From: majianpeng <majianpeng@gmail.com>
Date: Mon, 14 Jan 2013 12:08:16 +0000 (+0800)
Subject: f2fs: add global mutex_lock to protect f2fs_stat_list
X-Git-Tag: v3.8-rc5~24^2~7
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=66af62ce7588736ae65edfdb1c0df597775c4d21;p=pandora-kernel.git

f2fs: add global mutex_lock to protect f2fs_stat_list

There is an race condition between umounting f2fs and reading f2fs/status, which
results in oops.

Fox example:
Thread A			Thread B
umount f2fs 			cat f2fs/status

f2fs_destroy_stats() {		stat_show() {
				 list_for_each_entry_safe(&f2fs_stat_list)
 list_del(&si->stat_list);
 mutex_lock(&si->stat_lock);
 si->sbi = NULL;
 mutex_unlock(&si->stat_lock);
 kfree(sbi->stat_info);
} 				 mutex_lock(&si->stat_lock) <- si is gone.
				 ...
				}

Solution with a global lock: f2fs_stat_mutex:
Thread A			Thread B
umount f2fs 			cat f2fs/status

f2fs_destroy_stats() {		stat_show() {
 mutex_lock(&f2fs_stat_mutex);
 list_del(&si->stat_list);
 mutex_unlock(&f2fs_stat_mutex);
 kfree(sbi->stat_info);		 mutex_lock(&f2fs_stat_mutex);
}				 list_for_each_entry_safe(&f2fs_stat_list)
				 ...
				 mutex_unlock(&f2fs_stat_mutex);
				}

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
[jaegeuk.kim@samsung.com: fix typos, description, and remove the existing lock]
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
---

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