On Wed, Aug 16, 2017 at 10:25:11AM +1000, Dave Chinner wrote: > On Tue, Aug 15, 2017 at 04:29:39PM -0300, Ernesto A. Fernández wrote: > > On Tue, Aug 15, 2017 at 06:44:30PM +1000, Dave Chinner wrote: > > > On Tue, Aug 15, 2017 at 03:18:58AM -0300, Ernesto A. Fernández wrote: > > > But I have to ask - why do we even need to modify the mode first? > > > Why not change the ACL first, then modify the mode+timestamp? If > > > setting the ACL fails, then we don't have anything to undo and all > > > is good.... > > > > I intended for the mode to be committed as part of the same transaction > > that sets or removes the ACL. In my mind making the changes later, as part > > of a separate transaction, would have meant that a crash between the two > > left the filesystem in an inconsistent state, > > No, it will not leave the fileystem in an inconsistent state. It > will leave the inode permissions in an /unwanted/ state, but there > is no filesystem metadata inconsistency. > > > with a new ACL but without > > the corresponding mode bits. > > Yup, but that's no different from right now, where a crash after > setting the mode bits could be applied but the ACL update is > missing. > > Either way is even rarely than "crash at the wrong time" implies, > because we've also got to have a complete journal checkpoint occur > between the two operations and then crash between the checkpoint and > the second operation. Yes, it's possible, but in the entire time > I've been working on XFS (almost 15 years now) I can count on one > hand the number of times such a problem has occurred and been > reported... > > So, it's a rare problem, and one that will get solved in time > because there's much more to solving the problem than just this > case. e.g. I worte this in 2008: > > http://xfs.org/index.php/Improving_Metadata_Performance_By_Reducing_Journal_Overhead#Atomic_Multi-Transaction_Operations > > And we've really only got the infrastructure we could use to > implement this in a widespread manner with the rmap/reflink > functionality. But implementing it will require a large amount of > re-organisation of filesystem operations, so it's something that > will take time to roll out. Alright, thanks for the explanation. > With that in mind, here's waht I suggested above: set the mode after > the xattr. I haven't tested it - can you check it solves the problem > case you are testing? It does. Of course the test still fails, as I said before, now claiming that the filesystem is inconsistent. But that's a separate issue. > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx > > > xfs: don't change inode mode if ACL update fails > > XXX: untested > > --- > fs/xfs/xfs_acl.c | 22 ++++++++++++++++------ > 1 file changed, 16 insertions(+), 6 deletions(-) > > diff --git a/fs/xfs/xfs_acl.c b/fs/xfs/xfs_acl.c > index 7034e17535de..3354140de07e 100644 > --- a/fs/xfs/xfs_acl.c > +++ b/fs/xfs/xfs_acl.c > @@ -247,6 +247,8 @@ xfs_set_mode(struct inode *inode, umode_t mode) > int > xfs_set_acl(struct inode *inode, struct posix_acl *acl, int type) > { > + umode_t mode; > + bool set_mode = false; > int error = 0; > > if (!acl) > @@ -257,16 +259,24 @@ xfs_set_acl(struct inode *inode, struct posix_acl *acl, int type) > return error; > > if (type == ACL_TYPE_ACCESS) { > - umode_t mode; > - > error = posix_acl_update_mode(inode, &mode, &acl); > if (error) > return error; > - error = xfs_set_mode(inode, mode); > - if (error) > - return error; > + set_mode = true; > } > > set_acl: > - return __xfs_set_acl(inode, acl, type); > + error = __xfs_set_acl(inode, acl, type); > + if (error) > + return error; > + > + /* > + * We set the mode after successfully updating the ACL xattr because the > + * xattr update can fail at ENOSPC and we don't want to change the mode > + * if the ACL update hasn't been applied. > + */ > + if (set_mode) > + error = xfs_set_mode(inode, mode); > + > + return error; > } -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
