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 810F540BFD for ; Mon, 19 Feb 2024 18:54:33 +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=1708368873; cv=none; b=HH5bdEWuzbDX+mDykJ+mFIjGYCmn3Y/jAqnDgOolgdMXVy2ZAPe/YFYkKpUEib+8jgLm9flkY9Kad0bT3UKTB38IcoYzphBZa8xh3Twmi8GnEjJh6fHBg/le/HfeF/4xsGZVZhC/87xRtwkE19/hr+4x80M6sJWydTSYtU4yJBA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708368873; c=relaxed/simple; bh=KdzrcpEn0EKwKla8/8KhIbhcwEOiI5rYF+5wC88vnog=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=uYBSvEnZuu8lBg/aA5oc//5cNZQiRGpCoPdceezpkSzD9xB5wdkIl4msSCHOwfUnn4lD3HVYJjlBlp+Bfo05hBkL5FXHaS/cYhlOdsXHveEXcGcjCjjfCXemqg0R72H5HUNmQNK5+2F5jWtMdjY9DNssNwsERi87Fm/0eyY21yo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=u9jDl0Cy; 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="u9jDl0Cy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A75FFC433C7; Mon, 19 Feb 2024 18:54:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1708368873; bh=KdzrcpEn0EKwKla8/8KhIbhcwEOiI5rYF+5wC88vnog=; h=Subject:To:Cc:From:Date:From; b=u9jDl0CyRvc5FbcfsA+/LFfLX1AmUSMLoIiPARnZRlFMbkcxJolJhSZukL3wemihn 027k0ki/wnOjIMqQe9bHkssAYJpWxRMMyHW3yPtKCwf8UA2t4Fqb7LCqL6ACHCAaK6 K3jYSumkLpsA+ULmpjQB8F8tC4Xi3lQmWn4unfwc= Subject: FAILED: patch "[PATCH] fs/proc: do_task_stat: use sig->stats_lock to gather the" failed to apply to 6.1-stable tree To: oleg@redhat.com,akpm@linux-foundation.org,dylanbhatch@google.com,ebiederm@xmission.com,stable@vger.kernel.org Cc: From: Date: Mon, 19 Feb 2024 19:54:19 +0100 Message-ID: <2024021919-chrome-doorframe-66ed@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 6.1-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-6.1.y git checkout FETCH_HEAD git cherry-pick -x 7601df8031fd67310af891897ef6cc0df4209305 # git commit -s git send-email --to '' --in-reply-to '2024021919-chrome-doorframe-66ed@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^.. Possible dependencies: 7601df8031fd ("fs/proc: do_task_stat: use sig->stats_lock to gather the threads/children stats") 60f92acb60a9 ("fs/proc: do_task_stat: move thread_group_cputime_adjusted() outside of lock_task_sighand()") 7904e53ed5a2 ("fs/proc: do_task_stat: use __for_each_thread()") thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 7601df8031fd67310af891897ef6cc0df4209305 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Tue, 23 Jan 2024 16:33:57 +0100 Subject: [PATCH] fs/proc: do_task_stat: use sig->stats_lock to gather the threads/children stats lock_task_sighand() can trigger a hard lockup. If NR_CPUS threads call do_task_stat() at the same time and the process has NR_THREADS, it will spin with irqs disabled O(NR_CPUS * NR_THREADS) time. Change do_task_stat() to use sig->stats_lock to gather the statistics outside of ->siglock protected section, in the likely case this code will run lockless. Link: https://lkml.kernel.org/r/20240123153357.GA21857@redhat.com Signed-off-by: Oleg Nesterov Signed-off-by: Dylan Hatch Cc: Eric W. Biederman Cc: Signed-off-by: Andrew Morton diff --git a/fs/proc/array.c b/fs/proc/array.c index 45ba91863808..34a47fb0c57f 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -477,13 +477,13 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns, int permitted; struct mm_struct *mm; unsigned long long start_time; - unsigned long cmin_flt = 0, cmaj_flt = 0; - unsigned long min_flt = 0, maj_flt = 0; - u64 cutime, cstime, utime, stime; - u64 cgtime, gtime; + unsigned long cmin_flt, cmaj_flt, min_flt, maj_flt; + u64 cutime, cstime, cgtime, utime, stime, gtime; unsigned long rsslim = 0; unsigned long flags; int exit_code = task->exit_code; + struct signal_struct *sig = task->signal; + unsigned int seq = 1; state = *get_task_state(task); vsize = eip = esp = 0; @@ -511,12 +511,8 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns, sigemptyset(&sigign); sigemptyset(&sigcatch); - cutime = cstime = 0; - cgtime = gtime = 0; if (lock_task_sighand(task, &flags)) { - struct signal_struct *sig = task->signal; - if (sig->tty) { struct pid *pgrp = tty_get_pgrp(sig->tty); tty_pgrp = pid_nr_ns(pgrp, ns); @@ -527,27 +523,9 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns, num_threads = get_nr_threads(task); collect_sigign_sigcatch(task, &sigign, &sigcatch); - cmin_flt = sig->cmin_flt; - cmaj_flt = sig->cmaj_flt; - cutime = sig->cutime; - cstime = sig->cstime; - cgtime = sig->cgtime; rsslim = READ_ONCE(sig->rlim[RLIMIT_RSS].rlim_cur); - /* add up live thread stats at the group level */ if (whole) { - struct task_struct *t; - - __for_each_thread(sig, t) { - min_flt += t->min_flt; - maj_flt += t->maj_flt; - gtime += task_gtime(t); - } - - min_flt += sig->min_flt; - maj_flt += sig->maj_flt; - gtime += sig->gtime; - if (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_STOP_STOPPED)) exit_code = sig->group_exit_code; } @@ -562,6 +540,34 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns, if (permitted && (!whole || num_threads < 2)) wchan = !task_is_running(task); + do { + seq++; /* 2 on the 1st/lockless path, otherwise odd */ + flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq); + + cmin_flt = sig->cmin_flt; + cmaj_flt = sig->cmaj_flt; + cutime = sig->cutime; + cstime = sig->cstime; + cgtime = sig->cgtime; + + if (whole) { + struct task_struct *t; + + min_flt = sig->min_flt; + maj_flt = sig->maj_flt; + gtime = sig->gtime; + + rcu_read_lock(); + __for_each_thread(sig, t) { + min_flt += t->min_flt; + maj_flt += t->maj_flt; + gtime += task_gtime(t); + } + rcu_read_unlock(); + } + } while (need_seqretry(&sig->stats_lock, seq)); + done_seqretry_irqrestore(&sig->stats_lock, seq, flags); + if (whole) { thread_group_cputime_adjusted(task, &utime, &stime); } else {