stalled 'sync' on ext3+quota over drbd

Stephen C. Tweedie sct at
Wed Mar 31 13:49:34 UTC 2004


On Wed, 2004-03-31 at 14:05, Eugene Crosser wrote:

> That'd be tricky: it is somewhere in the kernel (top shows 99% CPU used
> by "system", and strace attaced to sync does not show anything).

You'd need a kernel profile, not a user-space one, if it's all in system

> I'd be happy to provide more information but so far I cannot decide
> where to look...  Should I learn to use "kernel profiling"?

Sound like it.  You've got two choices --- the simple "readprofile"
(boot with profile=2), or set up an oprofile kernel.  For complex
user/kernel interactions oprofile can be really helpful, but for
something that's simply stuck in the kernel, readprofile is fine.

If the kernel is in a really tight loop, though, then simply using the
"altgr-scrlck" combination a few times is usually enough to find out
where it's looping.  That keystroke just dumps a stacktrace of whatever
CPU caught the keyboard interrupt, and if you're spinning in kernel
space, that backtrace will include the stack trace of whatever kernel
code is running in the foreground at the time.


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