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Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5] mm/userfaultfd: detect VMA type change after copy retry in mfill_copy_folio_retry() Message-ID: References: <20260409120653.290386-1-devnexen@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: D732EC000E X-Stat-Signature: tbmfricetdbiruqdkbcqy4c96ha4xn5e X-Rspam-User: X-HE-Tag: 1775758355-852249 X-HE-Meta: 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 MPEl8sVf JXF+bdO2xmOTSTCxZ29H6A0bsjC1rzTpX7mOKrpBxjN3LkcfrsKi0SkwCxH0q03Jggh/M2wW3CTCB1KRxzOodG6dLAq72zEWrgxabuKh6TVW6xhDym+ZKQsUQwGTAPG7OLBxxxX68A/KPAV1uLWxG0ttMOp6Vrlp+RlReOWClSKb1k3Aco+tNSRPc7lBmkT0ho4H04XAQIGb/D7w0a2KSfbc/He/XbZe2L/a7Gc7D9OXUkZoY/d7DkcBLLXl6Gnzvs+29Qg0gG9dAPxh7CBU2VDdw+Ek4MCX3QJ2r92WeOVSMqeo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Apr 09, 2026 at 01:09:41PM -0400, Peter Xu wrote: > On Thu, Apr 09, 2026 at 01:06:53PM +0100, David Carlier wrote: > > @@ -465,6 +467,14 @@ static int mfill_copy_folio_retry(struct mfill_state *state, struct folio *folio > > if (err) > > return err; > > > > + /* > > + * The VMA type may have changed while the lock was dropped > > + * (e.g. replaced with a hugetlb mapping), making the caller's > > + * ops pointer stale. > > + */ > > + if (vma_uffd_ops(state->vma) != ops) > > + return -EAGAIN; > > I agree with -EAGAIN here, but we discussed over all the things on possible > inode change and I don't know why we don't consider that. > > I still think those should be considered. > > If the vma snapshot idea is not welcomed, fine. We need to think of > something to cover those too. Current patch won't cover "ops unchaged" but > "inode changed", or offset changed, for example. This patch is enough to fix the regression introduced by my refactoring. The inode/file/vma_snapshot checks are needed to solve the issue that existed roughly for a decade. This should be a separate patch and it's really not urgent. > Thanks, > -- > Peter Xu > -- Sincerely yours, Mike.