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Tsirkin" , Xuan Zhuo Subject: [PATCH v4 2/3] mm: document __GFP_NOFAIL must be blockable Date: Sat, 31 Aug 2024 08:28:22 +1200 Message-Id: <20240830202823.21478-3-21cnbao@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240830202823.21478-1-21cnbao@gmail.com> References: <20240830202823.21478-1-21cnbao@gmail.com> MIME-Version: 1.0 X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 191B740015 X-Stat-Signature: 7h7g4uzsc9uwfiactehxqharbc1fuqeb X-HE-Tag: 1725049769-497410 X-HE-Meta: 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 xyudLPKZ 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 pr/XROv6 oRmtUcHgEcWGWcdzrGoSe8qffvrVlBGzBM0YkMBK3GI= 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 Acked-by: David Hildenbrand --- 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