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Tue, 18 Aug 2026 02:30:32 -0700 (PDT) Date: Tue, 18 Aug 2026 17:30:24 +0800 From: Kairui Song To: Breno Leitao Cc: Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , Hugh Dickins , Baolin Wang , Peter Xu , Johannes Weiner , Yosry Ahmed , Chengming Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v2 3/3] mm: fail the fault on a malformed swap entry instead of retrying it Message-ID: References: <20260813-swap-v2-0-4a625ccabdae@debian.org> <20260813-swap-v2-3-4a625ccabdae@debian.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260813-swap-v2-3-4a625ccabdae@debian.org> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 414D01C0009 X-Stat-Signature: n5jacnf7aggqud9ajcxrc4tusquijmjs X-Rspam-User: X-HE-Tag: 1787045434-699772 X-HE-Meta: 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 SEeFWSPR 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 13, 2026 at 03:02:22AM +0800, Breno Leitao wrote: > do_swap_page() returns 0 when get_swap_device() fails, which the fault > handler reads as "handled". For an entry that can never become valid > the retry takes the same fault again, so the thread spins forever, > retrying on the same fault. > > Return VM_FAULT_SIGBUS (Bad access) for a malformed entry (pr_err() was > called at get_swap_device()). > > Signed-off-by: Breno Leitao > --- > mm/memory.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/memory.c b/mm/memory.c > index 7201e848129a7..fa2b3d2ad3202 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4957,6 +4957,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > /* Prevent swapoff from happening to us, and reject a bad entry. */ > si = get_swap_device(entry); > if (IS_ERR_OR_NULL(si)) { > + /* A malformed entry never becomes valid, so don't retry it. */ > + if (IS_ERR(si)) > + ret = VM_FAULT_SIGBUS; > si = NULL; > goto out; > } > > -- > 2.53.0-Meta > Looks good to me but interesting b4 shazam will apply a Fixed tag to this, maybe it picked up the "Fixes" in discussion. I checked the discussion and the history behind this, 2799e77529c2 caused the loop, and 23b230ba8ac3 caused the pr_err spam. But before 2799e77529c2 it wasn't correct either, it was OOM kill. So anyway, the fix is good, we might omit the fixes tag on this I think, the behavior was never correct. Acked-by: Kairui Song