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[198.145.29.99]) by mx.google.com with ESMTPS id d22si11264900plr.120.2019.07.23.11.05.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 23 Jul 2019 11:05:13 -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="YQ/N0Xsa"; 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 8D21821926; Tue, 23 Jul 2019 18:05:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563905113; bh=rAlMUYDiLSqWc5h78CMWYXPZl9tMbGMy0McuERVfjeM=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=YQ/N0Xsar7YCkc6u4JNaNtp4JIHg+jQXNIQIJCS7xOhoo207XnXIzqsVtVuxY7wLF 9E2skJ1Vz2dpuFqSqtBoD0CQdgr5fKlGVFBsGVQ4rvgUs8aCpXTxC1LuCQDMvzmbEl QNhSlpOtHcSJAQlqy6VWJcmic4GO09KGFW22MRcY= 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 14:05:11 -0400 In-Reply-To: <20190723175543.GL363@bombadil.infradead.org> References: <20190723131212.445-1-jlayton@kernel.org> <3622a5fe9f13ddfd15b262dbeda700a26c395c2a.camel@kernel.org> <20190723175543.GL363@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 10:55 -0700, Matthew Wilcox wrote: > On Tue, Jul 23, 2019 at 01:52:36PM -0400, Jeff Layton wrote: > > On Tue, 2019-07-23 at 09:12 -0400, Jeff Layton wrote: > > > A lot of callers of kvfree only go down the vfree path under very rare > > > circumstances, and so may never end up hitting the might_sleep_if in it. > > > Ensure that when kvfree is called, that it is operating in a context > > > where it is allowed to sleep. > > > > > > Cc: Alexander Viro > > > Cc: Luis Henriques > > > Signed-off-by: Jeff Layton > > > --- > > > mm/util.c | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > > FWIW, I started looking at this after Luis sent me some ceph patches > > that fixed a few of these problems. I have not done extensive testing > > with this patch, so maybe consider this an RFC for now. > > > > 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. -- Jeff Layton