On Mon, May 19, 2014 at 11:43:13AM +0200, Jan Kara wrote: > On Fri 16-05-14 10:11:56, Dave Chinner wrote: > > On Fri, May 16, 2014 at 01:19:09AM +0200, Mateusz Guzik wrote: > > > On Fri, May 16, 2014 at 08:51:41AM +1000, Dave Chinner wrote: > > > > On Fri, May 16, 2014 at 12:34:40AM +0200, Mateusz Guzik wrote: > > > > > On Fri, May 16, 2014 at 08:21:35AM +1000, Dave Chinner wrote: > > > > > > > IOW, a new column in mountinfo. For frozen filesystems it would contain > > > > > > > 'frozen_by=[%s]:[%d]' (escaped comm, pid). > > > > > > > > > > > > I really don't see that the process that froze the filesystem is > > > > > > particularly useful - it many cases that process is long gone (e.g. > > > > > > fsfreeze is being used to allow a HW array to take a snapshot). Just > > > > > > the fact it is in the process of freezing (if stuck, stack trace in > > > > > > sysrq-w should be present) or frozen (freezing process may be long > > > > > > gone, and is mostly irrelevant because you're now tracking down why > > > > > > a thaw hasn't happened)... > > > > > > > > > > There are deamons which perform freezing and unfreezing on their own. > > > > > Thus storing the name along with pid helps to determine whether someone > > > > > went behind such daemon's back, or maybe it's the daemon which "forgot" to > > > > > unfreeze after all. > > > > > > > > Such a daemon should be logging the fact that it's freezing and > > > > thawing the filesystem. The kernel is not the place to track what > > > > buggy userspace applications are doing wrong. > > > > > > > > > > Except there is no log entry if /var got frozen (and this is not an > > > imaginary example). > > > > Freezing the filesystem that the freezing daemon logs to is, well, a > > major application architecture fail. Sorry, catering for the lowest > > common denominator (i.e. stupidity) is not an valid argument for > > adding stuff to the kernel.... > Sure it's not a good architecture but it happens either because of a bug > or a wrong architecture. So you need to debug it and traces from sysrq-w > don't tell you who froze the filesystem. Currently you have to use > tracepoints or similar stuff to find that out (e.g. in one case I was > debugging it was rpm running a post-install script that froze the fs, > believe me that was really unexpected :)). But tracepoints aren't useful > after the fact so sometimes it would be useful to be able to find out > after the fact who froze the fs (PID and command name to help with > situations when the process isn't running anymore). Since this is mostly > debug stuff I'd be OK with dumping this information on sysrq request or as > Ted suggested from some fs-freeze hang check timer... Hmm? Sure, along with all the memory allocation, copying and freeing stuff that isn't guaranteed to be around if a hang occurs. And it has to be per-sb, because you can indepenently freeze multiple filesystems at the same time, and so on. I just don't see the complexity as being worthwhile given how rare freeze problems are... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
