From: Darrick J. Wong <djwong@xxxxxxxxxx>
I was poking around in the directory code while diagnosing online fsck
bugs, and noticed that xfs_readdir doesn't actually take the directory
ILOCK when it calls xfs_dir2_isblock. xfs_dir_open most probably loaded
the data fork mappings and the VFS took i_rwsem (aka IOLOCK_SHARED) so
we're protected against writer threads, but we really need to follow the
locking model like we do in other places.
To avoid unnecessarily cycling the ILOCK for fairly small directories,
change the block/leaf _getdents functions to consume the ILOCK hold that
the parent readdir function took to decide on a _getdents implementation.
It is ok to cycle the ILOCK in readdir because the VFS takes the IOLOCK
in the appropriate mode during lookups and writes, and we don't want to
be holding the ILOCK when we copy directory entries to userspace in case
there's a page fault. We really only need it to protect against data
fork lookups, like we do for other files.
Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
---
v2: reduce the scope of the locked region, and reduce lock cycling
---
fs/xfs/xfs_dir2_readdir.c | 52 +++++++++++++++++++++++++++++----------------
1 file changed, 33 insertions(+), 19 deletions(-)
diff --git a/fs/xfs/xfs_dir2_readdir.c b/fs/xfs/xfs_dir2_readdir.c
index 8310005af00f..74844edd86a7 100644
--- a/fs/xfs/xfs_dir2_readdir.c
+++ b/fs/xfs/xfs_dir2_readdir.c
@@ -138,7 +138,8 @@ xfs_dir2_sf_getdents(
STATIC int
xfs_dir2_block_getdents(
struct xfs_da_args *args,
- struct dir_context *ctx)
+ struct dir_context *ctx,
+ unsigned int *lock_mode)
{
struct xfs_inode *dp = args->dp; /* incore directory inode */
struct xfs_buf *bp; /* buffer for block */
@@ -146,7 +147,6 @@ xfs_dir2_block_getdents(
int wantoff; /* starting block offset */
xfs_off_t cook;
struct xfs_da_geometry *geo = args->geo;
- int lock_mode;
unsigned int offset, next_offset;
unsigned int end;
@@ -156,12 +156,13 @@ xfs_dir2_block_getdents(
if (xfs_dir2_dataptr_to_db(geo, ctx->pos) > geo->datablk)
return 0;
- lock_mode = xfs_ilock_data_map_shared(dp);
error = xfs_dir3_block_read(args->trans, dp, &bp);
- xfs_iunlock(dp, lock_mode);
if (error)
return error;
+ xfs_iunlock(dp, *lock_mode);
+ *lock_mode = 0;
+
/*
* Extract the byte offset we start at from the seek pointer.
* We'll skip entries before this.
@@ -344,7 +345,8 @@ STATIC int
xfs_dir2_leaf_getdents(
struct xfs_da_args *args,
struct dir_context *ctx,
- size_t bufsize)
+ size_t bufsize,
+ unsigned int *lock_mode)
{
struct xfs_inode *dp = args->dp;
struct xfs_mount *mp = dp->i_mount;
@@ -356,7 +358,6 @@ xfs_dir2_leaf_getdents(
xfs_dir2_off_t curoff; /* current overall offset */
int length; /* temporary length value */
int byteoff; /* offset in current block */
- int lock_mode;
unsigned int offset = 0;
int error = 0; /* error return value */
@@ -390,13 +391,16 @@ xfs_dir2_leaf_getdents(
bp = NULL;
}
- lock_mode = xfs_ilock_data_map_shared(dp);
+ if (*lock_mode == 0)
+ *lock_mode = xfs_ilock_data_map_shared(dp);
error = xfs_dir2_leaf_readbuf(args, bufsize, &curoff,
&rablk, &bp);
- xfs_iunlock(dp, lock_mode);
if (error || !bp)
break;
+ xfs_iunlock(dp, *lock_mode);
+ *lock_mode = 0;
+
xfs_dir3_data_check(dp, bp);
/*
* Find our position in the block.
@@ -507,8 +511,9 @@ xfs_readdir(
size_t bufsize)
{
struct xfs_da_args args = { NULL };
- int rval;
- int v;
+ unsigned int lock_mode;
+ int isblock;
+ int error;
trace_xfs_readdir(dp);
@@ -523,13 +528,22 @@ xfs_readdir(
args.trans = tp;
if (dp->i_df.if_format == XFS_DINODE_FMT_LOCAL)
- rval = xfs_dir2_sf_getdents(&args, ctx);
- else if ((rval = xfs_dir2_isblock(&args, &v)))
- ;
- else if (v)
- rval = xfs_dir2_block_getdents(&args, ctx);
- else
- rval = xfs_dir2_leaf_getdents(&args, ctx, bufsize);
-
- return rval;
+ return xfs_dir2_sf_getdents(&args, ctx);
+
+ lock_mode = xfs_ilock_data_map_shared(dp);
+ error = xfs_dir2_isblock(&args, &isblock);
+ if (error)
+ goto out_unlock;
+
+ if (isblock) {
+ error = xfs_dir2_block_getdents(&args, ctx, &lock_mode);
+ goto out_unlock;
+ }
+
+ error = xfs_dir2_leaf_getdents(&args, ctx, bufsize, &lock_mode);
+
+out_unlock:
+ if (lock_mode)
+ xfs_iunlock(dp, lock_mode);
+ return error;
}
