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b=K15GfRyG7ZweUGIeml9tHNQK+uRqb7MHz+nn+1IIGjT1Gc/Em8zM9BNbrCRWwqjzX HL7zlpEwzZlSmTYODx9szaKri5A69EeG8fj5Fb7JFUAQ+tJ/ydf/AsSUG2E7okjsEm QiKvTR+3kqzC/L1wxlGgrG0uA8+wNa0mWouW4m1RXFq+Cu1BsViEbPZC7T9FZrwQ4j A6kmedgDweKe5OiYT2VrA9lww5LT3VxPpUMqe246QK/nxSYchyKOX6ltS+4ZVG2htH 8u551/fqLWsieofpWVmWKzkuPgK6WNJX9FpVF+iFKFeh1IlaQtMkpVvzyIE1lae+25 Kz4z6/YD1c/hg== 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 6.6-stable tree Date: Sat, 28 Feb 2026 20:34:55 -0500 Message-ID: <20260301013456.1694526-1-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-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 1ACC480010 X-Stat-Signature: xig45y9hg4qhaw9euw18jkgbniercks7 X-HE-Tag: 1772328898-975901 X-HE-Meta: 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 QwsivBIN 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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 6.6-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