When dev-replace and scrub are run at the same time, dev-replace can be
canceled by scrub. It's quite common for btrfs/069.
The backtrace would be like:
general protection fault: 0000 [#1] SMP
Workqueue: btrfs-endio-raid56 btrfs_endio_raid56_helper [btrfs]
RIP: 0010:[<ffffffff813a2fa8>] [<ffffffff813a2fa8>] generic_make_request_checks+0x198/0x5a0
Call Trace:
[<ffffffff813a4cff>] ? generic_make_request+0xcf/0x290
[<ffffffff813a4c54>] generic_make_request+0x24/0x290
[<ffffffff813a4cff>] ? generic_make_request+0xcf/0x290
[<ffffffff813a4f2e>] submit_bio+0x6e/0x120
[<ffffffffa087279d>] ? page_in_rbio+0x4d/0x80 [btrfs]
[<ffffffffa08737d0>] ? rbio_orig_end_io+0x80/0x80 [btrfs]
[<ffffffffa0873e31>] finish_rmw+0x401/0x550 [btrfs]
[<ffffffffa0874fc6>] validate_rbio_for_rmw+0x36/0x40 [btrfs]
[<ffffffffa087504d>] raid_rmw_end_io+0x7d/0x90 [btrfs]
[<ffffffff8139c536>] bio_endio+0x56/0x60
[<ffffffffa07e6e5c>] end_workqueue_fn+0x3c/0x40 [btrfs]
[<ffffffffa08285bf>] btrfs_scrubparity_helper+0xef/0x610 [btrfs]
[<ffffffffa0828b9e>] btrfs_endio_raid56_helper+0xe/0x10 [btrfs]
[<ffffffff810ec8df>] process_one_work+0x2af/0x720
[<ffffffff810ec85b>] ? process_one_work+0x22b/0x720
[<ffffffff810ecd9b>] worker_thread+0x4b/0x4f0
[<ffffffff810ecd50>] ? process_one_work+0x720/0x720
[<ffffffff810ecd50>] ? process_one_work+0x720/0x720
[<ffffffff810f39d3>] kthread+0xf3/0x110
[<ffffffff810f38e0>] ? kthread_park+0x60/0x60
[<ffffffff81857647>] ret_from_fork+0x27/0x40
While in that case, target device can be destroyed at cancel time,
leading to a user-after-free bug:
Process A (dev-replace) | Process B(scrub)
----------------------------------------------------------------------
|(Any RW is OK)
|scrub_setup_recheck_block()
||- btrfs_map_sblock()
| Got a bbio with tgtdev
btrfs_dev_replace_finishing() |
|- btrfs_destory_dev_replace_tgtdev()|
|- call_rcu(free_device) |
|- __free_device() |
|- kfree(device) |
| Scrub worker:
| Access bbio->stripes[], which
| contains tgtdev.
| This triggers general protection.
The bug is mostly obvious for RAID5/6 since raid56 choose to keep old
rbio and rbio->bbio for later steal, this hugely enlarged the race
window and makes it much easier to trigger the bug.
This patch introduces 'tgtdev_refs' and 'tgtdev_wait' for btrfs_device
to wait for all its user released the target device.
Signed-off-by: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
---
fs/btrfs/dev-replace.c | 7 ++++++-
fs/btrfs/volumes.c | 36 +++++++++++++++++++++++++++++++++++-
fs/btrfs/volumes.h | 10 ++++++++++
3 files changed, 51 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 5de280b9ad73..794a6a0bedf2 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -558,7 +558,6 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
rcu_str_deref(src_device->name),
src_device->devid,
rcu_str_deref(tgt_device->name));
- tgt_device->is_tgtdev_for_dev_replace = 0;
tgt_device->devid = src_device->devid;
src_device->devid = BTRFS_DEV_REPLACE_DEVID;
memcpy(uuid_tmp, tgt_device->uuid, sizeof(uuid_tmp));
@@ -579,6 +578,12 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
btrfs_dev_replace_unlock(dev_replace, 1);
+ /*
+ * Only change is_tgtdev_for_dev_replace flag after all its
+ * users get released.
+ */
+ wait_target_device(tgt_device);
+ tgt_device->is_tgtdev_for_dev_replace = 0;
btrfs_rm_dev_replace_blocked(fs_info);
btrfs_rm_dev_replace_remove_srcdev(fs_info, src_device);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 3c3c69c0eee4..84db9fb22b7d 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2064,6 +2064,7 @@ void btrfs_destroy_dev_replace_tgtdev(struct btrfs_fs_info *fs_info,
WARN_ON(!tgtdev);
mutex_lock(&fs_info->fs_devices->device_list_mutex);
+ wait_target_device(tgtdev);
btrfs_sysfs_rm_device_link(fs_info->fs_devices, tgtdev);
if (tgtdev->bdev)
@@ -2598,6 +2599,8 @@ int btrfs_init_dev_replace_tgtdev(struct btrfs_fs_info *fs_info,
device->is_tgtdev_for_dev_replace = 1;
device->mode = FMODE_EXCL;
device->dev_stats_valid = 1;
+ atomic_set(&device->tgtdev_refs, 0);
+ init_waitqueue_head(&device->tgtdev_wait);
set_blocksize(device->bdev, 4096);
device->fs_devices = fs_info->fs_devices;
list_add(&device->dev_list, &fs_info->fs_devices->devices);
@@ -2624,6 +2627,8 @@ void btrfs_init_dev_replace_tgtdev_for_resume(struct btrfs_fs_info *fs_info,
tgtdev->sector_size = sectorsize;
tgtdev->fs_info = fs_info;
tgtdev->in_fs_metadata = 1;
+ atomic_set(&tgtdev->tgtdev_refs, 0);
+ init_waitqueue_head(&tgtdev->tgtdev_wait);
}
static noinline int btrfs_update_device(struct btrfs_trans_handle *trans,
@@ -5302,6 +5307,32 @@ static struct btrfs_bio *alloc_btrfs_bio(int total_stripes, int real_stripes)
return bbio;
}
+static void pin_bbio_target_device(struct btrfs_bio *bbio)
+{
+ int i;
+
+ for (i = 0; i < bbio->num_stripes; i++) {
+ struct btrfs_device *device = bbio->stripes[i].dev;
+
+ if (device->is_tgtdev_for_dev_replace)
+ atomic_inc(&device->tgtdev_refs);
+ }
+}
+
+static void unpin_bbio_target_device(struct btrfs_bio *bbio)
+{
+ int i;
+
+ for (i = 0; i < bbio->num_stripes; i++) {
+ struct btrfs_device *device = bbio->stripes[i].dev;
+
+ if (device->is_tgtdev_for_dev_replace) {
+ atomic_dec(&device->tgtdev_refs);
+ wake_up(&device->tgtdev_wait);
+ }
+ }
+}
+
void btrfs_get_bbio(struct btrfs_bio *bbio)
{
WARN_ON(!atomic_read(&bbio->refs));
@@ -5312,8 +5343,10 @@ void btrfs_put_bbio(struct btrfs_bio *bbio)
{
if (!bbio)
return;
- if (atomic_dec_and_test(&bbio->refs))
+ if (atomic_dec_and_test(&bbio->refs)) {
+ unpin_bbio_target_device(bbio);
kfree(bbio);
+ }
}
static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
@@ -5868,6 +5901,7 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
bbio->stripes[0].physical = physical_to_patch_in_first_stripe;
bbio->mirror_num = map->num_stripes + 1;
}
+ pin_bbio_target_device(bbio);
out:
if (dev_replace_is_ongoing) {
btrfs_dev_replace_clear_lock_blocking(dev_replace);
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 24ba6bc3ec34..702361182597 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -149,6 +149,10 @@ struct btrfs_device {
/* Counter to record the change of device stats */
atomic_t dev_stats_ccnt;
atomic_t dev_stat_values[BTRFS_DEV_STAT_VALUES_MAX];
+
+ /* To ensure we wait this target device before destroying it */
+ atomic_t tgtdev_refs;
+ wait_queue_head_t tgtdev_wait;
};
/*
@@ -538,4 +542,10 @@ struct list_head *btrfs_get_fs_uuids(void);
void btrfs_set_fs_info_ptr(struct btrfs_fs_info *fs_info);
void btrfs_reset_fs_info_ptr(struct btrfs_fs_info *fs_info);
+static inline void wait_target_device(struct btrfs_device *tgtdev)
+{
+ if (!tgtdev || !tgtdev->is_tgtdev_for_dev_replace)
+ return;
+ wait_event(tgtdev->tgtdev_wait, atomic_read(&tgtdev->tgtdev_refs) == 0);
+}
#endif
--
2.11.0
--
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