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

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Date:	Wed, 3 Apr 2013 14:43:48 +0530 (IST)
From:	P J P <ppandit@...hat.com>
To:	Jaegeuk Kim <jaegeuk.kim@...sung.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

+-- On Wed, 3 Apr 2013, Jaegeuk Kim wrote --+
| I'm confusing the question because f2fs doesn't use generic_writepages(), 
| since f2fs_write_data_pages() is linked to a_ops->writepages. In 
| do_writepages(), always f2fs_write_data_pages() is triggered instead of 
| generic_writepages(). Isn't it?

Before commit fa9150a84c, when `generic_writepages' returned 0, it did not 
abort `f2fs_write_data_pages', as the proposed patch does. I was wondering if 
that's intentional OR if the patch below does it right?

===
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 7bd22a2..7be750e 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -561,7 +561,7 @@ static int f2fs_write_data_pages(struct address_space 
*mapping,
 {
        struct inode *inode = mapping->host;
        struct f2fs_sb_info *sbi = F2FS_SB(inode->i_sb);
-       int ret;
+       int ret = 0;
        long excess_nrtw = 0, desired_nrtw;
 
        if (wbc->nr_to_write < MAX_DESIRED_PAGES_WP) {
@@ -572,7 +572,9 @@ static int f2fs_write_data_pages(struct address_space *mapping,
 
        if (!S_ISDIR(inode->i_mode))
                mutex_lock(&sbi->writepages);
-       ret = write_cache_pages(mapping, wbc, __f2fs_writepage, mapping);
+       /* deal with chardevs and other special file */
+       if (mapping->a_ops->writepage)
+               ret = write_cache_pages(mapping, wbc, __f2fs_writepage, mapping);
        if (!S_ISDIR(inode->i_mode))
                mutex_unlock(&sbi->writepages);
        f2fs_submit_bio(sbi, DATA, (wbc->sync_mode == WB_SYNC_ALL));
===

Thank you.
--
Prasad J Pandit / Red Hat Security Response Team
DB7A 84C5 D3F9 7CD1 B5EB  C939 D048 7860 3655 602B
--
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