From: Roman Gushchin <guro@fb.com> To: Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org> Cc: <linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>, Alexander Viro <viro@zeniv.linux.org.uk>, Dennis Zhou <dennis@kernel.org>, Dave Chinner <dchinner@redhat.com>, <cgroups@vger.kernel.org>, Roman Gushchin <guro@fb.com>, Jan Kara <jack@suse.com> Subject: [PATCH v8 3/8] writeback, cgroup: increment isw_nr_in_flight before grabbing an inode Date: Mon, 7 Jun 2021 18:31:18 -0700 [thread overview] Message-ID: <20210608013123.1088882-4-guro@fb.com> (raw) In-Reply-To: <20210608013123.1088882-1-guro@fb.com> isw_nr_in_flight is used do determine whether the inode switch queue should be flushed from the umount path. Currently it's increased after grabbing an inode and even scheduling the switch work. It means the umount path can be walked past cleanup_offline_cgwb() with active inode references, which can result in a "Busy inodes after unmount." message and use-after-free issues (with inode->i_sb which gets freed). Fix it by incrementing isw_nr_in_flight before doing anything with the inode and decrementing in the case when switching wasn't scheduled. The problem hasn't yet been seen in the real life and was discovered by Jan Kara by looking into the code. Suggested-by: Jan Kara <jack@suse.com> Signed-off-by: Roman Gushchin <guro@fb.com> --- fs/fs-writeback.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 3564efcc4b78..e2cc860a001b 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -505,6 +505,8 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) if (!isw) return; + atomic_inc(&isw_nr_in_flight); + /* find and pin the new wb */ rcu_read_lock(); memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys); @@ -535,11 +537,10 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) * Let's continue after I_WB_SWITCH is guaranteed to be visible. */ call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn); - - atomic_inc(&isw_nr_in_flight); return; out_free: + atomic_dec(&isw_nr_in_flight); if (isw->new_wb) wb_put(isw->new_wb); kfree(isw); -- 2.31.1
WARNING: multiple messages have this Message-ID (diff)
From: Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org> To: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Cc: linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Alexander Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>, Dennis Zhou <dennis-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Dave Chinner <dchinner-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>, Jan Kara <jack-IBi9RG/b67k@public.gmane.org> Subject: [PATCH v8 3/8] writeback, cgroup: increment isw_nr_in_flight before grabbing an inode Date: Mon, 7 Jun 2021 18:31:18 -0700 [thread overview] Message-ID: <20210608013123.1088882-4-guro@fb.com> (raw) In-Reply-To: <20210608013123.1088882-1-guro-b10kYP2dOMg@public.gmane.org> isw_nr_in_flight is used do determine whether the inode switch queue should be flushed from the umount path. Currently it's increased after grabbing an inode and even scheduling the switch work. It means the umount path can be walked past cleanup_offline_cgwb() with active inode references, which can result in a "Busy inodes after unmount." message and use-after-free issues (with inode->i_sb which gets freed). Fix it by incrementing isw_nr_in_flight before doing anything with the inode and decrementing in the case when switching wasn't scheduled. The problem hasn't yet been seen in the real life and was discovered by Jan Kara by looking into the code. Suggested-by: Jan Kara <jack-IBi9RG/b67k@public.gmane.org> Signed-off-by: Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org> --- fs/fs-writeback.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 3564efcc4b78..e2cc860a001b 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -505,6 +505,8 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) if (!isw) return; + atomic_inc(&isw_nr_in_flight); + /* find and pin the new wb */ rcu_read_lock(); memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys); @@ -535,11 +537,10 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) * Let's continue after I_WB_SWITCH is guaranteed to be visible. */ call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn); - - atomic_inc(&isw_nr_in_flight); return; out_free: + atomic_dec(&isw_nr_in_flight); if (isw->new_wb) wb_put(isw->new_wb); kfree(isw); -- 2.31.1
next prev parent reply other threads:[~2021-06-08 1:34 UTC|newest] Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-08 1:31 [PATCH v8 0/8] cgroup, blkcg: prevent dirty inodes to pin dying memory cgroups Roman Gushchin 2021-06-08 1:31 ` Roman Gushchin 2021-06-08 1:31 ` [PATCH v8 1/8] writeback, cgroup: do not switch inodes with I_WILL_FREE flag Roman Gushchin 2021-06-08 1:31 ` Roman Gushchin 2021-06-08 1:31 ` [PATCH v8 2/8] writeback, cgroup: add smp_mb() to cgroup_writeback_umount() Roman Gushchin 2021-06-08 1:31 ` Roman Gushchin 2021-06-08 8:43 ` Jan Kara 2021-06-08 1:31 ` Roman Gushchin [this message] 2021-06-08 1:31 ` [PATCH v8 3/8] writeback, cgroup: increment isw_nr_in_flight before grabbing an inode Roman Gushchin 2021-06-08 8:45 ` Jan Kara 2021-06-08 8:45 ` Jan Kara 2021-06-08 1:31 ` [PATCH v8 4/8] writeback, cgroup: switch to rcu_work API in inode_switch_wbs() Roman Gushchin 2021-06-08 1:31 ` Roman Gushchin 2021-06-08 1:31 ` [PATCH v8 5/8] writeback, cgroup: keep list of inodes attached to bdi_writeback Roman Gushchin 2021-06-08 1:31 ` Roman Gushchin 2021-06-08 1:31 ` [PATCH v8 6/8] writeback, cgroup: split out the functional part of inode_switch_wbs_work_fn() Roman Gushchin 2021-06-08 1:31 ` Roman Gushchin 2021-06-08 1:31 ` [PATCH v8 7/8] writeback, cgroup: support switching multiple inodes at once Roman Gushchin 2021-06-08 1:31 ` Roman Gushchin 2021-06-08 1:31 ` [PATCH v8 8/8] writeback, cgroup: release dying cgwbs by switching attached inodes Roman Gushchin 2021-06-08 1:31 ` Roman Gushchin 2021-06-08 8:54 ` Jan Kara 2021-06-08 16:08 ` Dennis Zhou 2021-06-08 16:08 ` Dennis Zhou 2021-06-08 22:37 ` Roman Gushchin 2021-06-08 22:37 ` Roman Gushchin
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