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Date: Thu, 12 Dec 2013 13:49:56 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: Potentially unbounded allocations in seq_read?
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On Thu, Dec 12, 2013 at 01:40:40PM +0000, Tvrtko Ursulin wrote:

> So this is the story... task_mmu.c:show_map_vma() calls seq_path. There
> we have a d_path call which returns -ENAMETOOLONG and keeps doing so
> even though the buffer grows to huge proportions. It is something on
> tmpfs, don't know what.
> 
> But in the meantime, shouldn't seq_path be a bit more considerate on
> this particular error and not mark the state as "could not fit" forever?
> Perhaps it would make sense to limit it a bit?
> 
> Or even more so, on errors _other_ than -ENAMETOOLONG it will at the
> moment mark the result as "need more space". That also sounds broken to
> me.

a) *what* errors other than -ENAMETOOLONG?
b) d_path() not fitting into 2Mb is definitely a bug.  If you really have
managed to get a dentry tree 1 million levels deep, you have much worse
problems.
c) which kernel version it is?