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 601A7131733; Wed, 13 Mar 2024 16:41:16 +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=1710348077; cv=none; b=ZXHGUQ7zoKNX8l++F+uFoP1iBs6n0L6pEGOIZq0FuE007hFgM6HPxgcp9Vl/QsQAlWaXU4XtkZAAr4AnEh56NwHd4DXB6m3j9m3Az9pWrPXS+mV9ZtQnlABAycESS1B/7j1N5IrFg/DTelnnUfuH+Z5l9YUfSrkIvaYifzMjW7M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710348077; c=relaxed/simple; bh=kf81Nn6gwkP79bHbEOQ98d8m85pVfVlKTZaXwUCbYWI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=rMJTBDKfJffJ0H74lzV0OG+xgXoFX3pfe7adtSeCP0L2hYQmuimtjj3nrIJTCV6XPSnVwLHd8r2TKIppkcBOidSsXcR63Hn3Q6V+hlG9ZxbCVSwcVw9NxcNZejjNSvhzIAYphvhv78ruGJhuz6X4vOIILo3U4TJGCZqqF8CYQ3M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=e1GhBVBe; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="e1GhBVBe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E3DCFC43390; Wed, 13 Mar 2024 16:41:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1710348076; bh=kf81Nn6gwkP79bHbEOQ98d8m85pVfVlKTZaXwUCbYWI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=e1GhBVBexCqi0BMBJ9NXalj04xwuDLE7h96nq+GaPFQT0Ub9pW0kqkcMO2Wli7C0k S39K56xaw4IcolC0VzRMHJXwaJkDYg7638t+Effpw/9wCN9P2Hg/JLNCQxicSfr/SS j67bBeqYEALNrMWjNZ34mo9MQ906ecQjpuI8GAVr+P/AFLN4T/nKm8iqrSrquENv7W 5MJbcBMgBof4VLrMHOnPLpbBDjYYZLr2U1xx81WyRRM8NDlozfEPOxCH6Y3XCDc5HI 9ZoPtkoWN/5PFQxfihEJqXP64+x++aNprMW+MizaQMXg3xDGRpg7a2Y9qxUbi+K81q 5jutT5VDiCr3g== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Oleg Nesterov , Dylan Hatch , "Eric W . Biederman" , Andrew Morton , Sasha Levin Subject: [PATCH 6.1 65/71] getrusage: use sig->stats_lock rather than lock_task_sighand() Date: Wed, 13 Mar 2024 12:39:51 -0400 Message-ID: <20240313163957.615276-66-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240313163957.615276-1-sashal@kernel.org> References: <20240313163957.615276-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-KernelTest-Patch: http://kernel.org/pub/linux/kernel/v6.x/stable-review/patch-6.1.82-rc1.gz X-KernelTest-Tree: git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git X-KernelTest-Branch: linux-6.1.y X-KernelTest-Patches: git://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git X-KernelTest-Version: 6.1.82-rc1 X-KernelTest-Deadline: 2024-03-15T16:39+00:00 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit From: Oleg Nesterov [ Upstream commit f7ec1cd5cc7ef3ad964b677ba82b8b77f1c93009 ] lock_task_sighand() can trigger a hard lockup. If NR_CPUS threads call getrusage() at the same time and the process has NR_THREADS, spin_lock_irq will spin with irqs disabled O(NR_CPUS * NR_THREADS) time. Change getrusage() to use sig->stats_lock, it was specifically designed for this type of use. This way it runs lockless in the likely case. TODO: - Change do_task_stat() to use sig->stats_lock too, then we can remove spin_lock_irq(siglock) in wait_task_zombie(). - Turn sig->stats_lock into seqcount_rwlock_t, this way the readers in the slow mode won't exclude each other. See https://lore.kernel.org/all/20230913154907.GA26210@redhat.com/ - stats_lock has to disable irqs because ->siglock can be taken in irq context, it would be very nice to change __exit_signal() to avoid the siglock->stats_lock dependency. Link: https://lkml.kernel.org/r/20240122155053.GA26214@redhat.com Signed-off-by: Oleg Nesterov Reported-by: Dylan Hatch Tested-by: Dylan Hatch Cc: Eric W. Biederman Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- kernel/sys.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/kernel/sys.c b/kernel/sys.c index 04102538cf43f..d06eda1387b69 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1781,7 +1781,9 @@ void getrusage(struct task_struct *p, int who, struct rusage *r) unsigned long maxrss; struct mm_struct *mm; struct signal_struct *sig = p->signal; + unsigned int seq = 0; +retry: memset(r, 0, sizeof(*r)); utime = stime = 0; maxrss = 0; @@ -1793,8 +1795,7 @@ void getrusage(struct task_struct *p, int who, struct rusage *r) goto out_thread; } - if (!lock_task_sighand(p, &flags)) - return; + flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq); switch (who) { case RUSAGE_BOTH: @@ -1822,14 +1823,23 @@ void getrusage(struct task_struct *p, int who, struct rusage *r) r->ru_oublock += sig->oublock; if (maxrss < sig->maxrss) maxrss = sig->maxrss; + + rcu_read_lock(); __for_each_thread(sig, t) accumulate_thread_rusage(t, r); + rcu_read_unlock(); + break; default: BUG(); } - unlock_task_sighand(p, &flags); + + if (need_seqretry(&sig->stats_lock, seq)) { + seq = 1; + goto retry; + } + done_seqretry_irqrestore(&sig->stats_lock, seq, flags); if (who == RUSAGE_CHILDREN) goto out_children; -- 2.43.0