The emergency thaw process uses iterate_super() which holds the
sb->s_umount lock in read mode. The current thaw_super() code takes
the sb->s_umount lock in write mode, hence leading to an instant
deadlock.
Use the unlocked version of thaw_super() to do the thawing and replace
iterate_supers() with __iterate_supers() so that the unfreeze operation can
be performed with s_umount held as the locking rules for fsfreeze indicate.
As a bonus, by using thaw_super(), which does not nest, instead of thaw_bdev()
when can get rid of the ugly while loop.
Cc: Josef Bacik <jbacik@xxxxxxxxxxxx>
Cc: Eric Sandeen <sandeen@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dave Chinner <dchinner@xxxxxxxxxx>
Signed-off-by: Fernando Luis Vazquez Cao <fernando@xxxxxxxxxxxxx>
---
diff -urNp linux-3.6-rc5-orig/fs/buffer.c linux-3.6-rc5/fs/buffer.c
--- linux-3.6-rc5-orig/fs/buffer.c 2012-09-14 12:46:22.988871880 +0900
+++ linux-3.6-rc5/fs/buffer.c 2012-09-14 13:05:47.812919103 +0900
@@ -513,15 +513,27 @@ repeat:
static void do_thaw_one(struct super_block *sb, void *unused)
{
- char b[BDEVNAME_SIZE];
- while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
- printk(KERN_WARNING "Emergency Thaw on %s\n",
+ int res;
+
+ if (sb->s_bdev) {
+ char b[BDEVNAME_SIZE];
+ printk(KERN_WARNING "Emergency Thaw on %s.\n",
bdevname(sb->s_bdev, b));
+ }
+
+ /* We were called from __iterate_supers with superblock lock taken
+ * so we do not need to do it here. */
+ res = __thaw_super(sb);
+ if (!res)
+ deactivate_locked_super(sb);
+ else
+ up_write(&sb->s_umount);
+ return res;
}
static void do_thaw_all(struct work_struct *work)
{
- iterate_supers_read(do_thaw_one, NULL);
+ iterate_supers_write(do_thaw_one, NULL);
kfree(work);
printk(KERN_WARNING "Emergency Thaw complete\n");
}
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
