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 E66D82DF9F; Tue, 20 Feb 2024 21:41:42 +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=1708465303; cv=none; b=Wj79vHuDjAKiWwKk3wL0fyIeBrVKkrQaLxduQlt8QYQoo++fcd6PZmNdnZZka7JzVCyPjlnymPNmqY+Q/WOY0JCt9pZNshcqbfPp9Ot/mNgFt/Wg/Vw63oX4iznwRksNHDYZeyKTyi7hcNv1z7QkHN+NMevrV5pHkjZ8hjNn/Hw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708465303; c=relaxed/simple; bh=TKjNbibahII93IRQEoz9EPuQPtCUKRF7xIMvkOKAZPo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=KzIl1URvC2Td6jD8LQJNSvj+YsC2mvG7F7LkFIdgTO9coig4/2unV/kisxjB8NWcfLieJkjOqXF4f1FYFWz3/i9+mTO1n1QR7giVLAEb+MWE5gbN5Ko9C8eeKULhc64uDbEx1Yg2mQmKKt01MAXkAmRQGpw3qOOlx4XsKkP3iCA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=V8OYUfFp; 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="V8OYUfFp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 63C00C433F1; Tue, 20 Feb 2024 21:41:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1708465302; bh=TKjNbibahII93IRQEoz9EPuQPtCUKRF7xIMvkOKAZPo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=V8OYUfFp3ZltlijeIXuDRlUtyWUGICKOTzTXHVt7Bbg9zmniorzyalFr0o7HcYeJL CQJ2V/G8Jc8eUTOPfLTamyjm84u33BgsiFNFyAgooXnMnDBDBk5tbMu8xX/wlcGADo oExCLQGo7g07GIeUz0pU+TQEyrIurf66clI2B+go= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Oleg Nesterov , Dylan Hatch , "Eric W. Biederman" , Andrew Morton Subject: [PATCH 6.7 301/309] fs/proc: do_task_stat: use sig->stats_lock to gather the threads/children stats Date: Tue, 20 Feb 2024 21:57:40 +0100 Message-ID: <20240220205642.515753263@linuxfoundation.org> X-Mailer: git-send-email 2.43.2 In-Reply-To: <20240220205633.096363225@linuxfoundation.org> References: <20240220205633.096363225@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.7-stable review patch. If anyone has any objections, please let me know. ------------------ From: Oleg Nesterov commit 7601df8031fd67310af891897ef6cc0df4209305 upstream. 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 Signed-off-by: Greg Kroah-Hartman --- fs/proc/array.c | 58 ++++++++++++++++++++++++++++++-------------------------- 1 file changed, 32 insertions(+), 26 deletions(-) --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -477,13 +477,13 @@ static int do_task_stat(struct seq_file 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 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 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 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 {