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 BFmYs/ES 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Oct 23, 2025 at 02:59:13PM +0800, Kairui Song wrote: > From: Kairui Song > > The order check and fallback loop is updating the index value on every > loop, this will cause the index to be wrongly aligned by a larger value > while the loop shrinks the order. > > This may result in inserting and returning a folio of the wrong index > and cause data corruption with some userspace workloads [1]. > > Cc: stable@vger.kernel.org > Link: https://lore.kernel.org/linux-mm/CAMgjq7DqgAmj25nDUwwu1U2cSGSn8n4-Hqpgottedy0S6YYeUw@mail.gmail.com/ [1] > Fixes: e7a2ab7b3bb5d ("mm: shmem: add mTHP support for anonymous shmem") > Signed-off-by: Kairui Song Yikes... LGTM so: Reviewed-by: Lorenzo Stoakes See below for a small nit. > > --- > > Changes from V2: > - Introduce a temporary variable to improve code, > no behavior change, generated code is identical. > - Link to V2: https://lore.kernel.org/linux-mm/20251022105719.18321-1-ryncsn@gmail.com/ > > Changes from V1: > - Remove unnecessary cleanup and simplify the commit message. > - Link to V1: https://lore.kernel.org/linux-mm/20251021190436.81682-1-ryncsn@gmail.com/ > > --- > mm/shmem.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/mm/shmem.c b/mm/shmem.c > index b50ce7dbc84a..e1dc2d8e939c 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1882,6 +1882,7 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf, > struct shmem_inode_info *info = SHMEM_I(inode); > unsigned long suitable_orders = 0; > struct folio *folio = NULL; > + pgoff_t aligned_index; Nit, but can't we just declare this in the loop? That makes it even clearer that we don't reuse the value. > long pages; > int error, order; > > @@ -1895,10 +1896,12 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf, > order = highest_order(suitable_orders); > while (suitable_orders) { > pages = 1UL << order; > - index = round_down(index, pages); > - folio = shmem_alloc_folio(gfp, order, info, index); > - if (folio) > + aligned_index = round_down(index, pages); > + folio = shmem_alloc_folio(gfp, order, info, aligned_index); > + if (folio) { > + index = aligned_index; > goto allocated; > + } > > if (pages == HPAGE_PMD_NR) > count_vm_event(THP_FILE_FALLBACK); > -- > 2.51.0 >