[PATCH 5.15 105/136] writeback: avoid use-after-free after removing device

Greg Kroah-Hartman
2022-08-29T11:31:34Z

From: Khazhismel Kumykov <khazhy@chromium.org>

commit f87904c075515f3e1d8f4a7115869d3b914674fd upstream.

When a disk is removed, bdi_unregister gets called to stop further
writeback and wait for associated delayed work to complete. However,
wb_inode_writeback_end() may schedule bandwidth estimation dwork after
this has completed, which can result in the timer attempting to access the
just freed bdi_writeback.

Fix this by checking if the bdi_writeback is alive, similar to when
scheduling writeback work.

Since this requires wb->work_lock, and wb_inode_writeback_end() may get
called from interrupt, switch wb->work_lock to an irqsafe lock.

Link: https://lkml.kernel.org/r/20220801155034.3772543-1-khazhy@google.com
Fixes: 45a2966fd641 ("writeback: fix bandwidth estimate for spiky workload")
Signed-off-by: Khazhismel Kumykov <khazhy@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Michael Stapelberg <stapelberg+linux@google.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/fs-writeback.c | 12 ++++++------
mm/backing-dev.c | 10 +++++-----
mm/page-writeback.c | 6 +++++-
3 files changed, 16 insertions(+), 12 deletions(-)

--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -134,10 +134,10 @@ static bool inode_io_list_move_locked(st

static void wb_wakeup(struct bdi_writeback *wb)
{
- spin_lock_bh(&wb->work_lock);
+ spin_lock_irq(&wb->work_lock);
if (test_bit(WB_registered, &wb->state))
mod_delayed_work(bdi_wq, &wb->dwork, 0);
- spin_unlock_bh(&wb->work_lock);
+ spin_unlock_irq(&wb->work_lock);
}

static void finish_writeback_work(struct bdi_writeback *wb,
@@ -164,7 +164,7 @@ static void wb_queue_work(struct bdi_wri
if (work->done)
atomic_inc(&work->done->cnt);

- spin_lock_bh(&wb->work_lock);
+ spin_lock_irq(&wb->work_lock);

if (test_bit(WB_registered, &wb->state)) {
list_add_tail(&work->list, &wb->work_list);
@@ -172,7 +172,7 @@ static void wb_queue_work(struct bdi_wri
} else
finish_writeback_work(wb, work);

- spin_unlock_bh(&wb->work_lock);
+ spin_unlock_irq(&wb->work_lock);
}

/**
@@ -2109,13 +2109,13 @@ static struct wb_writeback_work *get_nex
{
struct wb_writeback_work *work = NULL;

- spin_lock_bh(&wb->work_lock);
+ spin_lock_irq(&wb->work_lock);
if (!list_empty(&wb->work_list)) {
work = list_entry(wb->work_list.next,
struct wb_writeback_work, list);
list_del_init(&work->list);
}
- spin_unlock_bh(&wb->work_lock);
+ spin_unlock_irq(&wb->work_lock);
return work;
}

--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -258,10 +258,10 @@ void wb_wakeup_delayed(struct bdi_writeb
unsigned long timeout;

timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
- spin_lock_bh(&wb->work_lock);
+ spin_lock_irq(&wb->work_lock);
if (test_bit(WB_registered, &wb->state))
queue_delayed_work(bdi_wq, &wb->dwork, timeout);
- spin_unlock_bh(&wb->work_lock);
+ spin_unlock_irq(&wb->work_lock);
}

static void wb_update_bandwidth_workfn(struct work_struct *work)
@@ -337,12 +337,12 @@ static void cgwb_remove_from_bdi_list(st
static void wb_shutdown(struct bdi_writeback *wb)
{
/* Make sure nobody queues further work */
- spin_lock_bh(&wb->work_lock);
+ spin_lock_irq(&wb->work_lock);
if (!test_and_clear_bit(WB_registered, &wb->state)) {
- spin_unlock_bh(&wb->work_lock);
+ spin_unlock_irq(&wb->work_lock);
return;
}
- spin_unlock_bh(&wb->work_lock);
+ spin_unlock_irq(&wb->work_lock);

cgwb_remove_from_bdi_list(wb);
/*
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2755,6 +2755,7 @@ static void wb_inode_writeback_start(str

static void wb_inode_writeback_end(struct bdi_writeback *wb)
{
+ unsigned long flags;
atomic_dec(&wb->writeback_inodes);
/*
* Make sure estimate of writeback throughput gets updated after
@@ -2763,7 +2764,10 @@ static void wb_inode_writeback_end(struc
* that if multiple inodes end writeback at a similar time, they get
* batched into one bandwidth update.
*/
- queue_delayed_work(bdi_wq, &wb->bw_dwork, BANDWIDTH_INTERVAL);
+ spin_lock_irqsave(&wb->work_lock, flags);
+ if (test_bit(WB_registered, &wb->state))
+ queue_delayed_work(bdi_wq, &wb->bw_dwork, BANDWIDTH_INTERVAL);
+ spin_unlock_irqrestore(&wb->work_lock, flags);
}

int test_clear_page_writeback(struct page *page)