Re: 2.6.17-rc5-mm2

[Arjan van de Ven <arjan@linux.intel.com>]

> > http://www.stardust.webpages.pl/files/mm/2.6.17-rc5-mm2/bug_2.jpg
> 
> So it's claiming that we're taking multiple i_mutexes.
> 
> I can't immediately see where we took the outermost i_mutex there.

inlining caused one level to be removed from the backtrace
one level is in fs_remove_file, the sub level is usbfs_unlink (called
from fs_remove_file)

>   Nor is
> it immediately obvious why this is considered to be deadlockable?

what is missing is that we tell lockdep that there is a parent-child
relationship between those two i_mutexes, so that it knows that 1)
they're separate and 2) that the lock take order is parent->child


> (lockdep tells us that a mutex was taken at "mutex_lock+0x8/0xa", which is
> fairly useless.  We need to report who the caller of mutex_lock() was).

yeah this has been bugging me as well; either via a wrapper around
mutex_lock or via the gcc option to backwalk the stack (but that only
works with frame pointers enabled.. sigh)
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