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McKenney" , Zhang Qiang1 , "Uladzislau Rezki (Sony)" Subject: Re: [PATCH] mm/vmalloc: allow mem_dump_obj() to be called in interrupt context Message-Id: <20221114165443.98042d9244ee8899901df164@linux-foundation.org> In-Reply-To: <20221112121537.1634-1-thunder.leizhen@huawei.com> References: <20221112121537.1634-1-thunder.leizhen@huawei.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=pqdhGMeP; spf=pass (imf29.hostedemail.com: domain of akpm@linux-foundation.org designates 145.40.73.55 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1668473691; a=rsa-sha256; cv=none; b=q51iA8Ke5MJEQgAo2GNcvAy6+iMubM6ZwoTMnUVAEXNZWNc0/rZnUQkTqjHEmr2NkCWRaL Nvm35oiat5zQErXaf/WByT0kBoqh1O0VRMXjIo5lETje2GsuOkFrEeXWPA31+uXzqCrUpU E4XMcGaIQOtUHflcRxpcZul5Wr8qLgM= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1668473691; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=p1f5WV9SblnGH1VM+DVPQm7fe9qIdr4jjrPEeGebKHg=; b=5OkLckV1PVETjk78linRagTBSeJCZqpl86wkj+Rc3FVCACtFXSSN9rOGRFbwxboooVmqjF 6uipR10wTUlGRjRpn4y+UTaDrBZcGC/HiJgZ7wtRYw+dHpNgrsQNmeFc2HKgtcgPLU4MSg YY0uNU+Q8c515N475wDehwbfx5WFHBw= X-Stat-Signature: 6x36oixmc8ni6ub3u1pfsew64gdp6byw X-Rspamd-Queue-Id: EE23A120009 X-Rspam-User: Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=pqdhGMeP; spf=pass (imf29.hostedemail.com: domain of akpm@linux-foundation.org designates 145.40.73.55 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none X-Rspamd-Server: rspam11 X-HE-Tag: 1668473690-498642 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 Sat, 12 Nov 2022 20:15:37 +0800 Zhen Lei wrote: > The function mem_dump_obj() can sometimes provide valuable debugging > information, but it cannot be called in an interrupt context because > spinlock vmap_area_lock has not been protected against IRQs. If the > current task has held the lock before hard/soft interrupt handler calls > mem_dump_obj(), simply abandoning the dump operation can avoid deadlock. > That is, no deadlock occurs in extreme cases, and dump succeeds in most > cases. > > ... > > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -4034,6 +4034,9 @@ bool vmalloc_dump_obj(void *object) > struct vm_struct *vm; > void *objp = (void *)PAGE_ALIGN((unsigned long)object); > > + if (unlikely(spin_is_locked(&vmap_area_lock))) > + return false; > + > vm = find_vm_area(objp); > if (!vm) > return false; Yes, but this will worsen the current uses of this function. Consider the case where task A wants to call vmalloc_dump_obj() but task B holds vmap_area_lock. No problem, task A will simply spin until task B is done. But after this patch, task A's call to vmalloc_dump_obj() will return without having done anything.