[PATCH 19/20] XFS: allow follow_link to often succeed in RCU-walk.

NeilBrown
2015-03-23T02:40:00Z

If LOOKUP_RCU is set, use GFP_ATOMIC rather than GFP_KERNEL,
and try to get the ilock without blocking.

When these succeed, follow_link() can succeed without dropping
out of RCU-walk.

As xfs_readlink can now races with xfs_fs_evict_inode:
- xfs_readlink must check if the inode is being evicted after
getting the lock
- xfs_fs_evict_inode cannot assert that the lock is not held.

Signed-off-by: NeilBrown <neilb@suse.de>
---
fs/xfs/xfs_ioctl.c | 2 +-
fs/xfs/xfs_iops.c | 15 ++++++++++-----
fs/xfs/xfs_super.c | 2 --
fs/xfs/xfs_symlink.c | 15 +++++++++++++--
fs/xfs/xfs_symlink.h | 2 +-
5 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index ac4feae45eb3..29d95a1b76c0 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -303,7 +303,7 @@ xfs_readlink_by_handle(
goto out_dput;
}

- error = xfs_readlink(XFS_I(dentry->d_inode), link);
+ error = xfs_readlink(XFS_I(dentry->d_inode), link, 0);
if (error)
goto out_kfree;
error = readlink_copy(hreq->ohandle, olen, link);
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index c2c136ef3a50..631b1ec2e650 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -416,15 +416,20 @@ xfs_vn_follow_link(
int flags)
{
char *link;
- int error = -ENOMEM;
+ int error;

- if (flags & LOOKUP_RCU)
- return ERR_PTR(-ECHILD);
- link = kmalloc(MAXPATHLEN+1, GFP_KERNEL);
+ if (flags & LOOKUP_RCU) {
+ error = -ECHILD;
+ link = kmalloc(MAXPATHLEN+1, GFP_ATOMIC);
+ } else {
+ error = -ENOMEM;
+ link = kmalloc(MAXPATHLEN+1, GFP_KERNEL);
+ }
if (!link)
goto out_err;

- error = xfs_readlink(XFS_I(inode), link);
+ error = xfs_readlink(XFS_I(inode), link,
+ flags & LOOKUP_RCU);
if (unlikely(error))
goto out_kfree;

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 3827be14383c..e041fa55912b 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -996,8 +996,6 @@ xfs_fs_evict_inode(
{
xfs_inode_t *ip = XFS_I(inode);

- ASSERT(!rwsem_is_locked(&ip->i_iolock.mr_lock));
-
trace_xfs_evict_inode(ip);

truncate_inode_pages_final(&inode->i_data);
diff --git a/fs/xfs/xfs_symlink.c b/fs/xfs/xfs_symlink.c
index 25791df6f638..228987b8e758 100644
--- a/fs/xfs/xfs_symlink.c
+++ b/fs/xfs/xfs_symlink.c
@@ -123,7 +123,8 @@ xfs_readlink_bmap(
int
xfs_readlink(
struct xfs_inode *ip,
- char *link)
+ char *link,
+ int rcu)
{
struct xfs_mount *mp = ip->i_mount;
xfs_fsize_t pathlen;
@@ -134,7 +135,15 @@ xfs_readlink(
if (XFS_FORCED_SHUTDOWN(mp))
return -EIO;

- xfs_ilock(ip, XFS_ILOCK_SHARED);
+ if (rcu) {
+ if (xfs_ilock_nowait(ip, XFS_ILOCK_SHARED) == 0)
+ return -ECHILD;
+ if (ip->i_vnode.i_state & (I_FREEING | I_CLEAR)) {
+ xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ return -ECHILD;
+ }
+ } else
+ xfs_ilock(ip, XFS_ILOCK_SHARED);

pathlen = ip->i_d.di_size;
if (!pathlen)
@@ -153,6 +162,8 @@ xfs_readlink(
if (ip->i_df.if_flags & XFS_IFINLINE) {
memcpy(link, ip->i_df.if_u1.if_data, pathlen);
link[pathlen] = '\0';
+ } else if (rcu) {
+ error = -ECHILD;
} else {
error = xfs_readlink_bmap(ip, link);
}
diff --git a/fs/xfs/xfs_symlink.h b/fs/xfs/xfs_symlink.h
index e75245d09116..a71d26643e20 100644
--- a/fs/xfs/xfs_symlink.h
+++ b/fs/xfs/xfs_symlink.h
@@ -21,7 +21,7 @@

int xfs_symlink(struct xfs_inode *dp, struct xfs_name *link_name,
const char *target_path, umode_t mode, struct xfs_inode **ipp);
-int xfs_readlink(struct xfs_inode *ip, char *link);
+int xfs_readlink(struct xfs_inode *ip, char *link, int rcu);
int xfs_inactive_symlink(struct xfs_inode *ip);

#endif /* __XFS_SYMLINK_H */