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Date: Sat, 30 Jul 2022 00:29:39 +0200
From: Jan Kara <jack@...e.cz>
To: Khazhismel Kumykov <khazhy@...omium.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Khazhismel Kumykov <khazhy@...gle.com>
Subject: Re: [PATCH] writeback: check wb shutdown for bw_dwork
On Fri 29-07-22 14:51:23, Khazhismel Kumykov wrote:
> This fixes a KASAN splat in timer interrupt after removing a device
>
> Move wb->work_lock to be irq-safe, as complete may be called from irq
>
> Fixes: 45a2966fd641 ("writeback: fix bandwidth estimate for spiky workload")
> Signed-off-by: Khazhismel Kumykov <khazhy@...gle.com>
The patch looks good but I wish there are more details in the changelog
because with this terse changelog I can only guess. I suppose something
like:
writeback: avoid use after free after removing a device
When a disk is removed, bdi_unregister() gets called to stop any further
writeback and wait for the running one to complete. However while IO
completes, wb_inode_writeback_end() will schedule another delayed writeback
and by the time timer fires the bdi_writeback structure may be already
freed. Fix the problem by checking whether bdi is still alive before
scheduling new work in wb_inode_writeback_end(). Since this requires
wb->work_lock and wb_inode_writeback_end() may get called from an
interrupt, switch wb->work_lock to an irqsafe lock.
Honza
> ---
> fs/fs-writeback.c | 12 ++++++------
> mm/backing-dev.c | 10 +++++-----
> mm/page-writeback.c | 6 +++++-
> 3 files changed, 16 insertions(+), 12 deletions(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 05221366a16d..08a1993ab7fd 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -134,10 +134,10 @@ static bool inode_io_list_move_locked(struct inode *inode,
>
> 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_writeback *wb,
> 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_writeback *wb,
> } else
> finish_writeback_work(wb, work);
>
> - spin_unlock_bh(&wb->work_lock);
> + spin_unlock_irq(&wb->work_lock);
> }
>
> /**
> @@ -2082,13 +2082,13 @@ static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
> {
> 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;
> }
>
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index 95550b8fa7fe..de65cb1e5f76 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -260,10 +260,10 @@ void wb_wakeup_delayed(struct bdi_writeback *wb)
> 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)
> @@ -334,12 +334,12 @@ static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb);
> 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);
> /*
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 55c2776ae699..3c34db15cf70 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2867,6 +2867,7 @@ static void wb_inode_writeback_start(struct bdi_writeback *wb)
>
> 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
> @@ -2875,7 +2876,10 @@ static void wb_inode_writeback_end(struct bdi_writeback *wb)
> * 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);
> }
>
> bool __folio_end_writeback(struct folio *folio)
> --
> 2.37.1.455.g008518b4e5-goog
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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