Re: [BUGS] [CHECKER] 99 synchronization bugs and a lock summary database

[Nathan Scott <nathans@sgi.com>]

On Thu, Jul 01, 2004 at 06:01:00PM -0700, Yichen Xie wrote:
> Hi all, 

Hi there,

> We are a group of researchers at Stanford working on program analysis
> algorithms.  We have been building a precision enhanced program analysis
> engine at Stanford, and our first application was to derive mutex/lock
> behavior in the linux kernel. In the process, we found 99 likely
> synchronization errors in linux kernel version 2.6.5:
> 
>     http://glide.stanford.edu/linux-lock/err1.html (69 errors)
>     http://glide.stanford.edu/linux-lock/err2.html (30 errors)
> 
>  ...
> 
> As always, feedbacks and confirmations will be greatly appreciated!

>From looking through the XFS reports, I suspect your tools aren't
following the sv_wait semantics correctly (or else I'm misreading
the code).  Many of the reported XFS items stem from this - e.g.
this one...
[NOTE] BUG forgot to unlock before "goto try_again" (line 2293)
ERROR: fs/xfs/xfs_log.c:2948: lock check failed!
ERROR: fs/xfs/xfs_log.c:xlog_state_sync

the code in question does this:

  try_again:
	s = LOG_LOCK(log); /* spin_lock(&log->l_icloglock); */
	    ...
		sv_wait(&iclog->ic_prev->ic_writesema, PSWP,
			&log->l_icloglock, s);
		already_slept = 1;
		goto try_again;

and the tools seem to be missing that the log->l_icloglock is
unlocked by the sv_wait routine.  Well, that or I've overlooked
something that the tools have not. :)

A couple of the others were definately missed unlocks on error
paths though (fixed now) - thanks!

cheers.

-- 
Nathan