linux-kernel - Re: [fuse-devel] [PATCH] fuse: break infinite loop in fuse_fill_write

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Message-Id: <20151002150440.e691f6c81619794f8a947263@linux-foundation.org>
Date:	Fri, 2 Oct 2015 15:04:40 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Maxim Patlasov <mpatlasov@...allels.com>
Cc:	Konstantin Khlebnikov <koct9i@...il.com>,
	Roman Gushchin <klamm@...dex-team.ru>,
	<fuse-devel@...ts.sourceforge.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Miklos Szeredi <miklos@...redi.hu>
Subject: Re: [fuse-devel] [PATCH] fuse: break infinite loop in
 fuse_fill_write_pages()

On Fri, 2 Oct 2015 12:27:45 -0700 Maxim Patlasov <mpatlasov@...allels.com> wrote:

> On 10/02/2015 04:21 AM, Konstantin Khlebnikov wrote:
> > Bump. Add more peopple in CC.
> >
> > On Mon, Sep 21, 2015 at 1:02 PM, Roman Gushchin <klamm@...dex-team.ru> wrote:
> >> I got a report about unkillable task eating CPU. Thge further
> >> investigation shows, that the problem is in the fuse_fill_write_pages()
> >> function. If iov's first segment has zero length, we get an infinite
> >> loop, because we never reach iov_iter_advance() call.
> 
> iov_iter_copy_from_user_atomic() eventually calls iterate_iovec(). The 
> latter silently consumes zero-length iov. So I don't think "iov's first 
> segment has zero length" can cause infinite loop.

I'm suspecting it got stuck because local variable `bytes' is zero, so
the code does `goto again' repeatedly.

Or maybe not.   A more complete description of the bug would help. 
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