Re: [PATCH] block: fix deadlock between bd_link_disk_holder and partition scan

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi, Christoph

在 2024/02/07 17:27, linan666@xxxxxxxxxxxxxxx 写道:
From: Li Nan <linan122@xxxxxxxxxx>

'open_mutex' of gendisk is used to protect open/close block devices. But
in bd_link_disk_holder(), it is used to protect the creation of symlink
between holding disk and slave bdev, which introduces some issues.

When bd_link_disk_holder() is called, the driver is usually in the process
of initialization/modification and may suspend submitting io. At this
time, any io hold 'open_mutex', such as scanning partitions, can cause
deadlocks. For example, in raid:

T1                              T2
bdev_open_by_dev
  lock open_mutex [1]
  ...
   efi_partition
   ...
    md_submit_bio
				md_ioctl mddev_syspend
				  -> suspend all io
				 md_add_new_disk
				  bind_rdev_to_array
				   bd_link_disk_holder
				    try lock open_mutex [2]
     md_handle_request
      -> wait mddev_resume

T1 scan partition, T2 add a new device to raid. T1 waits for T2 to resume
mddev, but T2 waits for open_mutex held by T1. Deadlock occurs.

Fix it by introducing a local mutex 'holder_mutex' to replace 'open_mutex'.

Can you take a look at this patch? I think for raid(perhaps and dm and
other drivers), it's reasonable to suspend IO while hot adding new
underlying disks. And I think add new slaves to holder is not related to
open the holder disk, because caller should already open the holder disk
to hot add slaves, hence 'open_mutex' for holder is not necessary here.

Actually bd_link_disk_holder() is protected by 'reconfig_mutex' for
raid, and 'table_devices_lock' for dm(I'm not sure yet if other drivers
have similiar lock).

For raid, we do can fix this problem in raid by delay
bd_link_disk_holder() while the array is not suspended, however, we'll
consider this fix later if you think this patch is not acceptable.

Thanks,
Kuai


Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
---
  block/holder.c | 12 +++++++-----
  1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/block/holder.c b/block/holder.c
index 37d18c13d958..5bfb0a674cc7 100644
--- a/block/holder.c
+++ b/block/holder.c
@@ -8,6 +8,8 @@ struct bd_holder_disk {
  	int			refcnt;
  };
+static DEFINE_MUTEX(holder_mutex);
+
  static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
  						  struct gendisk *disk)
  {
@@ -80,7 +82,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
  	kobject_get(bdev->bd_holder_dir);
  	mutex_unlock(&bdev->bd_disk->open_mutex);
- mutex_lock(&disk->open_mutex);
+	mutex_lock(&holder_mutex);
  	WARN_ON_ONCE(!bdev->bd_holder);
holder = bd_find_holder_disk(bdev, disk);
@@ -108,7 +110,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
  		goto out_del_symlink;
  	list_add(&holder->list, &disk->slave_bdevs);
- mutex_unlock(&disk->open_mutex);
+	mutex_unlock(&holder_mutex);
  	return 0;
out_del_symlink:
@@ -116,7 +118,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
  out_free_holder:
  	kfree(holder);
  out_unlock:
-	mutex_unlock(&disk->open_mutex);
+	mutex_unlock(&holder_mutex);
  	if (ret)
  		kobject_put(bdev->bd_holder_dir);
  	return ret;
@@ -140,7 +142,7 @@ void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
  	if (WARN_ON_ONCE(!disk->slave_dir))
  		return;
- mutex_lock(&disk->open_mutex);
+	mutex_lock(&holder_mutex);
  	holder = bd_find_holder_disk(bdev, disk);
  	if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
  		del_symlink(disk->slave_dir, bdev_kobj(bdev));
@@ -149,6 +151,6 @@ void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
  		list_del_init(&holder->list);
  		kfree(holder);
  	}
-	mutex_unlock(&disk->open_mutex);
+	mutex_unlock(&holder_mutex);
  }
  EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);






[Index of Archives]     [Linux RAID]     [Linux SCSI]     [Linux ATA RAID]     [IDE]     [Linux Wireless]     [Linux Kernel]     [ATH6KL]     [Linux Bluetooth]     [Linux Netdev]     [Kernel Newbies]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Device Mapper]

  Powered by Linux