From: Paul Mackerras Date: Thu, 13 Nov 2014 09:15:23 +0000 (+1100) Subject: Fix thinko in iov_iter_single_seg_count X-Git-Tag: v3.17.4~67 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0c883ddfde0b06e27a2d3007cb1e8e0e188f92bd;p=thirdparty%2Fkernel%2Fstable.git Fix thinko in iov_iter_single_seg_count commit ad0eab9293485d1c06237e9249f6d4dfa3d93d4d upstream. The branches of the if (i->type & ITER_BVEC) statement in iov_iter_single_seg_count() are the wrong way around; if ITER_BVEC is clear then we use i->bvec, when we should be using i->iov. This fixes it. In my case, the symptom that this caused was that a KVM guest doing filesystem operations on a virtual disk would result in one of qemu's threads on the host going into an infinite loop in generic_perform_write(). The loop would hit the copied == 0 case and call iov_iter_single_seg_count() to reduce the number of bytes to try to process, but because of the error, iov_iter_single_seg_count() would just return i->count and the loop made no progress and continued forever. Signed-off-by: Paul Mackerras Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- diff --git a/mm/iov_iter.c b/mm/iov_iter.c index 9a09f2034fcc5..141dcf796d280 100644 --- a/mm/iov_iter.c +++ b/mm/iov_iter.c @@ -699,9 +699,9 @@ size_t iov_iter_single_seg_count(const struct iov_iter *i) if (i->nr_segs == 1) return i->count; else if (i->type & ITER_BVEC) - return min(i->count, i->iov->iov_len - i->iov_offset); - else return min(i->count, i->bvec->bv_len - i->iov_offset); + else + return min(i->count, i->iov->iov_len - i->iov_offset); } EXPORT_SYMBOL(iov_iter_single_seg_count);