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([2405:201:682f:389d:7751:dfe4:62a3:f9d2]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a3e3cc8ddfsm170993495ad.74.2026.01.12.02.36.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jan 2026 02:36:18 -0800 (PST) From: Deepanshu Kartikey To: akpm@linux-foundation.org, urezki@gmail.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+d8d4c31d40f868eaea30@syzkaller.appspotmail.com Subject: [PATCH v2] mm/vmalloc: prevent RCU stalls in kasan_release_vmalloc_node Date: Mon, 12 Jan 2026 16:06:12 +0530 Message-ID: <20260112103612.627247-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: A6EEE20006 X-Rspamd-Server: rspam06 X-Stat-Signature: pq88g8m3kgeresfqdnftgubksk91xena X-Rspam-User: X-HE-Tag: 1768214180-98351 X-HE-Meta: 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 jthoBXJf 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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: When CONFIG_PAGE_OWNER is enabled, freeing KASAN shadow pages during vmalloc cleanup triggers expensive stack unwinding that acquires RCU read locks. Processing a large purge_list without rescheduling can cause the task to hold CPU for extended periods (10+ seconds), leading to RCU stalls and potential OOM conditions. The issue manifests in purge_vmap_node() -> kasan_release_vmalloc_node() where iterating through hundreds or thousands of vmap_area entries and freeing their associated shadow pages causes: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P6229/1:b..l ... task:kworker/0:17 state:R running task stack:28840 pid:6229 ... kasan_release_vmalloc_node+0x1ba/0xad0 mm/vmalloc.c:2299 purge_vmap_node+0x1ba/0xad0 mm/vmalloc.c:2299 Each call to kasan_release_vmalloc() can free many pages, and with page_owner tracking, each free triggers save_stack() which performs stack unwinding under RCU read lock. Without yielding, this creates an unbounded RCU critical section. Add periodic cond_resched() calls within the loop to allow: - RCU grace periods to complete - Other tasks to run - Scheduler to preempt when needed The fix uses need_resched() for immediate response under load, with a batch count of 32 as a guaranteed upper bound to prevent worst-case stalls even under light load. Reported-by: syzbot+d8d4c31d40f868eaea30@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=d8d4c31d40f868eaea30 Link: https://lore.kernel.org/all/20260112084723.622910-1-kartikey406@gmail.com/T/ [v1] Suggested-by: Uladzislau Rezki Signed-off-by: Deepanshu Kartikey --- v2: Use a macro for batch size (suggested by Uladzislau Rezki) --- mm/vmalloc.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 41dd01e8430c..51e58701565d 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2268,11 +2268,14 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay) reclaim_list_global(&decay_list); } +#define KASAN_RELEASE_BATCH_SIZE 32 + static void kasan_release_vmalloc_node(struct vmap_node *vn) { struct vmap_area *va; unsigned long start, end; + unsigned int batch_count = 0; start = list_first_entry(&vn->purge_list, struct vmap_area, list)->va_start; end = list_last_entry(&vn->purge_list, struct vmap_area, list)->va_end; @@ -2282,6 +2285,11 @@ kasan_release_vmalloc_node(struct vmap_node *vn) kasan_release_vmalloc(va->va_start, va->va_end, va->va_start, va->va_end, KASAN_VMALLOC_PAGE_RANGE); + + if (need_resched() || (++batch_count >= KASAN_RELEASE_BATCH_SIZE)) { + cond_resched(); + batch_count = 0; + } } kasan_release_vmalloc(start, end, start, end, KASAN_VMALLOC_TLB_FLUSH); -- 2.43.0