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[198.145.29.99]) by mx.google.com with ESMTPS id c11si13127281pjq.0.2019.07.23.11.19.05 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 23 Jul 2019 11:19:05 -0700 (PDT) Received-SPF: pass (google.com: domain of jlayton@kernel.org designates 198.145.29.99 as permitted sender) client-ip=198.145.29.99; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=pAq+kDaH; spf=pass (google.com: domain of jlayton@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=jlayton@kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: from tleilax.poochiereds.net (cpe-71-70-156-158.nc.res.rr.com [71.70.156.158]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 624C62084D; Tue, 23 Jul 2019 18:19:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563905945; bh=Awat9gsewjbgPYbV/sg1258A8MvYYSlvsfznyoqnKc8=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=pAq+kDaHErUf7z0A9YeuslsNjOOpqTeBmy2yWZ/WPZnlJXKuWhoBj4PA0sRvyshLP rBChVn4/w7vvs9e33FUkKT96KV42rbexeF9eW4c084faYM+yuugLVh0sxDslZE8WMd CiJwB7vdVBFo4aBCYavOSAWt1sD0ejfSPloUQMLU= Message-ID: Subject: Re: [PATCH] mm: check for sleepable context in kvfree From: Jeff Layton To: Matthew Wilcox Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, lhenriques@suse.com, cmaiolino@redhat.com, Christoph Hellwig Date: Tue, 23 Jul 2019 14:19:03 -0400 In-Reply-To: <20190723181124.GM363@bombadil.infradead.org> References: <20190723131212.445-1-jlayton@kernel.org> <3622a5fe9f13ddfd15b262dbeda700a26c395c2a.camel@kernel.org> <20190723175543.GL363@bombadil.infradead.org> <20190723181124.GM363@bombadil.infradead.org> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.32.4 (3.32.4-1.fc30) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit 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, 2019-07-23 at 11:11 -0700, Matthew Wilcox wrote: > On Tue, Jul 23, 2019 at 02:05:11PM -0400, Jeff Layton wrote: > > On Tue, 2019-07-23 at 10:55 -0700, Matthew Wilcox wrote: > > > > HCH points out that xfs uses kvfree as a generic "free this no matter > > > > what it is" sort of wrapper and expects the callers to work out whether > > > > they might be freeing a vmalloc'ed address. If that sort of usage turns > > > > out to be prevalent, then we may need another approach to clean this up. > > > > > > I think it's a bit of a landmine, to be honest. How about we have kvfree() > > > call vfree_atomic() instead? > > > > Not a bad idea, though it means more overhead for the vfree case. > > > > Since we're spitballing here...could we have kvfree figure out whether > > it's running in a context where it would need to queue it instead and > > only do it in that case? > > > > We currently have to figure that out for the might_sleep_if anyway. We > > could just have it DTRT instead of printk'ing and dumping the stack in > > that case. > > I don't think we have a generic way to determine if we're currently > holding a spinlock. ie this can fail: > > spin_lock(&my_lock); > kvfree(p); > spin_unlock(&my_lock); > > If we're preemptible, we can check the preempt count, but !CONFIG_PREEMPT > doesn't record the number of spinlocks currently taken. Ahh right...that makes sense. Al also suggested on IRC that we could add a kvfree_atomic if that were useful. That might be good for new callers, but we'd probably need a patch like this one to suss out which of the existing kvfree callers would need to switch to using it. I think you're quite right that this is a landmine. That said, this seems like something we ought to try to clean up. -- Jeff Layton