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[109.81.83.72]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5bebc0812a3sm5401160a12.82.2024.08.19.03.19.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Aug 2024 03:19:30 -0700 (PDT) Date: Mon, 19 Aug 2024 12:19:30 +0200 From: Michal Hocko To: David Hildenbrand Cc: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, 42.hyeyoo@gmail.com, cl@linux.com, hailong.liu@oppo.com, hch@infradead.org, iamjoonsoo.kim@lge.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, torvalds@linux-foundation.org, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, virtualization@lists.linux.dev, Lorenzo Stoakes , Kees Cook , Eugenio =?iso-8859-1?Q?P=E9rez?= , Jason Wang , Maxime Coquelin , "Michael S. Tsirkin" , Xuan Zhuo Subject: Re: [PATCH v3 4/4] mm: prohibit NULL deference exposed for unsupported non-blockable __GFP_NOFAIL Message-ID: References: <20240817062449.21164-1-21cnbao@gmail.com> <20240817062449.21164-5-21cnbao@gmail.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon 19-08-24 11:44:39, David Hildenbrand wrote: [...] > > 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 > > + * All existing users of the __GFP_NOFAIL are blockable > > + * otherwise we introduce a busy loop with inside the page > > + * allocator from non-sleepable contexts > > */ > > - if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask)) > > - goto fail; > > + BUG_ON(!can_direct_reclaim); > > No new BUG_ON(), WARN_ON_ONCE() is good enough for something that should be > found during ordinary testing. Do you mean if (WARN_ON_ONCE_GFP(...)) goto retry? Barry has mentioned that option in the changelog. -- Michal Hocko SUSE Labs