Commit bc990f5c authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Felix Blyakher
Browse files

xfs: fix locking in xfs_iget_cache_hit 



The locking in xfs_iget_cache_hit currently has numerous problems:

 - we clear the reclaim tag without i_flags_lock which protects
   modifications to it
 - we call inode_init_always which can sleep with pag_ici_lock
   held (this is oss.sgi.com BZ #819)
 - we acquire and drop i_flags_lock a lot and thus provide no
   consistency between the various flags we set/clear under it

This patch fixes all that with a major revamp of the locking in
the function.  The new version acquires i_flags_lock early and
only drops it once we need to call into inode_init_always or before
calling xfs_ilock.

This patch fixes a bug seen in the wild where we race modifying the
reclaim tag.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarFelix Blyakher <felixb@sgi.com>
Reviewed-by: default avatarEric Sandeen <sandeen@sandeen.net>
Signed-off-by: default avatarFelix Blyakher <felixb@sgi.com>
parent 894ef820

fs/xfs/linux-2.6/xfs_sync.c

+11 −2
Original line number Diff line number Diff line
@@ -708,6 +708,16 @@ xfs_reclaim_inode( 
	return 0;

}



void

__xfs_inode_set_reclaim_tag(

	struct xfs_perag	*pag,

	struct xfs_inode	*ip)

{

	radix_tree_tag_set(&pag->pag_ici_root,

			   XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino),

			   XFS_ICI_RECLAIM_TAG);

}



/*

 * We set the inode flag atomically with the radix tree tag.

 * Once we get tag lookups on the radix tree, this inode flag
@@ -722,8 +732,7 @@ xfs_inode_set_reclaim_tag( 


	read_lock(&pag->pag_ici_lock);

	spin_lock(&ip->i_flags_lock);

	radix_tree_tag_set(&pag->pag_ici_root,

			XFS_INO_TO_AGINO(mp, ip->i_ino), XFS_ICI_RECLAIM_TAG);

	__xfs_inode_set_reclaim_tag(pag, ip);

	__xfs_iflags_set(ip, XFS_IRECLAIMABLE);

	spin_unlock(&ip->i_flags_lock);

	read_unlock(&pag->pag_ici_lock);

fs/xfs/linux-2.6/xfs_sync.h

+1 −0
Original line number Diff line number Diff line
@@ -48,6 +48,7 @@ int xfs_reclaim_inode(struct xfs_inode *ip, int locked, int sync_mode); 
int xfs_reclaim_inodes(struct xfs_mount *mp, int mode);



void xfs_inode_set_reclaim_tag(struct xfs_inode *ip);

void __xfs_inode_set_reclaim_tag(struct xfs_perag *pag, struct xfs_inode *ip);

void xfs_inode_clear_reclaim_tag(struct xfs_inode *ip);

void __xfs_inode_clear_reclaim_tag(struct xfs_mount *mp, struct xfs_perag *pag,

				struct xfs_inode *ip);

fs/xfs/xfs_iget.c

+58 −55
Original line number Diff line number Diff line
@@ -191,79 +191,81 @@ xfs_iget_cache_hit( 
	int			flags,

	int			lock_flags) __releases(pag->pag_ici_lock)

{

	struct inode		*inode = VFS_I(ip);

	struct xfs_mount	*mp = ip->i_mount;

	int			error = EAGAIN;

	int			error;



	spin_lock(&ip->i_flags_lock);



	/*

	 * If INEW is set this inode is being set up

	 * If IRECLAIM is set this inode is being torn down

	 * Pause and try again.

	 * If we are racing with another cache hit that is currently

	 * instantiating this inode or currently recycling it out of

	 * reclaimabe state, wait for the initialisation to complete

	 * before continuing.

	 *

	 * XXX(hch): eventually we should do something equivalent to

	 *	     wait_on_inode to wait for these flags to be cleared

	 *	     instead of polling for it.

	 */

	if (xfs_iflags_test(ip, (XFS_INEW|XFS_IRECLAIM))) {

	if (ip->i_flags & (XFS_INEW|XFS_IRECLAIM)) {

		XFS_STATS_INC(xs_ig_frecycle);

		error = EAGAIN;

		goto out_error;

	}



	/* If IRECLAIMABLE is set, we've torn down the vfs inode part */

	if (xfs_iflags_test(ip, XFS_IRECLAIMABLE)) {



	/*

		 * If lookup is racing with unlink, then we should return an

		 * error immediately so we don't remove it from the reclaim

		 * list and potentially leak the inode.

	 * If lookup is racing with unlink return an error immediately.

	 */

		if ((ip->i_d.di_mode == 0) && !(flags & XFS_IGET_CREATE)) {

	if (ip->i_d.di_mode == 0 && !(flags & XFS_IGET_CREATE)) {

		error = ENOENT;

		goto out_error;

	}



	/*

	 * If IRECLAIMABLE is set, we've torn down the VFS inode already.

	 * Need to carefully get it back into useable state.

	 */

	if (ip->i_flags & XFS_IRECLAIMABLE) {

		xfs_itrace_exit_tag(ip, "xfs_iget.alloc");



		/*

		 * We need to re-initialise the VFS inode as it has been

		 * 'freed' by the VFS. Do this here so we can deal with

		 * errors cleanly, then tag it so it can be set up correctly

		 * later.

		 * We need to set XFS_INEW atomically with clearing the

		 * reclaimable tag so that we do have an indicator of the

		 * inode still being initialized.

		 */

		if (inode_init_always(mp->m_super, VFS_I(ip))) {

			error = ENOMEM;

			goto out_error;

		}

		ip->i_flags |= XFS_INEW;

		ip->i_flags &= ~XFS_IRECLAIMABLE;

		__xfs_inode_clear_reclaim_tag(mp, pag, ip);



		spin_unlock(&ip->i_flags_lock);

		read_unlock(&pag->pag_ici_lock);



		error = -inode_init_always(mp->m_super, inode);

		if (error) {

			/*

		 * We must set the XFS_INEW flag before clearing the

		 * XFS_IRECLAIMABLE flag so that if a racing lookup does

		 * not find the XFS_IRECLAIMABLE above but has the igrab()

		 * below succeed we can safely check XFS_INEW to detect

		 * that this inode is still being initialised.

			 * Re-initializing the inode failed, and we are in deep

			 * trouble.  Try to re-add it to the reclaim list.

			 */

		xfs_iflags_set(ip, XFS_INEW);

		xfs_iflags_clear(ip, XFS_IRECLAIMABLE);

			read_lock(&pag->pag_ici_lock);

			spin_lock(&ip->i_flags_lock);



		/* clear the radix tree reclaim flag as well. */

		__xfs_inode_clear_reclaim_tag(mp, pag, ip);

	} else if (!igrab(VFS_I(ip))) {

		/* If the VFS inode is being torn down, pause and try again. */

		XFS_STATS_INC(xs_ig_frecycle);

			ip->i_flags &= ~XFS_INEW;

			ip->i_flags |= XFS_IRECLAIMABLE;

			__xfs_inode_set_reclaim_tag(pag, ip);

			goto out_error;

	} else if (xfs_iflags_test(ip, XFS_INEW)) {

		/*

		 * We are racing with another cache hit that is

		 * currently recycling this inode out of the XFS_IRECLAIMABLE

		 * state. Wait for the initialisation to complete before

		 * continuing.

		 */

		wait_on_inode(VFS_I(ip));

		}



	if (ip->i_d.di_mode == 0 && !(flags & XFS_IGET_CREATE)) {

		error = ENOENT;

		iput(VFS_I(ip));

		inode->i_state = I_LOCK|I_NEW;

	} else {

		/* If the VFS inode is being torn down, pause and try again. */

		if (!igrab(inode)) {

			error = EAGAIN;

			goto out_error;

		}



		/* We've got a live one. */

		spin_unlock(&ip->i_flags_lock);

		read_unlock(&pag->pag_ici_lock);

	}



	if (lock_flags != 0)

		xfs_ilock(ip, lock_flags);
@@ -274,6 +276,7 @@ xfs_iget_cache_hit( 
	return 0;



out_error:

	spin_unlock(&ip->i_flags_lock);

	read_unlock(&pag->pag_ici_lock);

	return error;

}

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