| Message ID | 20221117025829.GA1095675@ceph-admin (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] xfs: fix incorrect i_nlink caused by inode racing | expand |
On Thu, Nov 17, 2022 at 10:58:29AM +0800, Long Li wrote: > The following error occurred during the fsstress test: > > XFS: Assertion failed: VFS_I(ip)->i_nlink >= 2, file: fs/xfs/xfs_inode.c, line: 2452 > > The problem was that inode race condition causes incorrect i_nlink to be > written to disk, and then it is read into memory. Consider the following > call graph, inodes that are marked as both XFS_IFLUSHING and > XFS_IRECLAIMABLE, i_nlink will be reset to 1 and then restored to original > value in xfs_reinit_inode(). Therefore, the i_nlink of directory on disk > may be set to 1. > > xfsaild > xfs_inode_item_push > xfs_iflush_cluster > xfs_iflush > xfs_inode_to_disk > > xfs_iget > xfs_iget_cache_hit > xfs_iget_recycle > xfs_reinit_inode > inode_init_always > > xfs_reinit_inode() needs to hold the ILOCK_EXCL as it is changing internal > inode state and can race with other RCU protected inode lookups. On the > read side, xfs_iflush_cluster() grabs the ILOCK_SHARED while under rcu + > ip->i_flags_lock, and so xfs_iflush/xfs_inode_to_disk() are protected from > racing inode updates (during transactions) by that lock. > > Signed-off-by: Long Li <leo.lilong@huawei.com> > --- > v2: > - Modify the assertion error code line number > - Use ILOCK_EXCL to prevent inode racing > > fs/xfs/xfs_icache.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c > index eae7427062cf..5a1650e769e7 100644 > --- a/fs/xfs/xfs_icache.c > +++ b/fs/xfs/xfs_icache.c > @@ -329,7 +329,7 @@ xfs_reinit_inode( > > /* > * Carefully nudge an inode whose VFS state has been torn down back into a > - * usable state. Drops the i_flags_lock and the rcu read lock. > + * usable state. Drops the i_flags_lock, rcu read lock and XFS_ILOCK_EXCL. > */ > static int > xfs_iget_recycle( > @@ -355,6 +355,7 @@ xfs_iget_recycle( > > ASSERT(!rwsem_is_locked(&inode->i_rwsem)); > error = xfs_reinit_inode(mp, inode); > + xfs_iunlock(ip, XFS_ILOCK_EXCL); Ugh, please don't take a lock in one function and drop it in a different function. If the trylock is really necessary for this operation, have xfs_iget_recycle return EAGAIN and then make xfs_iget_cache_hit goto out_skip if recycling returns EAGAIN. --D > if (error) { > /* > * Re-initializing the inode failed, and we are in deep > @@ -516,7 +517,10 @@ xfs_iget_cache_hit( > > /* The inode fits the selection criteria; process it. */ > if (ip->i_flags & XFS_IRECLAIMABLE) { > - /* Drops i_flags_lock and RCU read lock. */ > + if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL)) > + goto out_skip; > + > + /* Drops i_flags_lock, RCU read lock and XFS_ILOCK_EXCL. */ > error = xfs_iget_recycle(pag, ip); > if (error) > return error; > -- > 2.31.1 >
diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c index eae7427062cf..5a1650e769e7 100644 --- a/fs/xfs/xfs_icache.c +++ b/fs/xfs/xfs_icache.c @@ -329,7 +329,7 @@ xfs_reinit_inode( /* * Carefully nudge an inode whose VFS state has been torn down back into a - * usable state. Drops the i_flags_lock and the rcu read lock. + * usable state. Drops the i_flags_lock, rcu read lock and XFS_ILOCK_EXCL. */ static int xfs_iget_recycle( @@ -355,6 +355,7 @@ xfs_iget_recycle( ASSERT(!rwsem_is_locked(&inode->i_rwsem)); error = xfs_reinit_inode(mp, inode); + xfs_iunlock(ip, XFS_ILOCK_EXCL); if (error) { /* * Re-initializing the inode failed, and we are in deep @@ -516,7 +517,10 @@ xfs_iget_cache_hit( /* The inode fits the selection criteria; process it. */ if (ip->i_flags & XFS_IRECLAIMABLE) { - /* Drops i_flags_lock and RCU read lock. */ + if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL)) + goto out_skip; + + /* Drops i_flags_lock, RCU read lock and XFS_ILOCK_EXCL. */ error = xfs_iget_recycle(pag, ip); if (error) return error;
The following error occurred during the fsstress test: XFS: Assertion failed: VFS_I(ip)->i_nlink >= 2, file: fs/xfs/xfs_inode.c, line: 2452 The problem was that inode race condition causes incorrect i_nlink to be written to disk, and then it is read into memory. Consider the following call graph, inodes that are marked as both XFS_IFLUSHING and XFS_IRECLAIMABLE, i_nlink will be reset to 1 and then restored to original value in xfs_reinit_inode(). Therefore, the i_nlink of directory on disk may be set to 1. xfsaild xfs_inode_item_push xfs_iflush_cluster xfs_iflush xfs_inode_to_disk xfs_iget xfs_iget_cache_hit xfs_iget_recycle xfs_reinit_inode inode_init_always xfs_reinit_inode() needs to hold the ILOCK_EXCL as it is changing internal inode state and can race with other RCU protected inode lookups. On the read side, xfs_iflush_cluster() grabs the ILOCK_SHARED while under rcu + ip->i_flags_lock, and so xfs_iflush/xfs_inode_to_disk() are protected from racing inode updates (during transactions) by that lock. Signed-off-by: Long Li <leo.lilong@huawei.com> --- v2: - Modify the assertion error code line number - Use ILOCK_EXCL to prevent inode racing fs/xfs/xfs_icache.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)