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[209.85.208.48]) by smtp.gmail.com with ESMTPSA id a23-20020a1709065f9700b0098f99048053sm8529626eju.148.2023.07.25.09.38.50 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Jul 2023 09:38:50 -0700 (PDT) Received: by mail-ed1-f48.google.com with SMTP id 4fb4d7f45d1cf-5222c5d71b8so3387984a12.2 for ; Tue, 25 Jul 2023 09:38:50 -0700 (PDT) X-Received: by 2002:aa7:d707:0:b0:522:3149:1596 with SMTP id t7-20020aa7d707000000b0052231491596mr5134940edq.13.1690303129829; Tue, 25 Jul 2023 09:38:49 -0700 (PDT) MIME-Version: 1.0 References: <8d063a26-43f5-0bb7-3203-c6a04dc159f8@proxmox.com> In-Reply-To: <8d063a26-43f5-0bb7-3203-c6a04dc159f8@proxmox.com> From: Linus Torvalds Date: Tue, 25 Jul 2023 09:38:32 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: segfaults of processes while being killed after commit "mm: make the page fault mmap locking killable" To: Fiona Ebner , "Eric W. Biederman" , Oleg Nesterov Cc: akpm@linux-foundation.org, Thomas Lamprecht , Wolfgang Bumiller , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: multipart/mixed; boundary="0000000000009e069c0601525dd0" X-Rspamd-Queue-Id: 48D7412000E X-Rspam-User: X-Stat-Signature: xg4ee1nukjth5e61zad1mjxjx4bdocjp X-Rspamd-Server: rspam01 X-HE-Tag: 1690303133-982314 X-HE-Meta: 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 YULn7lvl MgEQjY6ii6CrfNYPSaje14YVffijAw4nd7C5lQhaea/Ak9rAzIUtn6tND0+S6ytBi5v0ZRTszQESRfd9vwfsOlPrqhxKK57Hzc6jL4zqZSFnJgbabm6olE4OJbFJlk/dotnjqIybnmSOjif8vr8MGAK4wAksdaQjhbc2g6jZS6CF5bnL565eaBvRB8ODj2y+AmxnNdQMC7MXOB6FijTTWfjkS+dj62N/6mqT0XOave2WOH+HoC8h0g08LEjn5y7V47zRgILaIeiAnPajpJRE3H2Eyzm8tplOiHZeSm9Le2KiFb3GpVe7PTgIRkDSkn89FiOH3enPoMXKoDixo1bbE2ahFp6bao7guttaypPvLaoE/lnato6k07ZJc89knMiDgc84t1IBedsW0/3dSYIh0kHWo4tq1gZtP8EWOjP550spJmLxGUGfQ4bEtMZtU9RF0AWie/tTOaT9fQo4spNtpCA6aVJka+pRW+ypHqtsjc6RwyvA0IDR9l/hPVlFC4psJFiN7M7DdhWjO30gzZ4W9ZmGTX862taMD7TS/GHU9m1gX/vfklEeOmplrKVaOIscw1cBKhENcKad4Zh0pZnlTogtcJ/o7kPRnfdV2APVOAHaSpKOHGkIvphJLZVkxRLSMPz6nIgfSYschc5GZxMGBgmGmWw6lHAyvygr0YjeLnc4XAQ5Gapux8RcxQ09HT1i3uhpZYvEfEKCRbVl/jEDzx7TSiPWwBwOHtGUxNn0JbTiWzIuldo8zEeyROI/aUN2/Nlr9B/yEXDfo1YAhvn8T1hIqjw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: --0000000000009e069c0601525dd0 Content-Type: text/plain; charset="UTF-8" On Tue, 25 Jul 2023 at 04:16, Fiona Ebner wrote: > > will end up without a vma and cause/log the segfault. Of course the > process is already being killed, but I'd argue it is very confusing to > users when apparent segfaults from such processes are being logged by > the kernel. Ahh. Yes, that wasn't the intent. A process that is being killed should exit with the lethal signal, not SIGSEGV. This is not new, btw - this situation is exactly the same as if you use something like NFS where the process is killed and the IO is interrupted and the page fault faults for that reason. But I suspect *very* few people actually encounter that NFS situation (you can get it on local filesystems too, but the IO race window is then so small as to probably not be triggerable at all). So the new killable() check is probably much easier to actually trigger in practice, even though it's not a new situation per se. What exactly made you notice? Is it just the logging from 'show_unhandled_signals' being set? Because the actual signal itself, from the force_sig_fault(SIGSEGV, si_code, (void __user *)address); in __bad_area_nosemaphore() should be overridden by the fact that a lethal signal was already pending. But let's add a couple of signal people rather than the mm people to the participants. Eric, Oleg - would not an existing fatal signal take precedence over a new SIGSEGV? I obviously thought it did, but looking at 'get_signal()' and the signal delivery, I don't actually see any code to that effect. Fiona - that patch is easily reverted, and it was done as a separate patch exactly because I was wondering if there was some subtle reason we didn't already do that. But before we revert it, would you mind trying out the attached trivial patch instead? I'd also still be interested if the symptoms were anything else than 'show_unhandled_signals' causing the show_signal_msg() dance, and resulting in a message something like a.out[1567]: segfault at xyz ip [..] likely on CPU X in dmesg... Linus --0000000000009e069c0601525dd0 Content-Type: text/x-patch; charset="US-ASCII"; name="patch.diff" Content-Disposition: attachment; filename="patch.diff" Content-Transfer-Encoding: base64 Content-ID: X-Attachment-Id: f_lkiims3u0 IGFyY2gveDg2L21tL2ZhdWx0LmMgfCA0ICsrKysKIDEgZmlsZSBjaGFuZ2VkLCA0IGluc2VydGlv bnMoKykKCmRpZmYgLS1naXQgYS9hcmNoL3g4Ni9tbS9mYXVsdC5jIGIvYXJjaC94ODYvbW0vZmF1 bHQuYwppbmRleCBlODcxMWIyY2FmYWYuLmI0YTAyOTBlOTYzYyAxMDA2NDQKLS0tIGEvYXJjaC94 ODYvbW0vZmF1bHQuYworKysgYi9hcmNoL3g4Ni9tbS9mYXVsdC5jCkBAIC04MzEsNiArODMxLDEw IEBAIF9fYmFkX2FyZWFfbm9zZW1hcGhvcmUoc3RydWN0IHB0X3JlZ3MgKnJlZ3MsIHVuc2lnbmVk IGxvbmcgZXJyb3JfY29kZSwKIAkgKi8KIAlsb2NhbF9pcnFfZW5hYmxlKCk7CiAKKwkvKiBJZiBh IGZhdGFsIHNpZ25hbCBpcyBwZW5kaW5nLCBkb24ndCBib3RoZXIgd2l0aCBhbnl0aGluZyBlbHNl ICovCisJaWYgKGZhdGFsX3NpZ25hbF9wZW5kaW5nKCkpCisJCXJldHVybjsKKwogCS8qCiAJICog VmFsaWQgdG8gZG8gYW5vdGhlciBwYWdlIGZhdWx0IGhlcmUgYmVjYXVzZSB0aGlzIG9uZSBjYW1l CiAJICogZnJvbSB1c2VyIHNwYWNlOgo= --0000000000009e069c0601525dd0--