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X-Proofpoint-ORIG-GUID: 6B34uem0Gwbe_0LB3q8Z7KTU7-oYobzf On 3/10/2026 4:05 AM, Jianhui Zhou wrote: > In mfill_atomic_hugetlb(), linear_page_index() is used to calculate the > page index for hugetlb_fault_mutex_hash(). However, linear_page_index() > returns the index in PAGE_SIZE units, while hugetlb_fault_mutex_hash() > expects the index in huge page units. This mismatch means that different > addresses within the same huge page can produce different hash values, > leading to the use of different mutexes for the same huge page. This can > cause races between faulting threads, which can corrupt the reservation > map and trigger the BUG_ON in resv_map_release(). > > Fix this by introducing hugetlb_linear_page_index(), which returns the > page index in huge page granularity, and using it in place of > linear_page_index(). > > Fixes: a08c7193e4f1 ("mm/filemap: remove hugetlb special casing in filemap.c") > Reported-by: syzbot+f525fd79634858f478e7@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=f525fd79634858f478e7 > Cc: stable@vger.kernel.org > Signed-off-by: Jianhui Zhou > --- > v4: > - Introduce hugetlb_linear_page_index() instead of exposing > vma_hugecache_offset(); call hstate_vma() internally to simplify > the API (David Hildenbrand) > > v3: > - Fix Fixes tag to a08c7193e4f1 (Hugh Dickins) > > v2: > - Remove unnecessary !CONFIG_HUGETLB_PAGE stub for vma_hugecache_offset() > (Peter Xu, SeongJae Park) > > include/linux/hugetlb.h | 17 +++++++++++++++++ > mm/userfaultfd.c | 2 +- > 2 files changed, 18 insertions(+), 1 deletion(-) > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index 65910437be1c..67d4f0924646 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -796,6 +796,23 @@ static inline unsigned huge_page_shift(struct hstate *h) > return h->order + PAGE_SHIFT; > } > > +/** > + * hugetlb_linear_page_index() - linear_page_index() but in hugetlb > + * page size granularity. > + * @vma: the hugetlb VMA > + * @address: the virtual address within the VMA > + * > + * Return: the page offset within the mapping in huge page units. > + */ > +static inline pgoff_t hugetlb_linear_page_index(struct vm_area_struct *vma, > + unsigned long address) > +{ > + struct hstate *h = hstate_vma(vma); > + > + return ((address - vma->vm_start) >> huge_page_shift(h)) + > + (vma->vm_pgoff >> huge_page_order(h)); > +} > + > static inline bool order_is_gigantic(unsigned int order) > { > return order > MAX_PAGE_ORDER; > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 927086bb4a3c..5590989e18c7 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -573,7 +573,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb( > * in the case of shared pmds. fault mutex prevents > * races with other faulting threads. > */ > - idx = linear_page_index(dst_vma, dst_addr); > + idx = hugetlb_linear_page_index(dst_vma, dst_addr); Just wondering whether making the shift explicit here instead of introducing another hugetlb helper might be sufficient? idx >>= huge_page_order(hstate_vma(vma)); I mean huge_page_order() is already explicitly called in several places outside hugetlb. > mapping = dst_vma->vm_file->f_mapping; > hash = hugetlb_fault_mutex_hash(mapping, idx); > mutex_lock(&hugetlb_fault_mutex_table[hash]); thanks, -jane