On Tue 25-04-17 06:35:13, Jeff Layton wrote: > On Tue, 2017-04-25 at 10:17 +0200, Jan Kara wrote: > > On Mon 24-04-17 13:14:36, Jeff Layton wrote: > > > On Mon, 2017-04-24 at 18:04 +0200, Jan Kara wrote: > > > > On Mon 24-04-17 09:22:49, Jeff Layton wrote: > > > > > This ensures that we see errors on fsync when writeback fails. > > > > > > > > > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > > > > > > > > Hum, but do we really want to clobber mapping errors with temporary stuff > > > > like ENOMEM? Or do you want to handle that in mapping_set_error? > > > > > > > > > > Right now we don't really have such a thing as temporary errors in the > > > writeback codepath. If you return an error here, the data doesn't stay > > > dirty or anything, and I think we want to ensure that that gets reported > > > via fsync. > > > > > > I'd like to see us add better handling for retryable errors for stuff > > > like ENOMEM or EAGAIN. I think this is the first step toward that > > > though. Once we have more consistent handling of writeback errors in > > > general, then we can start doing more interesting things with retryable > > > errors. > > > > > > So yeah, I this is the right thing to do for now. > > > > OK, fair enough. And question number 2): > > > > Who is actually responsible for setting the error in the mapping when error > > happens inside ->writepage()? Is it the ->writepage() callback or the > > caller of ->writepage()? Or something else? Currently it seems to be a > > strange mix (e.g. mm/page-writeback.c: __writepage() calls > > mapping_set_error() when ->writepage() returns error) so I'd like to > > understand what's the plan and have that recorded in the changelogs. > > > > That's an excellent question. > > I think we probably want the writepage/launder_page operations to call > mapping_set_error. That makes it possible for filesystems (e.g. NFS) to > handle their own error tracking and reporting without using the new > infrastructure. If they never call mapping_set_error then we'll always > just return whatever their ->fsync operation returns on an fsync. OK, makes sense. It is also in line with what you did for DAX, 9p, or here for FUSE. So feel free to add: Reviewed-by: Jan Kara <jack@xxxxxxx> for this patch but please also add a sentense that ->writepage() is responsible for calling mapping_set_error() if it fails and page is not redirtied to the changelogs of patches changing writepage handlers. > I'll make another pass through the tree and see whether we have some > mapping_set_error calls that should be removed, and will flesh out > vfs.txt to state this. Maybe that file needs a whole section on > writeback error reporting? Hmmm... I think it would be nice to have all the logic described in one place. So +1 from me. > That probably also means that I should drop patch 8 from this series > (mm: ensure that we set mapping error if writeout fails), since that > should be happening in writepage already. Yes. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
