From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AA025314D16 for ; Tue, 3 Feb 2026 12:42:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770122527; cv=none; b=sR3mskRmLQo3L6mdml3s6bd13AL4B8SQa48hxbJRQDl2sgsj/rhl7/XLDwiicI8ZM07pzsvJRQlQmi6K21ifUWMvaSE8yR+LChz/TaqjHDVlj4/8TiscKzu7nUvlDH/iRKzxAdH01rwJgxp6Yd4njxJe8gyhYDHQuWWEkW17aH0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770122527; c=relaxed/simple; bh=H8S3u8USiVO8sj9OSsw4jqcakrNJtZtI67SmGgG/7Hc=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=GLW74vLi/VKJx7SB3TPepUTsUXRVc6QP+Z5OThmkNqKTrJatv5XuYH/cG1huAr9URQxKdYIadPAh9LmyBVp9cuHkTspJY3lF8Y6/kHypJtMIVOUL+TOaGT4F/rUKD2jELTKRsdEdFeXDU0mSeLhEyvcLjcfr95qIy+U1V496h8s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=NvdJ8oVZ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="NvdJ8oVZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AA057C116D0; Tue, 3 Feb 2026 12:42:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1770122527; bh=H8S3u8USiVO8sj9OSsw4jqcakrNJtZtI67SmGgG/7Hc=; h=Subject:To:Cc:From:Date:From; b=NvdJ8oVZKoZC+i8G0ssPNF9D0sIxWml8vwj34eC8cTgnZ+otuBTV8jiap9KkMnGsa UavfQfOa4N3tTWFYq7nirWYSpbdIl4wfwvOpbEd/8LwXsNxKNAU+nO2afKRMGJkMKI 8b6j7Az+Uqh97F9rRI2ICQYjmRIiaPtsnzxtnt7I= Subject: FAILED: patch "[PATCH] writeback: fix 100% CPU usage when dirtytime_expire_interval" failed to apply to 6.12-stable tree To: laveeshb@laveeshbansal.com,brauner@kernel.org,jack@suse.cz Cc: From: Date: Tue, 03 Feb 2026 13:42:04 +0100 Message-ID: <2026020303-ammonia-active-e64f@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.12-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 . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y git checkout FETCH_HEAD git cherry-pick -x 543467d6fe97e27e22a26e367fda972dbefebbff # git commit -s git send-email --to '' --in-reply-to '2026020303-ammonia-active-e64f@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 543467d6fe97e27e22a26e367fda972dbefebbff Mon Sep 17 00:00:00 2001 From: Laveesh Bansal Date: Tue, 6 Jan 2026 14:50:58 +0000 Subject: [PATCH] writeback: fix 100% CPU usage when dirtytime_expire_interval is 0 When vm.dirtytime_expire_seconds is set to 0, wakeup_dirtytime_writeback() schedules delayed work with a delay of 0, causing immediate execution. The function then reschedules itself with 0 delay again, creating an infinite busy loop that causes 100% kworker CPU usage. Fix by: - Only scheduling delayed work in wakeup_dirtytime_writeback() when dirtytime_expire_interval is non-zero - Cancelling the delayed work in dirtytime_interval_handler() when the interval is set to 0 - Adding a guard in start_dirtytime_writeback() for defensive coding Tested by booting kernel in QEMU with virtme-ng: - Before fix: kworker CPU spikes to ~73% - After fix: CPU remains at normal levels - Setting interval back to non-zero correctly resumes writeback Fixes: a2f4870697a5 ("fs: make sure the timestamps for lazytime inodes eventually get written") Cc: stable@vger.kernel.org Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220227 Signed-off-by: Laveesh Bansal Link: https://patch.msgid.link/20260106145059.543282-2-laveeshb@laveeshbansal.com Reviewed-by: Jan Kara Signed-off-by: Christian Brauner diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 6800886c4d10..cd21c74cd0e5 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -2492,7 +2492,8 @@ static void wakeup_dirtytime_writeback(struct work_struct *w) wb_wakeup(wb); } rcu_read_unlock(); - schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ); + if (dirtytime_expire_interval) + schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ); } static int dirtytime_interval_handler(const struct ctl_table *table, int write, @@ -2501,8 +2502,12 @@ static int dirtytime_interval_handler(const struct ctl_table *table, int write, int ret; ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); - if (ret == 0 && write) - mod_delayed_work(system_percpu_wq, &dirtytime_work, 0); + if (ret == 0 && write) { + if (dirtytime_expire_interval) + mod_delayed_work(system_percpu_wq, &dirtytime_work, 0); + else + cancel_delayed_work_sync(&dirtytime_work); + } return ret; } @@ -2519,7 +2524,8 @@ static const struct ctl_table vm_fs_writeback_table[] = { static int __init start_dirtytime_writeback(void) { - schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ); + if (dirtytime_expire_interval) + schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ); register_sysctl_init("vm", vm_fs_writeback_table); return 0; }