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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id q5-20020acac005000000b0034fddfc5922sm1466958oif.36.2022.09.27.22.16.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Sep 2022 22:16:44 -0700 (PDT) Date: Tue, 27 Sep 2022 22:16:35 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Matthew Wilcox , Vlastimil Babka cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: amusing SLUB compaction bug when CC_OPTIMIZE_FOR_SIZE Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1664342205; a=rsa-sha256; cv=none; b=SaZ66VUX51ZghlezapSFKTHa/BCOOn3mpRFx6O3bX68FQOsVs2pgteBYricb1je9JRJx7u 9xeYQmmG7i1c9MbMiC/eaTfn1jbQr1ssMf4KHX4jcmL7YRCDNxt/MQ44FAwrzfT/PKfqRD 8Ic59jnnKGJmnKWuZRdXH3AdUXfYlvU= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=rp3aMO0g; spf=pass (imf16.hostedemail.com: domain of hughd@google.com designates 209.85.160.41 as permitted sender) smtp.mailfrom=hughd@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1664342205; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding:in-reply-to: references:dkim-signature; bh=RRxMxuisd8lNkNGWBlf9ZKEk1omHCIF/OzgSnFJx1kM=; b=tmi7nIPbr4ryQ1kR07Xt7EzN7WdxNpOXnL1AWtYTsmkd8A3RYKNNHWh5K42TpJ6sjzDq6q MzJHig/dNwyNYxRl56+HgE6CUWlsM+3NoX+8BLMlLsLbSph/NdaXluIWMSpb6DrIR7OvfC bmRbXMPbwEtHxB8mmu+F9cVBSASGG5M= X-Stat-Signature: 7dzpxb8kdmhbshc98a9eff9g4mbf1n8m X-Rspamd-Queue-Id: 8D36E180004 X-Rspam-User: Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=rp3aMO0g; spf=pass (imf16.hostedemail.com: domain of hughd@google.com designates 209.85.160.41 as permitted sender) smtp.mailfrom=hughd@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam08 X-HE-Tag: 1664342205-213948 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: It's a bug in linux-next, but taking me too long to identify which commit is "to blame", so let me throw it over to you without more delay: I think __PageMovable() now needs to check !PageSlab(). I had made a small experimental change somewhere, rebuilt and rebooted, was not surprised to crash once swapping and compaction came in, but was surprised to find the crash in isolate_movable_page(), called by compaction's isolate_migratepages_block(). page->mapping was ffffffff811303aa, which qualifies as __PageMovable(), which expects struct movable_operations at page->mapping minus low bits. But ffffffff811303aa was the address of SLUB's rcu_free_slab(): I have CONFIG_CC_OPTIMIZE_FOR_SIZE=y, so function addresses may have low bits set. Over to you! Thanks, Hugh