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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260813-swap-v2-3-4a625ccabdae@debian.org> 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