From 5ff8eaac1636bf6deae86491f4818c4c69d1a9ac Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 16 Feb 2016 11:34:07 -0700 Subject: [PATCH] writeback: keep superblock pinned during cgroup writeback association switches If cgroup writeback is in use, an inode is associated with a cgroup for writeback. If the inode's main dirtier changes to another cgroup, the association gets updated asynchronously. Nothing was pinning the superblock while such switches are in progress and superblock could go away while async switching is pending or in progress leading to crashes like the following. kernel BUG at fs/jbd2/transaction.c:319! invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC CPU: 1 PID: 29158 Comm: kworker/1:10 Not tainted 4.5.0-rc3 #51 Hardware name: Google Google, BIOS Google 01/01/2011 Workqueue: events inode_switch_wbs_work_fn task: ffff880213dbbd40 ti: ffff880209264000 task.ti: ffff880209264000 RIP: 0010:[] [] start_this_handle+0x382/0x3e0 RSP: 0018:ffff880209267c30 EFLAGS: 00010202 ... Call Trace: [] jbd2__journal_start+0xf4/0x190 [] __ext4_journal_start_sb+0x4e/0x70 [] ext4_evict_inode+0x12c/0x3d0 [] evict+0xbb/0x190 [] iput+0x130/0x190 [] inode_switch_wbs_work_fn+0x343/0x4c0 [] process_one_work+0x129/0x300 [] worker_thread+0x126/0x480 [] kthread+0xc4/0xe0 [] ret_from_fork+0x3f/0x70 Fix it by bumping s_active while cgroup association switching is in flight. Signed-off-by: Tejun Heo Reported-and-tested-by: Tahsin Erdogan Link: http://lkml.kernel.org/g/CAAeU0aNCq7LGODvVGRU-oU_o-6enii5ey0p1c26D1ZzYwkDc5A@mail.gmail.com Fixes: d10c80955265 ("writeback: implement foreign cgroup inode bdi_writeback switching") Cc: stable@vger.kernel.org #v4.5+ Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 6915c950e6e8..1f76d8950a57 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -317,6 +317,7 @@ static void inode_switch_wbs_work_fn(struct work_struct *work) struct inode_switch_wbs_context *isw = container_of(work, struct inode_switch_wbs_context, work); struct inode *inode = isw->inode; + struct super_block *sb = inode->i_sb; struct address_space *mapping = inode->i_mapping; struct bdi_writeback *old_wb = inode->i_wb; struct bdi_writeback *new_wb = isw->new_wb; @@ -423,6 +424,7 @@ skip_switch: wb_put(new_wb); iput(inode); + deactivate_super(sb); kfree(isw); } @@ -469,11 +471,14 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) /* while holding I_WB_SWITCH, no one else can update the association */ spin_lock(&inode->i_lock); + if (inode->i_state & (I_WB_SWITCH | I_FREEING) || - inode_to_wb(inode) == isw->new_wb) { - spin_unlock(&inode->i_lock); - goto out_free; - } + inode_to_wb(inode) == isw->new_wb) + goto out_unlock; + + if (!atomic_inc_not_zero(&inode->i_sb->s_active)) + goto out_unlock; + inode->i_state |= I_WB_SWITCH; spin_unlock(&inode->i_lock); @@ -489,6 +494,8 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn); return; +out_unlock: + spin_unlock(&inode->i_lock); out_free: if (isw->new_wb) wb_put(isw->new_wb); -- 2.20.1