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The subsequent > !pmd_present() branch has a VM_BUG_ON() asserting migration is the only > allowed non-present case; a device-private PMD trips it. > > Potential trigger: an HMM-based GPU driver races with > madvise(MADV_COLD)/MADV_PAGEOUT: pmd_trans_huge(*pmd) reads true, then > migrate_vma_pages() flips the PMD to a device-private entry before the > PMD lock is acquired. > > Skip device-private PMDs after taking the lock, before the !pmd_present() > check. > > Reported-by: sashiko-bot > Link: https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=6 > Fixes: 368076f52ebe ("mm/huge_memory: add device-private THP support to PMD operations") > Signed-off-by: Usama Arif > --- > mm/madvise.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/madvise.c b/mm/madvise.c > index 9292f60b19aa..870be398c6f3 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -384,6 +384,9 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, > return 0; > > orig_pmd = *pmd; > + if (pmd_is_device_private_entry(orig_pmd)) > + goto huge_unlock; > + > if (is_huge_zero_pmd(orig_pmd)) > goto huge_unlock; > > Reviewed-by: Balbir Singh