Ocfs2 devel - Oct 2017 - [PATCH v2] ocfs2: the ip_alloc_sem should be taken in ocfs2_get_block()

The ip_alloc_sem should be taken in ocfs2_get_block() when reading file
in DIRECT mode to prevent concurrent access to extent tree with
ocfs2_dio_end_io_write(), which may cause BUGON in
ocfs2_get_clusters_nocache()->BUG_ON(v_cluster <
le32_to_cpu(rec->e_cpos))

Fixes: c15471f79506 ("ocfs2: fix sparse file & data ordering issue in
direct io")

Signed-off-by: Alex Chen <alex.chen at huawei.com>
Reviewed-by: Jun Piao <piaojun at huawei.com>
Acked-by: Changwei Ge <ge.changwei at h3c.com>

---
 fs/ocfs2/aops.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index 88a31e9..29607d9 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -134,6 +134,19 @@ static int ocfs2_symlink_get_block(struct inode *inode,
sector_t iblock,
 	return err;
 }

+static int ocfs2_get_block_lock(struct inode *inode, sector_t iblock,
+		    struct buffer_head *bh_result, int create)
+{
+	int ret = 0;
+	struct ocfs2_inode_info *oi = OCFS2_I(inode);
+
+	down_read(&oi->ip_alloc_sem);
+	ret = ocfs2_get_block(inode, iblock, bh_result, create);
+	up_read(&oi->ip_alloc_sem);
+
+	return ret;
+}
+
 int ocfs2_get_block(struct inode *inode, sector_t iblock,
 		    struct buffer_head *bh_result, int create)
 {
@@ -2154,12 +2167,9 @@ static int ocfs2_dio_get_block(struct inode *inode,
sector_t iblock,
 	 * while file size will be changed.
 	 */
 	if (pos + total_len <= i_size_read(inode)) {
-		down_read(&oi->ip_alloc_sem);
-		/* This is the fast path for re-write. */
-		ret = ocfs2_get_block(inode, iblock, bh_result, create);
-
-		up_read(&oi->ip_alloc_sem);

+		/* This is the fast path for re-write. */
+		ret = ocfs2_get_block_lock(inode, iblock, bh_result, create);
 		if (buffer_mapped(bh_result) &&
 		    !buffer_new(bh_result) &&
 		    ret == 0)
@@ -2424,7 +2434,7 @@ static ssize_t ocfs2_direct_IO(struct kiocb *iocb, struct
iov_iter *iter)
 		return 0;

 	if (iov_iter_rw(iter) == READ)
-		get_block = ocfs2_get_block;
+		get_block = ocfs2_get_block_lock;
 	else
 		get_block = ocfs2_dio_get_block;

-- 
1.9.5.msysgit.1

Hello Alex,

Base on your bug description, I think that the fix should be OK.
But I suggest you to use more clear function name in this patch.
1) For new-added function ocfs2_get_block_lock(), I think that it is better if
the function name is ocfs2_dio_rd_get_block().
2) Then, rename the original function ocfs2_dio_get_block() to
ocfs2_dio_wr_get_block().
Why? 
Since this function looks to only be used by direct IO (read) mode, 
we should make the function name more clear, do NOT make other developer to
misunderstand/misuse it in the future.

Thanks
Gang 

>>> 
> The ip_alloc_sem should be taken in ocfs2_get_block() when reading file
> in DIRECT mode to prevent concurrent access to extent tree with
> ocfs2_dio_end_io_write(), which may cause BUGON in
> ocfs2_get_clusters_nocache()->BUG_ON(v_cluster <
le32_to_cpu(rec->e_cpos))
> 
> Fixes: c15471f79506 ("ocfs2: fix sparse file & data ordering issue
in direct
> io")
> 
> Signed-off-by: Alex Chen <alex.chen at huawei.com>
> Reviewed-by: Jun Piao <piaojun at huawei.com>
> Acked-by: Changwei Ge <ge.changwei at h3c.com>
> 
> ---
>  fs/ocfs2/aops.c | 22 ++++++++++++++++------
>  1 file changed, 16 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
> index 88a31e9..29607d9 100644
> --- a/fs/ocfs2/aops.c
> +++ b/fs/ocfs2/aops.c
> @@ -134,6 +134,19 @@ static int ocfs2_symlink_get_block(struct inode
*inode,
> sector_t iblock,
>  	return err;
>  }
> 
> +static int ocfs2_get_block_lock(struct inode *inode, sector_t iblock,
> +		    struct buffer_head *bh_result, int create)
> +{
> +	int ret = 0;
> +	struct ocfs2_inode_info *oi = OCFS2_I(inode);
> +
> +	down_read(&oi->ip_alloc_sem);
> +	ret = ocfs2_get_block(inode, iblock, bh_result, create);
> +	up_read(&oi->ip_alloc_sem);
> +
> +	return ret;
> +}
> +
>  int ocfs2_get_block(struct inode *inode, sector_t iblock,
>  		    struct buffer_head *bh_result, int create)
>  {
> @@ -2154,12 +2167,9 @@ static int ocfs2_dio_get_block(struct inode *inode, 
> sector_t iblock,
>  	 * while file size will be changed.
>  	 */
>  	if (pos + total_len <= i_size_read(inode)) {
> -		down_read(&oi->ip_alloc_sem);
> -		/* This is the fast path for re-write. */
> -		ret = ocfs2_get_block(inode, iblock, bh_result, create);
> -
> -		up_read(&oi->ip_alloc_sem);
> 
> +		/* This is the fast path for re-write. */
> +		ret = ocfs2_get_block_lock(inode, iblock, bh_result, create);
>  		if (buffer_mapped(bh_result) &&
>  		    !buffer_new(bh_result) &&
>  		    ret == 0)
> @@ -2424,7 +2434,7 @@ static ssize_t ocfs2_direct_IO(struct kiocb *iocb, 
> struct iov_iter *iter)
>  		return 0;
> 
>  	if (iov_iter_rw(iter) == READ)
> -		get_block = ocfs2_get_block;
> +		get_block = ocfs2_get_block_lock;
>  	else
>  		get_block = ocfs2_dio_get_block;
> 
> -- 
> 1.9.5.msysgit.1
> 
> 
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