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[140.211.169.12]) by mx.google.com with ESMTPS id f17si30863146pff.171.2019.01.29.16.56.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 29 Jan 2019 16:56:37 -0800 (PST) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) client-ip=140.211.169.12; Authentication-Results: mx.google.com; spf=pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 38E1D359D; Wed, 30 Jan 2019 00:56:37 +0000 (UTC) Date: Tue, 29 Jan 2019 16:56:36 -0800 From: Andrew Morton To: Jan Kara Cc: Al Viro , , Subject: Re: [PATCH] vfs: Avoid softlockups in drop_pagecache_sb() Message-Id: <20190129165636.34a1dc779efdbb9eff4bcf8b@linux-foundation.org> In-Reply-To: <20190114085343.15011-1-jack@suse.cz> References: <20190114085343.15011-1-jack@suse.cz> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 14 Jan 2019 09:53:43 +0100 Jan Kara wrote: > When superblock has lots of inodes without any pagecache (like is the > case for /proc), drop_pagecache_sb() will iterate through all of them > without dropping sb->s_inode_list_lock which can lead to softlockups > (one of our customers hit this). > > Fix the problem by going to the slow path and doing cond_resched() in > case the process needs rescheduling. > > ... > > --- a/fs/drop_caches.c > +++ b/fs/drop_caches.c > @@ -21,8 +21,13 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused) > spin_lock(&sb->s_inode_list_lock); > list_for_each_entry(inode, &sb->s_inodes, i_sb_list) { > spin_lock(&inode->i_lock); > + /* > + * We must skip inodes in unusual state. We may also skip > + * inodes without pages but we deliberately won't in case > + * we need to reschedule to avoid softlockups. > + */ > if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) || > - (inode->i_mapping->nrpages == 0)) { > + (inode->i_mapping->nrpages == 0 && !need_resched())) { > spin_unlock(&inode->i_lock); > continue; > } > @@ -30,6 +35,7 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused) > spin_unlock(&inode->i_lock); > spin_unlock(&sb->s_inode_list_lock); > > + cond_resched(); > invalidate_mapping_pages(inode->i_mapping, 0, -1); > iput(toput_inode); > toput_inode = inode; Are we sure there's no situation in which a large number of inodes can be in the "unusual state", leading to the same issue?