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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id br15si19593520pjb.13.2019.07.26.17.38.54 for (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 26 Jul 2019 17:38:54 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=seLQcuWQ; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=vX3HX++H8FmKlfKaZ9xE3OKPlAYHgui3BNbzlA6WfOg=; b=seLQcuWQ9l+ahJ/jJ2TW3xmNh 8Fd8u4bC+a2yPgf1X9h7DGdfz5aKukAwbQ56fEWeWFKaQX5/debmR9XWEoLpFFpNDpl9+sH0joFjQ JnacKLuSYm1Sg7A6gpvQYt6mK/aPakD1pHE/JlEp1zNtGDotoemVv3jHEX+NsYwmUKwth+cAUcTf3 zOs8gNyo88rzJacIINOX4ZKDI+WyAEVwm+mE+5JRGRmjU+CFfSfTMl+mHFMzQp7Cw8+FreQcZz8AX 4S4B6nECv/VkG2VAjx9OuCPO6Us+aG7MLIWXfT2aeTf2Ml+k9vwu7UR2hZB3A6zcEmoT5g0jDFkDp TUiPBSwDQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1hrAjb-0007V1-Ak; Sat, 27 Jul 2019 00:38:51 +0000 Date: Fri, 26 Jul 2019 17:38:51 -0700 From: Matthew Wilcox To: Jeff Layton Cc: Alexander Duyck , Andrew Morton , linux-mm , LKML , Alexander Viro , Luis Henriques , Christoph Hellwig , Carlos Maiolino Subject: Re: [PATCH] mm: Make kvfree safe to call Message-ID: <20190727003851.GJ30641@bombadil.infradead.org> References: <20190726210137.23395-1-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.4 (2019-03-13) 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 Fri, Jul 26, 2019 at 05:25:03PM -0400, Jeff Layton wrote: > On Fri, 2019-07-26 at 14:10 -0700, Alexander Duyck wrote: > > On Fri, Jul 26, 2019 at 2:01 PM Matthew Wilcox wrote: > > > From: "Matthew Wilcox (Oracle)" > > > > > > Since vfree() can sleep, calling kvfree() from contexts where sleeping > > > is not permitted (eg holding a spinlock) is a bit of a lottery whether > > > it'll work. Introduce kvfree_safe() for situations where we know we can > > > sleep, but make kvfree() safe by default. > > > > > > Reported-by: Jeff Layton > > > Cc: Alexander Viro > > > Cc: Luis Henriques > > > Cc: Christoph Hellwig > > > Cc: Carlos Maiolino > > > Signed-off-by: Matthew Wilcox (Oracle) > > > > So you say you are adding kvfree_safe() in the patch description, but > > it looks like you are introducing kvfree_fast() below. Did something > > change and the patch description wasn't updated, or is this just the > > wrong description for this patch? Oops, bad description. Thanks, I'll fix it for v2. > > > +/** > > > + * kvfree_fast() - Free memory. > > > + * @addr: Pointer to allocated memory. > > > + * > > > + * kvfree_fast frees memory allocated by any of vmalloc(), kmalloc() or > > > + * kvmalloc(). It is slightly more efficient to use kfree() or vfree() if > > > + * you are certain that you know which one to use. > > > + * > > > + * Context: Either preemptible task context or not-NMI interrupt. Must not > > > + * hold a spinlock as it can sleep. > > > + */ > > > +void kvfree_fast(const void *addr) > > > +{ > > > + might_sleep(); > > > + > > might_sleep_if(!in_interrupt()); > > That's what vfree does anyway, so we might as well exempt the case where > you are. True, but if we are in interrupt, then we may as well call kvfree() since it'll do the same thing, and this way the rules are clearer. > > > + if (is_vmalloc_addr(addr)) > > > + vfree(addr); > > > + else > > > + kfree(addr); > > > +} > > > +EXPORT_SYMBOL(kvfree_fast); > > > + > > That said -- is this really useful? > > The only way to know that this is safe is to know what sort of > allocation it is, and in that case you can just call kfree or vfree as > appropriate. It's safe if you know you're not holding any spinlocks, for example ...