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b=I0yypgztqHYHudhBA6ByA6knGUXoboWc2PlZ+XhbgEniQWl5akFhn6IQfYkd0Wjs0 qzicJi12uTR2v/UKr+qFY1E8mPeqnhsdaOtVJTp3dneWEig21BSimo5UF+BK+I+9za nlxGMqFz02xAG9LswMnw6XagAmh5CgBNpNQJfpjIUsjC9ri+p3ffDv6p27A5MrhcnN CVPkmxdMWa4791DvD7t1j0H9Z0BXrcsyEzrihEoEu1U7E6pCG4ci9EQRNg8NGsV3UC pD0uRqd4L6kvqBNSlWlv/mnKeA7blIVJ0NCiXQ1/h1YUBJfRcnHEt7DNWMheLyKXtL i55ZzeVDmRqHg== From: Sasha Levin To: stable@vger.kernel.org, kartikey406@gmail.com Cc: syzbot+d8d4c31d40f868eaea30@syzkaller.appspotmail.com, Uladzislau Rezki , Hillf Danton , Andrew Morton , linux-mm@kvack.org Subject: FAILED: Patch "mm/vmalloc: prevent RCU stalls in kasan_release_vmalloc_node" failed to apply to 5.15-stable tree Date: Sat, 28 Feb 2026 20:52:24 -0500 Message-ID: <20260301015225.1718913-1-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 MIME-Version: 1.0 X-Patchwork-Hint: ignore X-stable: review Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: snq8ab5ty5iiye3tyiycb4oki4yqmd3g X-Rspamd-Queue-Id: 03F39180007 X-Rspamd-Server: rspam03 X-HE-Tag: 1772329947-192879 X-HE-Meta: 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 XZz6SX7w 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From 5747435e0fd474c24530ef1a6822f47e7d264b27 Mon Sep 17 00:00:00 2001 From: Deepanshu Kartikey Date: Mon, 12 Jan 2026 16:06:12 +0530 Subject: [PATCH] mm/vmalloc: prevent RCU stalls in kasan_release_vmalloc_node 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. Link: https://lkml.kernel.org/r/20260112103612.627247-1-kartikey406@gmail.com Signed-off-by: Deepanshu Kartikey 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 Reviewed-by: Uladzislau Rezki (Sony) Cc: Hillf Danton Cc: Signed-off-by: Andrew Morton --- mm/vmalloc.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 32d6ee92d4ff8..ca4c653286870 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2273,11 +2273,14 @@ 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; @@ -2287,6 +2290,11 @@ 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); -- 2.51.0