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Wed, 12 Aug 2026 10:59:44 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id sX6nGyBSfGr+UgAAD6G6ig (envelope-from ); Wed, 12 Aug 2026 10:59:44 +0000 Date: Wed, 12 Aug 2026 11:59:42 +0100 From: Pedro Falcato 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 , 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 3/3] mm: fail the fault on a malformed swap entry instead of retrying it Message-ID: References: <20260810-swap-v1-0-375ef0767206@debian.org> <20260810-swap-v1-3-375ef0767206@debian.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260810-swap-v1-3-375ef0767206@debian.org> X-Rspamd-Action: no action X-Rspam-User: X-Stat-Signature: anxpxo9jfioyx9izsgrrmzsqo6ok6oct X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: B0C6A40005 X-HE-Tag: 1786532395-161695 X-HE-Meta: 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 lSPQzjIo 8TWvDEvIMQxEisB37huejPvpGBeC8C6w0zO52yrPk+haJjN8FevShTgHmAKsZLNoLwRuNiwaefo6m7R1ub2P6I64drutYhYh1eqhSxQLcccJJTZ9JtjN0UXjtNzc10RBp/x4bx6j9EJvu94Tu5bT02S4cO7ZFEppQ37mWlGhx3dK7eneOFEQp8PlGMIcU/wuiDbpWaXUZWmhdLuIg30UlvKR02ljQphy6gE469EnTSF4MzTLb2UJ0xBVCEXw5Ehl2AWbd3nFmFtCgM67fE9X0ZO7iiw2M58RvPZ2PzkkTQOz2ZNYHE4CcA6F+K5ojLWHDcFCkRFRqFcdXVQ0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Aug 10, 2026 at 09:26:51AM -0700, 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 until it is > killed. > > Return VM_FAULT_SIGBUS for a malformed entry, as the sibling arm > already does for an unrecognised non-swap entry. A NULL return still > means swapoff, which is still worth retrying. What kind of SIGBUS do you get from this? as in the si_code. Out of all the options #define BUS_ADRALN 1 /* invalid address alignment */ #define BUS_ADRERR 2 /* non-existent physical address */ #define BUS_OBJERR 3 /* object specific hardware error */ /* hardware memory error consumed on a machine check: action required */ #define BUS_MCEERR_AR 4 /* hardware memory error detected in process but not consumed: action optional*/ #define BUS_MCEERR_AO 5 I would say this would fit none of them. The default (AFAICT) would be BUS_ADRERR, and I think that one is quite overloaded with meaning (namely, with regards to memory-mapped IO past EOF, or EIO on file IO). I wouldn't love to also use it for this, IMO. > > 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 4238778b66c42..2842cd976f1d3 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. */ > 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 > -- Pedro