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Tue, 30 Aug 2022 06:46:58 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id Rhg4MmKyDWOXJQAAMHmgww (envelope-from ); Tue, 30 Aug 2022 06:46:58 +0000 Date: Tue, 30 Aug 2022 08:46:58 +0200 From: Michal Hocko To: Dan Carpenter Cc: linux-mm@kvack.org Subject: Re: [bug report] mm: reduce noise in show_mem for lowmem allocations Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1661842020; a=rsa-sha256; cv=none; b=HMWH51zskf2DyGAfh894iOfI2kNqiiFTpMONuMI+VHTZqMKeeVYwUvTewy1+fdHaLHyUZO sLJEtkcB2qhYpExlau70ds853n9LxL92LYs77WItkO9nzUA5VM8JWVmuUcwHbHy+B8um8E q2CNi2FN6bWcfyH07iaCGsBomhrYtuU= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=jeGD8urX; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf28.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1661842020; 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:in-reply-to:references:references:dkim-signature; bh=KnOXUg9g7Gw068LbehKMKX7IJPER/U3cPK95wkYImbg=; b=0J0dO+Oj5kAMHidEfmK7TRsbymkZK30ru1prIpKW+Cf+PqRnLZdW5O3gtZLkMfXk5lhYh/ /6sj05G7Nnn98m2B0NwKgKiZMTViPglNhFS/WBIxUTHyslcDBFpU/+yKGWSsJXkCFAPEpq Dj8Pm3MS63JZYqhJ6hawRDv5hNcK42I= X-Rspam-User: X-Rspamd-Queue-Id: 20FFCC0026 X-Rspamd-Server: rspam03 X-Stat-Signature: ysn85bdd4nid5uyru5m1bx1rko86j46o Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=jeGD8urX; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf28.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com X-HE-Tag: 1661842019-837083 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: On Tue 30-08-22 09:30:26, Dan Carpenter wrote: > Hello Michal Hocko, > > The patch e8fedfea3dea: "mm: reduce noise in show_mem for lowmem > allocations" from Aug 23, 2022, leads to the following Smatch static > checker warning: > > kernel/panic.c:190 panic_print_sys_info() > warn: sleeping in atomic context What is this warning saying? > kernel/panic.c > 175 static void panic_print_sys_info(bool console_flush) > 176 { > 177 if (console_flush) { > 178 if (panic_print & PANIC_PRINT_ALL_PRINTK_MSG) > 179 console_flush_on_panic(CONSOLE_REPLAY_ALL); > 180 return; > 181 } > 182 > 183 if (panic_print & PANIC_PRINT_ALL_CPU_BT) > 184 trigger_all_cpu_backtrace(); > 185 > 186 if (panic_print & PANIC_PRINT_TASK_INFO) > 187 show_state(); > 188 > 189 if (panic_print & PANIC_PRINT_MEM_INFO) > --> 190 show_mem(0, NULL, GFP_HIGHUSER_MOVABLE); > ^^^^^^^^^^^^^^^^^^^^ > This obviously seems very deliberate and a lot of weird stuff happens > during panic(). But the panic() function disables preemption so > shouldn't this be GFP_ATOMIC? GFP_HIGHUSER_MOVABLE has __GFP_RECLAIM > and triggering swap during a panic seems bad. This function shouldn't ever be allocating any memory. The flag is solely to infer which memory zones should be displayed. It acts as a filter. Is it possible that the checker misinterprets the parameter's meaning? -- Michal Hocko SUSE Labs