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.... > Grabbig a debugger to inspect daemon's state is not > exactly what your typical support associate can or should do. No, but they can read /proc/self/mountinfo, and grab sysrq-w output. And they should be able to read that and tell that there is a freeze hang from that info. This "filesystem hang triage 101" stuff.... > But this was a side request, I'm not going to argue about including > this since turns out there is a better way. > > Somewhere in the thread an idea to log long-standing freezes was > mentioned which would provide sufficient information as far as You've already got the hung task timer firing when a fs is frozen for too long. You'll see processes hung in sb_write_wait(), and that tells you the filesystem is frozen. Then look at /proc/self/mountinfo to find which fs is frozen.... 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
