linux-kernel - Re: [PATCH] To add NULL pointer check

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Date:	Wed, 03 Apr 2013 12:03:13 +0900
From:	Jaegeuk Kim <jaegeuk.kim@...sung.com>
To:	P J P <ppandit@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Petr Matousek <pmatouse@...hat.com>
Subject: Re: [PATCH] To add NULL pointer check

Hi,
Thank you for your contribution.

As I consider the null pointer check, generic_writepages() originally
does so.
Therefore, I think f2fs_write_data_pages() is better to handle this.
Please review the modified patch. 
Thanks,

---
From d3c811a51c7062fb1b66bec910ed346447c02032 Mon Sep 17 00:00:00 2001
From: P J P <ppandit@...hat.com>
Date: Wed, 3 Apr 2013 11:38:00 +0900
Subject: [PATCH] f2fs: add NULL pointer check
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net

Commit - fa9150a84c - replaces a call to generic_writepages() in
f2fs_write_data_pages() with write_cache_pages(), with a function
pointer
argument pointing to routine: __f2fs_writepage.

  ->
https://git.kernel.org/linus/fa9150a84ca333f68127097c4fa1eda4b3913a22

  This patch adds a NULL pointer check in f2fs_write_data_pages() to
avoid
  a possible NULL pointer dereference, in case if -
mapping->a_ops->writepage -
  is NULL.

Signed-off-by: P J P <ppandit@...hat.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@...sung.com>
---
 fs/f2fs/data.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 47a2d7c..cf9ff5f 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -559,6 +559,10 @@ static int f2fs_write_data_pages(struct
address_space *mapping,
 	int ret;
 	long excess_nrtw = 0, desired_nrtw;
 
+	/* deal with chardevs and other special file */
+	if (!mapping->a_ops->writepage)
+		return 0;
+
 	if (wbc->nr_to_write < MAX_DESIRED_PAGES_WP) {
 		desired_nrtw = MAX_DESIRED_PAGES_WP;
 		excess_nrtw = desired_nrtw - wbc->nr_to_write;
-- 
1.8.1.3.566.gaa39828



-- 
Jaegeuk Kim
Samsung

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