linux-kernel - Re: [CFT] Re: VFS deadlock ?

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Message-ID: <20130322060953.GN21522@ZenIV.linux.org.uk>
Date:	Fri, 22 Mar 2013 06:09:53 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [CFT] Re: VFS deadlock ?

On Thu, Mar 21, 2013 at 10:33:27PM -0700, Linus Torvalds wrote:

> Ok, that's kind of ugly, but shouldn't be a correctness issue. It
> should still work - just cycle through inodes quite aggressivelydue to
> no longer re-using them - so I suspect Dave could test it (with the
> extra line removed I pointed out just a moment ago).
> 
> And I wonder how big of a deal the aggressive dentry deletion is.
> Maybe it's even ok to allocate/free the inodes all the time. The whole
> "get the inode hash lock and look it up there" can't be all that
> wonderful either. It takes the inode->i_lock for each entry it finds
> on the hash list, which looks horrible. I suspect our slab allocator
> isn't much worse than that, although the RCU freeing of the inodes
> could end up being problematic.

Hell knows...  At the very least, I'd expect /proc/self to be fairly hot.
During the boot time - /proc/mounts, /proc/filesystems, /proc/cmdline...
Dunno.  Would be interesting to slap a printk into proc_lookup_de() and
see how much (and what) does it hit on a busy system...
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