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AJvYcCWhzGEcZCzkN5UYCgQbk2murmDc0AcLoCe+uywwA6xk0y+eqO6xn3LskoPeawXyzxE0drlK9ZQdDg7gN189j+dG3jg= X-Gm-Message-State: AOJu0YwfxQFz04yO00db2LjU+rq/pWow2vor2Y9XNtvNtkZh7uN2ddXd UQas9wwiy36gEW9doHhrZY9hA8T57682yYDKNYK9VUZu50nfXRYY X-Google-Smtp-Source: AGHT+IGub7/cT356oygu2KYD+sWoBYGAcDkpV7grhrgXGzsfW0LOrUdda5GHWr7u45BFlKT/uocwXg== X-Received: by 2002:a05:6a00:949a:b0:706:aa39:d5c1 with SMTP id d2e1a72fcca58-70efe44f70bmr5615340b3a.8.1722384176485; Tue, 30 Jul 2024 17:02:56 -0700 (PDT) Received: from localhost.localdomain ([2407:7000:8942:5500:aaa1:59ff:fe57:eb97]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70ead6e1a2asm8871689b3a.23.2024.07.30.17.02.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Jul 2024 17:02:56 -0700 (PDT) From: Barry Song <21cnbao@gmail.com> To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: 42.hyeyoo@gmail.com, cl@linux.com, hailong.liu@oppo.com, hch@infradead.org, iamjoonsoo.kim@lge.com, lstoakes@gmail.com, mhocko@suse.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 Subject: [PATCH v2 2/4] mm: Document __GFP_NOFAIL must be blockable Date: Wed, 31 Jul 2024 12:01:53 +1200 Message-Id: <20240731000155.109583-3-21cnbao@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240731000155.109583-1-21cnbao@gmail.com> References: <20240731000155.109583-1-21cnbao@gmail.com> MIME-Version: 1.0 X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: E24811C0030 X-Stat-Signature: 9owui4zu6x4yfqb1zx9de93dqjkrfetd X-HE-Tag: 1722384177-772055 X-HE-Meta: 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 gwDvKdu4 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 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: 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: Michal Hocko Signed-off-by: Barry Song Acked-by: Vlastimil Babka Reviewed-by: Christoph Hellwig --- include/linux/gfp_types.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h index 313be4ad79fd..4a1fa7706b0c 100644 --- a/include/linux/gfp_types.h +++ b/include/linux/gfp_types.h @@ -215,7 +215,8 @@ enum { * the caller still has to check for failures) while costly requests try to be * not disruptive and back off even without invoking the OOM killer. * The following three modifiers might be used to override some of these - * implicit rules. + * implicit rules. Please note that all of them must be used along with + * %__GFP_DIRECT_RECLAIM flag. * * %__GFP_NORETRY: The VM implementation will try only very lightweight * memory direct reclaim to get some memory under memory pressure (thus @@ -246,6 +247,8 @@ enum { * cannot handle allocation failures. The allocation could block * indefinitely but will never return with failure. Testing for * failure is pointless. + * It _must_ be blockable and used together with __GFP_DIRECT_RECLAIM. + * It should _never_ be used in non-sleepable contexts. * New users should be evaluated carefully (and the flag should be * used only when there is no reasonable failure policy) but it is * definitely preferable to use the flag rather than opencode endless