The patch titled
Subject: writeback: avoid use-after-free after removing device
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
writeback-avoid-use-after-free-after-removing-device.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/writeback-avoid-use-after-free-after-removing-device.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Khazhismel Kumykov <khazhy@xxxxxxxxxxxx>
Subject: writeback: avoid use-after-free after removing device
Date: Mon, 1 Aug 2022 08:50:34 -0700
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@xxxxxxxxxx
Fixes: 45a2966fd641 ("writeback: fix bandwidth estimate for spiky workload")
Signed-off-by: Khazhismel Kumykov <khazhy@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Michael Stapelberg <stapelberg+linux@xxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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~writeback-avoid-use-after-free-after-removing-device
+++ a/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);
}
/**
@@ -2082,13 +2082,13 @@ 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~writeback-avoid-use-after-free-after-removing-device
+++ a/mm/backing-dev.c
@@ -260,10 +260,10 @@ 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)
@@ -334,12 +334,12 @@ 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~writeback-avoid-use-after-free-after-removing-device
+++ a/mm/page-writeback.c
@@ -2867,6 +2867,7 @@ 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
@@ -2875,7 +2876,10 @@ 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);
}
bool __folio_end_writeback(struct folio *folio)
_
Patches currently in -mm which might be from khazhy@xxxxxxxxxxxx are
writeback-avoid-use-after-free-after-removing-device.patch
