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a=rsa-sha256; c=relaxed/relaxed; d=stgolabs.net; s=dreamhost; t=1722726555; bh=BSx4gKWGu87H42fwZ04zpF/2UtyzpgP11LfTvEbpceo=; h=Date:From:To:Cc:Subject:Content-Type; b=k7eX7c7rHLiKXeWCkXHf3djxUWtKLGOeaDrlfO8fsGZEVSGu7PxHeOBlc9WlgmqeO uZ1+QDCeEnyAdWK2Shl6u+bHPfjroCbpTs2ojW7Kt58JchGNvQB5coNmp2/7LFGomL v2C5Ubdnz0V3oz4JOeYhvssJ4DoN/RVKTr/0RrGC1zcDYGyNyY7GMJREBnY44927to Wd46B/rFr+6l6UOtbI5AWrehLgU836SJ8Xz+2xD9W3TZlA3d/OtZvGU+f+sO7ZVb// 8ww7PmE75yTZrC8A7D97dUq3LFHH5fTGS9BvJQRYALpWpAQjPuE2yj1Pbb9fSQUG8X +pffunT0MHC6g== Date: Sat, 3 Aug 2024 16:09:10 -0700 From: Davidlohr Bueso To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, 42.hyeyoo@gmail.com, cl@linux.com, hch@infradead.org, iamjoonsoo.kim@lge.com, lstoakes@gmail.com, mhocko@suse.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, virtualization@lists.linux.dev, hailong.liu@oppo.com, torvalds@linux-foundation.org Subject: Re: [PATCH 2/5] mm: Document __GFP_NOFAIL must be blockable Message-ID: Mail-Followup-To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, 42.hyeyoo@gmail.com, cl@linux.com, hch@infradead.org, iamjoonsoo.kim@lge.com, lstoakes@gmail.com, mhocko@suse.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, virtualization@lists.linux.dev, hailong.liu@oppo.com, torvalds@linux-foundation.org References: <20240724085544.299090-1-21cnbao@gmail.com> <20240724085544.299090-3-21cnbao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20240724085544.299090-3-21cnbao@gmail.com> User-Agent: NeoMutt/20240425 X-Rspamd-Queue-Id: 45F52180011 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 9eyji44jxq6eb1me3i7i1rxidzim1nzm X-HE-Tag: 1722726557-634882 X-HE-Meta: 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 LetuqLmH M7P8dkQLGn08fyWfnTycOyfG8J0gPUrQQ6jNjqoMQ5IQyZWny6z4wWR6XkxiU4zIvgORWefYVrRF2yGRyrQmfLFDQgfCc0MTnL7QdtspnK+ETkFFMAZoyJUbIhWgtTkGdvNKTXm70R03SwxgS6+ulpc5tAMcmEj7PnYuGqnZQjYJaAmTFOLmG1i9BYVu3RpGBNjpMrJfi0VZBC7DfaKvPEgO6yVqAcFds577w70SSU+5V8rzea4AV2bmzNcj6N/wzv6uZ39tpTxCpCclQD6vbDUGX/S7tRr/FQ0Q+qGuiE94KE+dvdv1WS4FovDyqehzvOChGf22mWlSa5dYG6uom2qDqKK3cQHLSGfIhHK2ki13P/fjb+7270jcNr7Rh3uMs2OcybYyByfDOAcVBr/W4C6BFL4in6/V6IzxDgq93FNg5l+fYbB0wKsUCjtOLUxYwViZXvsqUTrxpLbORurwxacGMBbaP9S3J0kMEwJ1XxpOtrSZMA/kr/XJvq9DFu86Ax4R5 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: List-Subscribe: List-Unsubscribe: On Wed, 24 Jul 2024, Barry Song wrote:\n >From: Barry Song > >Non-blocking allocation with __GFP_NOFAIL is not supported and may >still result in NULL pointers (if we don't return NULL, we result >in busy-loop within non-sleepable contexts): > >static inline struct page * >__alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > struct alloc_context *ac) >{ > ... > /* > * Make sure that __GFP_NOFAIL request doesn't leak out and make sure > * we always retry > */ > if (gfp_mask & __GFP_NOFAIL) { > /* > * All existing users of the __GFP_NOFAIL are blockable, so warn > * of any new users that actually require GFP_NOWAIT > */ > if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask)) > goto fail; > ... > } > ... >fail: > warn_alloc(gfp_mask, ac->nodemask, > "page allocation failure: order:%u", order); >got_pg: > return page; >} > >Highlight this in the documentation of __GFP_NOFAIL so that non-mm >subsystems can reject any illegal usage of __GFP_NOFAIL with >GFP_ATOMIC, GFP_NOWAIT, etc. > Acked-by: Davidlohr Bueso