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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id n81si19413731pfb.258.2019.05.20.07.23.34 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 20 May 2019 07:23:34 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of batv+dfc7240828d5493a4f00+5748+infradead.org+hch@bombadil.srs.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=F6Qxfkwn; spf=pass (google.com: best guess record for domain of batv+dfc7240828d5493a4f00+5748+infradead.org+hch@bombadil.srs.infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=BATV+dfc7240828d5493a4f00+5748+infradead.org+hch@bombadil.srs.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=OatVHIrCWYguW9Na7RTRuHTBGkcI0B4NqgZ1cLxhQgQ=; b=F6QxfkwnuYixy1VbMF0FyONlO dsWCZHGjFMaTg+CXsiL17P09p9tVTwmdejillTJOVKTk/anWvWL7/2Hjnuh5LWjmsNBcyVvck9ejw qRag5Wnz4m1LXhBpxrUmjVbrTKqVDVxM3SLJ5hRyo/66WXxDBVFYyNwcKp+0msVjFMiON4shXUf5H vbUY6T4yOTY7RrgQqYAH4p/LVBT6jkqdtXedMJk6ExQoBvbX8XFofYNevHhct2O6nnOdHeb742/3u cTM60s4nWRGiMl3Wt1xdFEVJ5qZgbUd+XZapkxqz3GuRKvPS5fpJirF6QQ06yJccuyRVkv3a1PPwd Mke8wj0lw==; Received: from hch by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1hSjCN-0003ZB-Ee; Mon, 20 May 2019 14:23:31 +0000 Date: Mon, 20 May 2019 07:23:31 -0700 From: Christoph Hellwig To: Alan Stern Cc: Christoph Hellwig , Oliver Neukum , Jaewon Kim , linux-mm@kvack.org, gregkh@linuxfoundation.org, Jaewon Kim , m.szyprowski@samsung.com, ytk.lee@samsung.com, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Subject: Re: [RFC PATCH] usb: host: xhci: allow __GFP_FS in dma allocation Message-ID: <20190520142331.GA12108@infradead.org> References: <20190520101206.GA9291@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html 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 Mon, May 20, 2019 at 10:16:57AM -0400, Alan Stern wrote: > What if the allocation requires the kernel to swap some old pages out > to the backing store, but the backing store is on the device that the > driver is managing? The swap can't take place until the current I/O > operation is complete (assuming the driver can handle only one I/O > operation at a time), and the current operation can't complete until > the old pages are swapped out. Result: deadlock. > > Isn't that the whole reason for using GFP_NOIO in the first place? It is, or rather was. As it has been incredibly painful to wire up the gfp_t argument through some callstacks, most notably the vmalloc allocator which is used by a lot of the DMA allocators on non-coherent platforms, we now have the memalloc_noio_save and memalloc_nofs_save functions that mark a thread as not beeing to go into I/O / FS reclaim. So even if you use GFP_KERNEL you will not dip into reclaim with those flags set on the thread.