[PATCH 2/2] xfs: stop holding ILOCK over filldir callbacks

Dave Chinner
2015-08-11T22:04:44Z

From: Dave Chinner <dchinner@redhat.com>

The recent change to the readdir locking made in 40194ec ("xfs:
reinstate the ilock in xfs_readdir") for CXFS directory sanity was
probably the wrong thing to do. Deep in the readdir code we
can take page faults in the filldir callback, and so taking a page
fault while holding an inode ilock creates a new set of locking
issues that lockdep warns all over the place about.

The locking order for regular inodes w.r.t. page faults is io_lock
-> pagefault -> mmap_sem -> ilock. The directory readdir code now
triggers ilock -> page fault -> mmap_sem. While we cannot deadlock
at this point, it inverts all the locking patterns that lockdep
normally sees on XFS inodes, and so triggers lockdep. We worked
around this with commit 93a8614 ("xfs: fix directory inode iolock
lockdep false positive"), but that then just moved the lockdep
warning to deeper in the page fault path and triggered on security
inode locks. Fixing the shmem issue there just moved the lockdep
reports somewhere else, and now we are getting false positives from
filesystem freezing annotations getting confused.

Further, if we enter memory reclaim in a readdir path, we now get
lockdep warning about potential deadlocks because the ilock is held
when we enter reclaim. This, again, is different to a regular file
in that we never allow memory reclaim to run while holding the ilock
for regular files. Hence lockdep now throws
ilock->kmalloc->reclaim->ilock warnings.

Basically, the problem is that the ilock is being used to protect
the directory data and the inode metadata, whereas for a regular
file the iolock protects the data and the ilock protects the
metadata. From the VFS perspective, the i_mutex serialises all
accesses to the directory data, and so not holding the ilock for
readdir doesn't matter. The issue is that CXFS doesn't access
directory data via the VFS, so it has no "data serialisaton"
mechanism. Hence we need to hold the IOLOCK in the correct places to
provide this low level directory data access serialisation.

The ilock can then be used just when the extent list needs to be
read, just like we do for regular files. The directory modification
code can take the iolock exclusive when the ilock is also taken,
and this then ensures that readdir is correct excluded while
modifications are in progress.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/libxfs/xfs_dir2.c | 3 +++
fs/xfs/xfs_dir2_readdir.c | 11 ++++++++---
fs/xfs/xfs_inode.c | 34 +++++++++++++++++++++-------------
fs/xfs/xfs_symlink.c | 7 ++++---
4 files changed, 36 insertions(+), 19 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_dir2.c b/fs/xfs/libxfs/xfs_dir2.c
index a69fb3a..42799d8 100644
--- a/fs/xfs/libxfs/xfs_dir2.c
+++ b/fs/xfs/libxfs/xfs_dir2.c
@@ -362,6 +362,7 @@ xfs_dir_lookup(
struct xfs_da_args *args;
int rval;
int v; /* type-checking value */
+ int lock_mode;

ASSERT(S_ISDIR(dp->i_d.di_mode));
XFS_STATS_INC(xs_dir_lookup);
@@ -387,6 +388,7 @@ xfs_dir_lookup(
if (ci_name)
args->op_flags |= XFS_DA_OP_CILOOKUP;

+ lock_mode = xfs_ilock_data_map_shared(dp);
if (dp->i_d.di_format == XFS_DINODE_FMT_LOCAL) {
rval = xfs_dir2_sf_lookup(args);
goto out_check_rval;
@@ -419,6 +421,7 @@ out_check_rval:
}
}
out_free:
+ xfs_iunlock(dp, lock_mode);
kmem_free(args);
return rval;
}
diff --git a/fs/xfs/xfs_dir2_readdir.c b/fs/xfs/xfs_dir2_readdir.c
index 098cd78..a989a9c 100644
--- a/fs/xfs/xfs_dir2_readdir.c
+++ b/fs/xfs/xfs_dir2_readdir.c
@@ -171,6 +171,7 @@ xfs_dir2_block_getdents(
int wantoff; /* starting block offset */
xfs_off_t cook;
struct xfs_da_geometry *geo = args->geo;
+ int lock_mode;

/*
* If the block number in the offset is out of range, we're done.
@@ -178,7 +179,9 @@ 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(NULL, dp, &bp);
+ xfs_iunlock(dp, lock_mode);
if (error)
return error;

@@ -529,9 +532,12 @@ xfs_dir2_leaf_getdents(
* current buffer, need to get another one.
*/
if (!bp || ptr >= (char *)bp->b_addr + geo->blksize) {
+ int lock_mode;

+ lock_mode = xfs_ilock_data_map_shared(dp);
error = xfs_dir2_leaf_readbuf(args, bufsize, map_info,
&curoff, &bp);
+ xfs_iunlock(dp, lock_mode);
if (error || !map_info->map_valid)
break;

@@ -653,7 +659,6 @@ xfs_readdir(
struct xfs_da_args args = { NULL };
int rval;
int v;
- uint lock_mode;

trace_xfs_readdir(dp);

@@ -666,7 +671,7 @@ xfs_readdir(
args.dp = dp;
args.geo = dp->i_mount->m_dir_geo;

- lock_mode = xfs_ilock_data_map_shared(dp);
+ xfs_ilock(dp, XFS_IOLOCK_SHARED);
if (dp->i_d.di_format == XFS_DINODE_FMT_LOCAL)
rval = xfs_dir2_sf_getdents(&args, ctx);
else if ((rval = xfs_dir2_isblock(&args, &v)))
@@ -675,7 +680,7 @@ xfs_readdir(
rval = xfs_dir2_block_getdents(&args, ctx);
else
rval = xfs_dir2_leaf_getdents(&args, ctx, bufsize);
- xfs_iunlock(dp, lock_mode);
+ xfs_iunlock(dp, XFS_IOLOCK_SHARED);

return rval;
}
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 793e6c9..83b0752 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -672,30 +672,29 @@ xfs_lookup(
{
xfs_ino_t inum;
int error;
- uint lock_mode;

trace_xfs_lookup(dp, name);

if (XFS_FORCED_SHUTDOWN(dp->i_mount))
return -EIO;

- lock_mode = xfs_ilock_data_map_shared(dp);
+ xfs_ilock(dp, XFS_IOLOCK_SHARED);
error = xfs_dir_lookup(NULL, dp, name, &inum, ci_name);
- xfs_iunlock(dp, lock_mode);
-
if (error)
- goto out;
+ goto out_unlock;

error = xfs_iget(dp->i_mount, NULL, inum, 0, 0, ipp);
if (error)
goto out_free_name;

+ xfs_iunlock(dp, XFS_IOLOCK_SHARED);
return 0;

out_free_name:
if (ci_name)
kmem_free(ci_name->name);
-out:
+out_unlock:
+ xfs_iunlock(dp, XFS_IOLOCK_SHARED);
*ipp = NULL;
return error;
}
@@ -1197,7 +1196,8 @@ xfs_create(
goto out_trans_cancel;

- xfs_ilock(dp, XFS_ILOCK_EXCL | XFS_ILOCK_PARENT);
+ xfs_ilock(dp, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL |
+ XFS_IOLOCK_PARENT | XFS_ILOCK_PARENT);
unlock_dp_on_error = true;

xfs_bmap_init(&free_list, &first_block);
@@ -1236,7 +1236,7 @@ xfs_create(
* the transaction cancel unlocking dp so don't do it explicitly in the
* error path.
*/
- xfs_trans_ijoin(tp, dp, XFS_ILOCK_EXCL);
+ xfs_trans_ijoin(tp, dp, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL);
unlock_dp_on_error = false;

error = xfs_dir_createname(tp, dp, name, ip->i_ino,
@@ -1309,7 +1309,7 @@ xfs_create(
xfs_qm_dqrele(pdqp);

if (unlock_dp_on_error)
- xfs_iunlock(dp, XFS_ILOCK_EXCL);
+ xfs_iunlock(dp, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL);
return error;
}

@@ -1457,10 +1457,11 @@ xfs_link(
if (error)
goto error_return;

+ xfs_ilock(tdp, XFS_IOLOCK_EXCL | XFS_IOLOCK_PARENT);
xfs_lock_two_inodes(sip, tdp, XFS_ILOCK_EXCL);

xfs_trans_ijoin(tp, sip, XFS_ILOCK_EXCL);
- xfs_trans_ijoin(tp, tdp, XFS_ILOCK_EXCL);
+ xfs_trans_ijoin(tp, tdp, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL);

/*
* If we are using project inheritance, we only allow hard link
@@ -2563,9 +2564,10 @@ xfs_remove(
goto out_trans_cancel;
}

+ xfs_ilock(dp, XFS_IOLOCK_EXCL | XFS_IOLOCK_PARENT);
xfs_lock_two_inodes(dp, ip, XFS_ILOCK_EXCL);

- xfs_trans_ijoin(tp, dp, XFS_ILOCK_EXCL);
+ xfs_trans_ijoin(tp, dp, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL);
xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);

/*
@@ -2946,6 +2948,12 @@ xfs_rename(
* whether the target directory is the same as the source
* directory, we can lock from 2 to 4 inodes.
*/
+ if (!new_parent)
+ xfs_ilock(src_dp, XFS_IOLOCK_EXCL | XFS_IOLOCK_PARENT);
+ else
+ xfs_lock_two_inodes(src_dp, target_dp,
+ XFS_IOLOCK_EXCL | XFS_IOLOCK_PARENT);
+
xfs_lock_inodes(inodes, num_inodes, XFS_ILOCK_EXCL);

/*
@@ -2953,9 +2961,9 @@ xfs_rename(
* we can rely on either trans_commit or trans_cancel to unlock
* them.
*/
- xfs_trans_ijoin(tp, src_dp, XFS_ILOCK_EXCL);
+ xfs_trans_ijoin(tp, src_dp, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL);
if (new_parent)
- xfs_trans_ijoin(tp, target_dp, XFS_ILOCK_EXCL);
+ xfs_trans_ijoin(tp, target_dp, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL);
xfs_trans_ijoin(tp, src_ip, XFS_ILOCK_EXCL);
if (target_ip)
xfs_trans_ijoin(tp, target_ip, XFS_ILOCK_EXCL);
diff --git a/fs/xfs/xfs_symlink.c b/fs/xfs/xfs_symlink.c
index 4be27b0..7a01486 100644
--- a/fs/xfs/xfs_symlink.c
+++ b/fs/xfs/xfs_symlink.c
@@ -240,7 +240,8 @@ xfs_symlink(
if (error)
goto out_trans_cancel;

- xfs_ilock(dp, XFS_ILOCK_EXCL | XFS_ILOCK_PARENT);
+ xfs_ilock(dp, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL |
+ XFS_IOLOCK_PARENT | XFS_ILOCK_PARENT);
unlock_dp_on_error = true;

/*
@@ -288,7 +289,7 @@ xfs_symlink(
* the transaction cancel unlocking dp so don't do it explicitly in the
* error path.
*/
- xfs_trans_ijoin(tp, dp, XFS_ILOCK_EXCL);
+ xfs_trans_ijoin(tp, dp, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL);
unlock_dp_on_error = false;

/*
@@ -421,7 +422,7 @@ out_release_inode:
xfs_qm_dqrele(pdqp);

if (unlock_dp_on_error)
- xfs_iunlock(dp, XFS_ILOCK_EXCL);
+ xfs_iunlock(dp, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL);
return error;
}

--
2.5.0