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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: Christoph Hellwig <hch@lst.de> Reviewed-by: Felix Blyakher <felixb@sgi.com> Reviewed-by: Eric Sandeen <sandeen@sandeen.net> Signed-off-by: Felix Blyakher <felixb@sgi.com>
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894ef820b1
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bc990f5cb4
@ -708,6 +708,16 @@ xfs_reclaim_inode(
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return 0;
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}
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void
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__xfs_inode_set_reclaim_tag(
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struct xfs_perag *pag,
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struct xfs_inode *ip)
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{
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radix_tree_tag_set(&pag->pag_ici_root,
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XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino),
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XFS_ICI_RECLAIM_TAG);
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}
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/*
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* We set the inode flag atomically with the radix tree tag.
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* Once we get tag lookups on the radix tree, this inode flag
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@ -722,8 +732,7 @@ xfs_inode_set_reclaim_tag(
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read_lock(&pag->pag_ici_lock);
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spin_lock(&ip->i_flags_lock);
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radix_tree_tag_set(&pag->pag_ici_root,
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XFS_INO_TO_AGINO(mp, ip->i_ino), XFS_ICI_RECLAIM_TAG);
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__xfs_inode_set_reclaim_tag(pag, ip);
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__xfs_iflags_set(ip, XFS_IRECLAIMABLE);
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spin_unlock(&ip->i_flags_lock);
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read_unlock(&pag->pag_ici_lock);
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@ -48,6 +48,7 @@ int xfs_reclaim_inode(struct xfs_inode *ip, int locked, int sync_mode);
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int xfs_reclaim_inodes(struct xfs_mount *mp, int mode);
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void xfs_inode_set_reclaim_tag(struct xfs_inode *ip);
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void __xfs_inode_set_reclaim_tag(struct xfs_perag *pag, struct xfs_inode *ip);
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void xfs_inode_clear_reclaim_tag(struct xfs_inode *ip);
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void __xfs_inode_clear_reclaim_tag(struct xfs_mount *mp, struct xfs_perag *pag,
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struct xfs_inode *ip);
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@ -191,80 +191,82 @@ xfs_iget_cache_hit(
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int flags,
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int lock_flags) __releases(pag->pag_ici_lock)
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{
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struct inode *inode = VFS_I(ip);
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struct xfs_mount *mp = ip->i_mount;
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int error = EAGAIN;
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int error;
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spin_lock(&ip->i_flags_lock);
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/*
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* If INEW is set this inode is being set up
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* If IRECLAIM is set this inode is being torn down
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* Pause and try again.
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* If we are racing with another cache hit that is currently
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* instantiating this inode or currently recycling it out of
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* reclaimabe state, wait for the initialisation to complete
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* before continuing.
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*
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* XXX(hch): eventually we should do something equivalent to
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* wait_on_inode to wait for these flags to be cleared
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* instead of polling for it.
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*/
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if (xfs_iflags_test(ip, (XFS_INEW|XFS_IRECLAIM))) {
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if (ip->i_flags & (XFS_INEW|XFS_IRECLAIM)) {
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XFS_STATS_INC(xs_ig_frecycle);
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error = EAGAIN;
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goto out_error;
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}
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/* If IRECLAIMABLE is set, we've torn down the vfs inode part */
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if (xfs_iflags_test(ip, XFS_IRECLAIMABLE)) {
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/*
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* If lookup is racing with unlink, then we should return an
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* error immediately so we don't remove it from the reclaim
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* list and potentially leak the inode.
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*/
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if ((ip->i_d.di_mode == 0) && !(flags & XFS_IGET_CREATE)) {
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error = ENOENT;
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goto out_error;
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}
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/*
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* If lookup is racing with unlink return an error immediately.
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*/
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if (ip->i_d.di_mode == 0 && !(flags & XFS_IGET_CREATE)) {
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error = ENOENT;
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goto out_error;
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}
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/*
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* If IRECLAIMABLE is set, we've torn down the VFS inode already.
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* Need to carefully get it back into useable state.
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*/
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if (ip->i_flags & XFS_IRECLAIMABLE) {
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xfs_itrace_exit_tag(ip, "xfs_iget.alloc");
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/*
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* We need to re-initialise the VFS inode as it has been
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* 'freed' by the VFS. Do this here so we can deal with
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* errors cleanly, then tag it so it can be set up correctly
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* later.
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* We need to set XFS_INEW atomically with clearing the
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* reclaimable tag so that we do have an indicator of the
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* inode still being initialized.
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*/
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if (inode_init_always(mp->m_super, VFS_I(ip))) {
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error = ENOMEM;
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ip->i_flags |= XFS_INEW;
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ip->i_flags &= ~XFS_IRECLAIMABLE;
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__xfs_inode_clear_reclaim_tag(mp, pag, ip);
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spin_unlock(&ip->i_flags_lock);
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read_unlock(&pag->pag_ici_lock);
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error = -inode_init_always(mp->m_super, inode);
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if (error) {
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/*
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* Re-initializing the inode failed, and we are in deep
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* trouble. Try to re-add it to the reclaim list.
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*/
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read_lock(&pag->pag_ici_lock);
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spin_lock(&ip->i_flags_lock);
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ip->i_flags &= ~XFS_INEW;
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ip->i_flags |= XFS_IRECLAIMABLE;
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__xfs_inode_set_reclaim_tag(pag, ip);
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goto out_error;
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}
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inode->i_state = I_LOCK|I_NEW;
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} else {
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/* If the VFS inode is being torn down, pause and try again. */
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if (!igrab(inode)) {
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error = EAGAIN;
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goto out_error;
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}
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/*
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* We must set the XFS_INEW flag before clearing the
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* XFS_IRECLAIMABLE flag so that if a racing lookup does
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* not find the XFS_IRECLAIMABLE above but has the igrab()
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* below succeed we can safely check XFS_INEW to detect
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* that this inode is still being initialised.
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*/
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xfs_iflags_set(ip, XFS_INEW);
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xfs_iflags_clear(ip, XFS_IRECLAIMABLE);
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/* clear the radix tree reclaim flag as well. */
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__xfs_inode_clear_reclaim_tag(mp, pag, ip);
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} else if (!igrab(VFS_I(ip))) {
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/* If the VFS inode is being torn down, pause and try again. */
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XFS_STATS_INC(xs_ig_frecycle);
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goto out_error;
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} else if (xfs_iflags_test(ip, XFS_INEW)) {
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/*
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* We are racing with another cache hit that is
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* currently recycling this inode out of the XFS_IRECLAIMABLE
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* state. Wait for the initialisation to complete before
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* continuing.
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*/
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wait_on_inode(VFS_I(ip));
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/* We've got a live one. */
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spin_unlock(&ip->i_flags_lock);
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read_unlock(&pag->pag_ici_lock);
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}
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if (ip->i_d.di_mode == 0 && !(flags & XFS_IGET_CREATE)) {
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error = ENOENT;
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iput(VFS_I(ip));
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goto out_error;
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}
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/* We've got a live one. */
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read_unlock(&pag->pag_ici_lock);
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if (lock_flags != 0)
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xfs_ilock(ip, lock_flags);
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@ -274,6 +276,7 @@ xfs_iget_cache_hit(
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return 0;
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out_error:
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spin_unlock(&ip->i_flags_lock);
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read_unlock(&pag->pag_ici_lock);
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return error;
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}
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