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Tue, 08 Sep 2026 06:13:52 -0700 (PDT) Received: from [127.0.0.1] ([2a09:bac6:37a9:1e5a::306:1]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c260d6e1c93sm625170866b.63.2026.09.08.06.13.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Sep 2026 06:13:52 -0700 (PDT) From: Caleb Kan Date: Tue, 08 Sep 2026 14:13:34 +0100 Subject: [PATCH RFC v2 01/11] stackdepot: stop preallocating after the final pool MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260908-stackdepot-trie-v2-1-1996d5cef732@cloudflare.com> References: <20260908-stackdepot-trie-v2-0-1996d5cef732@cloudflare.com> In-Reply-To: <20260908-stackdepot-trie-v2-0-1996d5cef732@cloudflare.com> To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, Vlastimil Babka , Alexander Potapenko , Marco Elver , Dmitry Vyukov , Andrey Konovalov , Oscar Salvador , Caleb Kan , kernel-team@cloudflare.com X-Mailer: b4 0.16.0 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: A65B640003 X-Rspam-User: X-Stat-Signature: pop8xy8gbccg64m8j3jf9q5a31bkwhkx X-HE-Tag: 1788873233-548880 X-HE-Meta: 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 clJg3DHZ DUYGeaWaZFsDRFFdlVjE03DFt6OH3Hco+xRD4v+2FMxVdmUJ/84UIgPFVn77dnNHdMIJOdOp2ynBHBY2+5IECw3nZFLhqyGNLX43cmLpT07ysCfGd6efi6vQoFBWa9uB1DwAxYG9a9HVJA8ylhiTvOOPPfWi6I5NwpV2wsmWazboiOxUtb8XJizMdY4Se+hKyEuXxubaciryov16R0n6tEO/T5LxeIFGKa63UbM2VOH8mmvjn1XmDQRB8QADu0YIYWL3hU6VIQ/lHWCi5sfOxWArKTQu1512Ll8rJP5PGiPORC0zcZxMBhkPiCv66vJzOd2bTBbNt4GfV4QolMeoXnqKRWCdV/ZIEEHXgmnoEmFQJcukeIjkHVLj0eA57d6QEL14aNvjVHm2z6d5nSKWmELYH05/w+uZdysx2lY5aLpR+qiA2/Llx52Hop1SC18pdTBmB6Qxj7dkRGxD0ynqsiApretdqIyXOBIjT Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Caleb Kan depot_init_pool() decides whether another pool is needed before it increments pools_num. When it registers the last allowed pool, pools_num is still one below stack_max_pools, so the existing comparison clears new_pool. With new_pool cleared, stack_depot_save_flags() can allocate another order-2 pool after a lookup miss. depot_keep_new_pool() retains its pointer in the global new_pool, so the allocation is not lost. However, pools_num has already reached stack_max_pools, and depot_init_pool() rejects every attempt to register the pool. It remains allocated and unusable until reboot. The non-NULL pointer prevents later saves from allocating more spare pools. Account for the pool being registered in the limit check so registering the final pool installs STACK_DEPOT_POISON and prevents the extra allocation. Fixes: 31639fd6cebd ("stackdepot: use variable size records for non-evictable entries") Signed-off-by: Caleb Kan --- lib/stackdepot.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/stackdepot.c b/lib/stackdepot.c index dd2717ff94bf..90c52f2e0d3f 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -323,7 +323,7 @@ static bool depot_init_pool(void **prealloc) * NULL; do not reset to NULL if we have reached the maximum number of * pools. */ - if (pools_num < stack_max_pools) + if (pools_num + 1 < stack_max_pools) WRITE_ONCE(new_pool, NULL); else WRITE_ONCE(new_pool, STACK_DEPOT_POISON); -- Git-155)