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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat, 13 Nov 2021 12:23:30 -0800
Message-ID: <CAHk-=wh2fa20a-qe+8q8no3_2MD-DokXvKNDhDC6qMJyCTvnPw@mail.gmail.com>
Subject: Re: [PATCH] mm: shmem: do not call PageHWPoison on a ERR-page
To:     Jens Axboe <axboe@kernel.dk>, Arnd Bergmann <arnd@arndb.de>,
        Yang Shi <shy828301@gmail.com>
Cc:     Ajay Garg <ajaygargnsit@gmail.com>,
        Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Sat, Nov 13, 2021 at 12:16 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Neither of the fixes were sent to me, and honestly, I think the real
> issue is that the original commit is just too broken for words.

Side note: the one you pointed to (by Ajay), had the comment that it
could be done differently as an optimization.

And I very much agree with that, although I think it would be a lot
more than an optimization: just doing

        if (error)
                return ERR_PTR(error);

earlier in the function would have avoided the issue entirely, and
would have made the code a lot easier to read too.

But what made me decide to just revert it entirely was that the
original commit that caused this all also had stuff like this:

-       return shmem_getpage(inode, index, pagep, SGP_WRITE);
+       ret = shmem_getpage(inode, index, pagep, SGP_WRITE);
+
+       if (*pagep && PageHWPoison(*pagep)) {
+               unlock_page(*pagep);
+               put_page(*pagep);
+               ret = -EIO;
+       }
+
+       return ret;

which is another example of exactly the same issue: ignoring errors,
and then acting on other information and creating new errors.

Again, that code should have checked and handled errors first, and
then - if there wasn't an error - added that new HWpoison handling.

So that just made me go "this is not worth fixing up, this just needs
re-doing", and thus I just went for the revert instead.

                   Linus