linux-kernel - Re: [PATCH] Initialise mmu_notifier

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Message-ID: <20190103144313.GR6310@bombadil.infradead.org>
Date:   Thu, 3 Jan 2019 06:43:13 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Jerome Glisse <jglisse@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christian König <christian.koenig@....com>,
        Jan Kara <jack@...e.cz>
Subject: Re: [PATCH] Initialise mmu_notifier_range correctly

On Thu, Jan 03, 2019 at 09:31:16AM -0500, Jerome Glisse wrote:
> On Wed, Jan 02, 2019 at 04:21:26PM -0800, Matthew Wilcox wrote:
> > 
> > One of the paths in follow_pte_pmd() initialised the mmu_notifier_range
> > incorrectly.
> > 
> > Signed-off-by: Matthew Wilcox <willy@...radead.org>
> > Fixes: ac46d4f3c432 ("mm/mmu_notifier: use structure for invalidate_range_start/end calls v2")
> > Tested-by: Dave Chinner <dchinner@...hat.com>
> 
> Actually now that i have read the code again this is not ok to
> do so. The caller of follow_pte_pmd() will call range_init and
> follow pmd will only update the range address. So existing code
> is ok.

I think you need to re-read your own patch.

`git show ac46d4f3c43241ffa23d5bf36153a0830c0e02cc`

@@ -4058,10 +4059,10 @@ static int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,
                if (!pmdpp)
                        goto out;
 
-               if (start && end) {
-                       *start = address & PMD_MASK;
-                       *end = *start + PMD_SIZE;
-                       mmu_notifier_invalidate_range_start(mm, *start, *end);
+               if (range) {
+                       mmu_notifier_range_init(range, mm, address & PMD_MASK,
+                                            (address & PMD_MASK) + PMD_SIZE);
+                       mmu_notifier_invalidate_range_start(range);

... so it's fine to call range_init() *here*.

@@ -4069,17 +4070,17 @@ static int __follow_pte_pmd(struct mm_struct *mm, unsign
ed long address,
[...]
        if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
                goto out;
 
-       if (start && end) {
-               *start = address & PAGE_MASK;
-               *end = *start + PAGE_SIZE;
-               mmu_notifier_invalidate_range_start(mm, *start, *end);
+       if (range) {
+               range->start = address & PAGE_MASK;
+               range->end = range->start + PAGE_SIZE;
+               mmu_notifier_invalidate_range_start(range);

... but then *not* here later in the same function?  You're not making
any sense.