From nobody Sun Feb 8 15:59:21 2026 Received: from mail-oo1-f69.google.com (mail-oo1-f69.google.com [209.85.161.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AEFE2338904 for ; Mon, 12 Jan 2026 07:56:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.161.69 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768204590; cv=none; b=evAXLXYX7843rToXp2U5aZKBZGD1E66rzhRH0+gqtF5P4TeJa4s+blNFRlOnsBklea0I38OpRSuytSLgymPsFe8oJRFWapIXoDpBXoMLnvnliqkLrXs17zOAs0GjPE6KLUFMRidoOQjX+bI6j8ZpvkQVEohHk4J9Daik8D2wXrk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768204590; c=relaxed/simple; bh=xjzvfj5IybcQIpv4/VJIgSFS511D++cSMYNY3u0jZWM=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=DIol7ztCD2jsY9TVW9ohuFcHgHtxm2JzHU2XTnuYLqf3ohpoAmdL1YS1DBNdNlsGE6081b2pw3+x2ulAfJ6q8Qq3b4TY8yvXFUjhjtSZcY2QscwTfKkLIxL7TWuVTrzsdpQwpf/X3aUtLZXnnfLgouwlilM0sPTjtUjEPpaWXBQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com; arc=none smtp.client-ip=209.85.161.69 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com Received: by mail-oo1-f69.google.com with SMTP id 006d021491bc7-6574d3d44f9so13115217eaf.3 for ; Sun, 11 Jan 2026 23:56:28 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1768204587; x=1768809387; h=to:from:subject:message-id:in-reply-to:date:mime-version :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=KHqIE9yQ9xCpRm7Wp6KD/w7gxgCLhTvlWyVeOdl/Koo=; b=CCUNssXBkvyXrEKeBFSoRhEDdKP/HpKLqAG0rYcIsE3F+er/4fiJHLYd0eslhu1OiW ZEEcqtIEtPDdd1b/WT564A4ZzyrxLOSdmEok2E5u+29/BSXsk/G4Liu436RyquKDnt0x +mOQAHlrTvnCmYmfR37NZM4Qf+mvrlUe5TnrB2/aHvV5T7HVEbsIQGghcJmq8ewoFMoM RZ7O8g+oTwpWAscV+TBEgEPC1JSgmCDBEGRJr99Vh8IUVXknMD0SxpKBRfEN+DibYSM4 qtcM77kLp471+aixpdz98UsLrZ6DeuHgv9MkcjJAQlL6vSBm/g/iSKTpLP0Ixv2ek2YN kxTA== X-Gm-Message-State: AOJu0Yz4M8a1l4uedsiD+WS0P2ApssBbKGClcKGyEwbiQ487ZUshI+OX pm+oX7i9nYYs6J36teMtkVg05RwjUGszbxw0FRJe4ZSaLnCOi6h9nF4dm+hES8D7A+RMX7HKdBI vQmByLS9uXiMe+9qw4ZQsF8X2PVe32q0BIKQtRiH/AeHmaYeecfTk+3pv1I4= X-Google-Smtp-Source: AGHT+IFwL+kEN768LIqmDYa0SEXAhuFA1M37kbR0e+sjzkN7k/3JssOdSDfy/+wF8bxoYCwru7NWPUrm5ZRvAQh1mqXQ1V8xpmEC Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6820:1c9c:b0:65f:700a:c538 with SMTP id 006d021491bc7-65f700ad177mr2952770eaf.45.1768204587562; Sun, 11 Jan 2026 23:56:27 -0800 (PST) Date: Sun, 11 Jan 2026 23:56:27 -0800 In-Reply-To: <696487a4.050a0220.eaf7.0085.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6964a92b.050a0220.eaf7.0089.GAE@google.com> Subject: Forwarded: [PATCH] mm/vmalloc: prevent RCU stalls in kasan_release_vmalloc_node From: syzbot To: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com. *** Subject: [PATCH] mm/vmalloc: prevent RCU stalls in kasan_release_vmalloc_no= de Author: kartikey406@gmail.com #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git= master 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=3Dd8d4c31d40f868eaea30 Signed-off-by: Deepanshu Kartikey --- mm/vmalloc.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 41dd01e8430c..a9161007cf02 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2273,6 +2273,7 @@ kasan_release_vmalloc_node(struct vmap_node *vn) { struct vmap_area *va; unsigned long start, end; + unsigned int batch_count =3D 0; =20 start =3D list_first_entry(&vn->purge_list, struct vmap_area, list)->va_s= tart; end =3D list_last_entry(&vn->purge_list, struct vmap_area, list)->va_end; @@ -2282,6 +2283,11 @@ 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 >=3D 32)) { + cond_resched(); + batch_count =3D 0; + } } =20 kasan_release_vmalloc(start, end, start, end, KASAN_VMALLOC_TLB_FLUSH); --=20 2.43.0