From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: [PATCH 19/20] XFS: allow follow_link to often succeed in RCU-walk. Date: Mon, 23 Mar 2015 13:37:40 +1100 Message-ID: <20150323023740.8161.44210.stgit@notabene.brown> References: <20150323023258.8161.32467.stgit@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Al Viro Return-path: In-Reply-To: <20150323023258.8161.32467.stgit@notabene.brown> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org 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 --- 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 */