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authorMiao Xie <miaox@cn.fujitsu.com>2013-02-08 07:01:08 +0000
committerJosef Bacik <jbacik@fusionio.com>2013-02-20 12:59:47 -0500
commit2e60a51e62185cce48758e596ae7cb2da673b58f (patch)
treebdbbac16110a3eeda8732c3ffb38a440204e2831 /fs/btrfs/btrfs_inode.h
parent0934856d4697e63c14056375e26e3bd6e8ebd34b (diff)
downloadlinux-2e60a51e62185cce48758e596ae7cb2da673b58f.tar.bz2
Btrfs: serialize unlocked dio reads with truncate
Currently, we can do unlocked dio reads, but the following race is possible: dio_read_task truncate_task ->btrfs_setattr() ->btrfs_direct_IO ->__blockdev_direct_IO ->btrfs_get_block ->btrfs_truncate() #alloc truncated blocks #to other inode ->submit_io() #INFORMATION LEAK In order to avoid this problem, we must serialize unlocked dio reads with truncate. There are two approaches: - use extent lock to protect the extent that we truncate - use inode_dio_wait() to make sure the truncating task will wait for the read DIO. If we use the 1st one, we will meet the endless truncation problem due to the nonlocked read DIO after we implement the nonlocked write DIO. It is because we still need invoke inode_dio_wait() avoid the race between write DIO and truncation. By that time, we have to introduce btrfs_inode_{block, resume}_nolock_dio() again. That is we have to implement this patch again, so I choose the 2nd way to fix the problem. Signed-off-by: Miao Xie <miaox@cn.fujitsu.com> Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Diffstat (limited to 'fs/btrfs/btrfs_inode.h')
-rw-r--r--fs/btrfs/btrfs_inode.h19
1 files changed, 19 insertions, 0 deletions
diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index c935a774a9f8..d9b97d4960e6 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -41,6 +41,7 @@
#define BTRFS_INODE_NEEDS_FULL_SYNC 7
#define BTRFS_INODE_COPY_EVERYTHING 8
#define BTRFS_INODE_IN_DELALLOC_LIST 9
+#define BTRFS_INODE_READDIO_NEED_LOCK 10
/* in memory btrfs inode */
struct btrfs_inode {
@@ -217,4 +218,22 @@ static inline int btrfs_inode_in_log(struct inode *inode, u64 generation)
return 0;
}
+/*
+ * Disable DIO read nolock optimization, so new dio readers will be forced
+ * to grab i_mutex. It is used to avoid the endless truncate due to
+ * nonlocked dio read.
+ */
+static inline void btrfs_inode_block_unlocked_dio(struct inode *inode)
+{
+ set_bit(BTRFS_INODE_READDIO_NEED_LOCK, &BTRFS_I(inode)->runtime_flags);
+ smp_mb();
+}
+
+static inline void btrfs_inode_resume_unlocked_dio(struct inode *inode)
+{
+ smp_mb__before_clear_bit();
+ clear_bit(BTRFS_INODE_READDIO_NEED_LOCK,
+ &BTRFS_I(inode)->runtime_flags);
+}
+
#endif