Re: [PATCH] fix unbalanced page refcounting in bio_map_user_iov

From	Al Viro <viro@ZenIV.linux.org.uk>
Newsgroups	linux.kernel
Subject	Re: [PATCH] fix unbalanced page refcounting in bio_map_user_iov
Date	2017-09-24 19:20 +0200
Message-ID	<utiJr-32Y-5@gated-at.bofh.it> (permalink)
References	(1 earlier) <usVDb-5pJ-23@gated-at.bofh.it> <usVWy-5ym-7@gated-at.bofh.it> <usWfU-5U4-11@gated-at.bofh.it> <usZns-7Qw-5@gated-at.bofh.it> <utg4W-1lc-17@gated-at.bofh.it>
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On Sun, Sep 24, 2017 at 03:27:39PM +0100, Al Viro wrote:

> At the very least, we need bmd->iter = *iter; bmd->iter.iov = bmd->iov;
> instead of that iov_iter_init() in there.  I'm not sure how far back does
> it go; looks like "block: support large requests in blk_rq_map_user_iov"
> is the earliest possible point, but it might need more digging to make
> sure.  v4.5+, if that's when the problems began...
> 
> Anyway, I'd added the obvious fix to #work.iov_iter, reordered it and
> force-pushed the result.

While we are at it, calculation of nr_pages in bio_copy_user_iov() is bloody
odd - why, in the name of everything unholy, does it care about the iovec
boundaries in there?  We are copying data anyway; why does allocation of bio
care about the fragmentation of the other end of copying?  Shouldn't it be
simply max(DIV_ROUND_UP(offset + len, PAGE_SIZE), BIO_MAX_PAGES)?

Thread

[PATCH] fix unbalanced page refcounting in bio_map_user_iov Vitaly Mayatskikh <v.mayatskih@gmail.com> - 2017-09-22 07:20 +0200
  Re: [PATCH] fix unbalanced page refcounting in bio_map_user_iov Vitaly Mayatskikh <v.mayatskih@gmail.com> - 2017-09-22 07:30 +0200
  Re: [PATCH] fix unbalanced page refcounting in bio_map_user_iov Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-23 18:40 +0200
    Re: [PATCH] fix unbalanced page refcounting in bio_map_user_iov Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-23 19:00 +0200
      Re: [PATCH] fix unbalanced page refcounting in bio_map_user_iov Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-23 19:20 +0200
        Re: [PATCH] fix unbalanced page refcounting in bio_map_user_iov Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-23 22:40 +0200
          Re: [PATCH] fix unbalanced page refcounting in bio_map_user_iov Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-24 16:30 +0200
            Re: [PATCH] fix unbalanced page refcounting in bio_map_user_iov Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-24 19:20 +0200
            Re: [PATCH] fix unbalanced page refcounting in bio_map_user_iov Vitaly Mayatskikh <v.mayatskih@gmail.com> - 2017-09-25 03:50 +0200

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