Messages in this thread Patch in this message | | | Subject | Re: [PATCH] xfs: i_state of inode is changed after the inode is freed | From | Masayuki Saito <> | Date | Mon, 24 Jul 2006 17:01:33 +0900 |
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Hi Nathan, David, Thank you for comments.
>I don't think it fixes the problem because igrab() fails to handle >the case we are hitting where I_CLEAR is set on the inode when we >mark it dirty. There's nothing in this patch preventing us from >sleeping after the !(I_NEW|I_FREEING|I_CLEAR) check is done and then >racing with generic_drop_inode() before the igrab() can take a >reference on the inode.
I overlooked the case. Thank you for your review.
>Worse, the i_flags field does not use atomic bitops and >there is no consistent locking protecting i_flags so updates >and reads of this filed can race or even get lost....
I agree it, too. I think that we should add new spin_lock for i_flags.
>I think a fix is going to be much more invasive than just adding >reference as my fixes appear to have only narrowed the race window >and not solved it. The addition of the lock in the original patch >solves the atomic xfs_iunpin()/xfs_reclaim() execution problem, >but it does not solve the problems with the i_flags field. Adding >a new lock may be our only option here.
I'm considering the solution which fixes two problems([a] i_state of the inode is changed while the inode is freed in xfs filesystem and [b] the above i_flags problem)
the solution: (1)Add new spin_lock(i_flags_lock) for all refernece and change places of all i_flags. (2)Add igrab()/iput() for xfs_iunpin().
It makes sure that mark_inode_dirty_sync() is never called if xfs_iunpin() runs after I_CLEAR is set. Because XFS_IRECLAIM or XFS_IRECLAIMABLE is set/checked within the spin_lock.
And there is the reason that igrab()/iput() is needed even if I add new spin_lock for xfs_iunpin(). We can prevent the following case by adding them. * After passing (I_NEW|I_FREEING|I_CLEAR) check in xfs_iunpin(), I_FREEING is set. * Then mark_inode_dirty_sync() is called and i_state is changed. * Hit BUG_ON(!(inode->i_state & I_FREEING)) in clear_inode().
If these ideas seem to be correct, I'll make patches for above (1),(2). Any comment?
(The following is a part of my thinking patch. Only xfs_iunpin().)
--- linux-2.6.17.6/fs/xfs/xfs_inode.c.orig 2006-07-22 08:07:50.194236144 +0900 +++ linux-2.6.17.6/fs/xfs/xfs_inode.c 2006-07-25 06:07:18.062853045 +0900 @@ -2729,6 +2729,8 @@ void xfs_iunpin( xfs_inode_t *ip) { + int need_unlock; + ASSERT(atomic_read(&ip->i_pincount) > 0); if (atomic_dec_and_test(&ip->i_pincount)) { @@ -2744,6 +2746,8 @@ xfs_iunpin( * call as the inode reclaim may be blocked waiting for * the inode to become unpinned. */ + spin_lock(&ip->i_flags_lock); + need_unlock = 1; if (!(ip->i_flags & (XFS_IRECLAIM|XFS_IRECLAIMABLE))) { vnode_t *vp = XFS_ITOV_NULL(ip); @@ -2751,10 +2755,22 @@ xfs_iunpin( if (vp) { struct inode *inode = vn_to_inode(vp); - if (!(inode->i_state & I_NEW)) - mark_inode_dirty_sync(inode); + if (!(inode->i_state & + (I_NEW|I_FREEING|I_CLEAR))) { + inode = igrab(inode); + if (inode != NULL) { + mark_inode_dirty_sync(inode); + spin_unlock(&ip->i_flags_lock); + need_unlock = 0; + iput(inode); + } + } } } + if (need_unlock) { + spin_unlock(&ip->i_flags_lock); + need_unlock = 0; + } wake_up(&ip->i_ipin_wait); } } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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