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Tsirkin" , Xuan Zhuo Subject: [PATCH v3 2/4] mm: document __GFP_NOFAIL must be blockable Date: Sat, 17 Aug 2024 18:24:47 +1200 Message-Id: <20240817062449.21164-3-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20240817062449.21164-1-21cnbao@gmail.com> References: <20240817062449.21164-1-21cnbao@gmail.com> MIME-Version: 1.0 X-Stat-Signature: s7m8obm8dgy7g7q55puxkxcta7ynadef X-Rspamd-Queue-Id: 31FDD40014 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1723875922-719090 X-HE-Meta: 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 V4NRZVKX 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 zuwTasmy uySDF2QueCqbvG9ya/1JRimOzwcWGHcYy0D+dr6//ik= 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. Signed-off-by: Barry Song Acked-by: Michal Hocko Reviewed-by: Christoph Hellwig Acked-by: Vlastimil Babka Acked-by: Davidlohr Bueso Cc: Christoph Lameter Cc: David Rientjes Cc: "Eugenio Pérez" Cc: Hailong.Liu Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: Jason Wang Cc: Joonsoo Kim Cc: Kees Cook Cc: Linus Torvalds Cc: Lorenzo Stoakes Cc: Maxime Coquelin Cc: "Michael S. Tsirkin" Cc: Pekka Enberg Cc: Roman Gushchin Cc: Uladzislau Rezki (Sony) Cc: Xuan Zhuo --- 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