htnvm.io
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Javier González <javier@...xlabs.com>
Subject: [PATCH] lightnvm: pblk: fix race on sysfs line state

pblk exposes a sysfs interface that represents its internal state. Part
of this state is the map bitmap for the current open line, which should
be protected by the line lock to avoid a race when freeing the line
metadata. Currently, it is not.

This patch makes sure that the line state is consistent and NULL
bitmap pointers are not dereferenced.

Signed-off-by: Javier González <javier@...xlabs.com>
---
 drivers/lightnvm/pblk-core.c  | 5 +++--
 drivers/lightnvm/pblk-sysfs.c | 8 +++++++-
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/lightnvm/pblk-core.c b/drivers/lightnvm/pblk-core.c
index a23e965d32fc..fec0ad68dcd6 100644
--- a/drivers/lightnvm/pblk-core.c
+++ b/drivers/lightnvm/pblk-core.c
@@ -1662,13 +1662,14 @@ struct pblk_line *pblk_line_replace_data(struct pblk *pblk)
 	struct pblk_line *cur, *new = NULL;
 	unsigned int left_seblks;
 
-	cur = l_mg->data_line;
 	new = l_mg->data_next;
 	if (!new)
 		goto out;
+
+	spin_lock(&l_mg->free_lock);
+	cur = l_mg->data_line;
 	l_mg->data_line = new;
 
-	spin_lock(&l_mg->free_lock);
 	pblk_line_setup_metadata(new, l_mg, &pblk->lm);
 	spin_unlock(&l_mg->free_lock);
 
diff --git a/drivers/lightnvm/pblk-sysfs.c b/drivers/lightnvm/pblk-sysfs.c
index cba83ac43e62..2d2818155aa8 100644
--- a/drivers/lightnvm/pblk-sysfs.c
+++ b/drivers/lightnvm/pblk-sysfs.c
@@ -263,8 +263,14 @@ static ssize_t pblk_sysfs_lines(struct pblk *pblk, char *page)
 		sec_in_line = l_mg->data_line->sec_in_line;
 		meta_weight = bitmap_weight(&l_mg->meta_bitmap,
 							PBLK_DATA_LINES);
-		map_weight = bitmap_weight(l_mg->data_line->map_bitmap,
+
+		spin_lock(&l_mg->data_line->lock);
+		if (l_mg->data_line->map_bitmap)
+			map_weight = bitmap_weight(l_mg->data_line->map_bitmap,
 							lm->sec_per_line);
+		else
+			map_weight = 0;
+		spin_unlock(&l_mg->data_line->lock);
 	}
 	spin_unlock(&l_mg->free_lock);
 
-- 
2.7.4