linux-kernel - Re: [PATCH] Fix a race in pid generation that causes pids to be reused immediately.

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Date:	Mon, 14 Jun 2010 20:56:19 -0400
From:	tytso@....edu
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Salman <sqazi@...gle.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	tytso@...gle.com, torvalds@...ux-foundation.org, walken@...gle.com,
	Chen Liqin <liqin.chen@...plusct.com>,
	Lennox Wu <lennox.wu@...il.com>
Subject: Re: [PATCH] Fix a race in pid generation that causes pids to be
 reused immediately.

On Mon, Jun 14, 2010 at 04:58:51PM -0700, Andrew Morton wrote:
> Using
> 
> 	grep -r '[ 	]cmpxchg[^_]' . | grep -v /arch/
> 
> I can't see any cmpxchg() callers in truly generic code.  lockdep and
> kernel/trace/ring_buffer.c aren't used on the more remote
> architectures, I think.

What about:

drivers/gpu/drm/drm_lock.c:             prev = cmpxchg(lock, old, new);
kernel/lockdep.c:               n = cmpxchg(&nr_chain_hlocks, cn, cn + chain->de
kernel/sched_clock.c:   if (cmpxchg64(&scd->clock, old_clock, clock) != old_cloc
fs/btrfs/inode.c:       if (cmpxchg(&root->orphan_cleanup_state, 0, ORPHAN_CLEAN
fs/ext4/inode.c:        } while (cmpxchg(&ei->i_flags, old_fl, new_fl) != old_fl

The last is quite new --- I had just recently done a similar set of
research as you did before accepting the patch that added cmpxchg into
ext4 (during the last merge window), and I thought cmpxchg() had
entered the "supported by all architectures" category.  It looked like
it had only recently reached state, but I had reached the conclusion
that it was safe to use.

						- Ted
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