在 2024/2/8 14:50, Song Liu 写道:

On Wed, Feb 7, 2024 at 1:32 AM [off-list ref] wrote:

quoted

From: Li Nan <redacted>

'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'.

Is this to fix [1]? Do we need some Fixes and/or Closes tags?

No. Just use another way to fix [2], and both [2] and this patch can fix
the issue. I am not sure about the root cause of [1] yet.

[2] https://patchwork.kernel.org/project/linux-raid/list/?series=812045

Could you please add steps to reproduce this issue?

We need to modify the kernel, add sleep in md_submit_bio() and md_ioctl()
as below, and then:
   1. mdadm -CR /dev/md0 -l1 -n2 /dev/sd[bc]  #create a raid
   2. echo 1 > /sys/module/md_mod/parameters/error_inject  #enable sleep
   3. 'mdadm --add /dev/md0 /dev/sda'  #add a disk to raid
   4. submit ioctl BLKRRPART to raid within 10s.


Changes of kernel:

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 350f5b22ba6f..ce16d319edf2 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c

@@ -76,6 +76,8 @@ static DEFINE_SPINLOCK(pers_lock);

  static const struct kobj_type md_ktype;

+static bool error_inject = false;
+
  struct md_cluster_operations *md_cluster_ops;
  EXPORT_SYMBOL(md_cluster_ops);
  static struct module *md_cluster_mod;

@@ -372,6 +374,8 @@ static bool is_suspended(struct mddev *mddev, struct 

bio *bio)

  void md_handle_request(struct mddev *mddev, struct bio *bio)
  {
+       if (error_inject)
+               ssleep(10);
  check_suspended:
         if (is_suspended(mddev, bio)) {
                 DEFINE_WAIT(__wait);

@@ -7752,6 +7756,8 @@ static int md_ioctl(struct block_device *bdev, 

blk_mode_t mode,
                  */
                 if (mddev->pers) {
                         mdu_disk_info_t info;
+                       if (error_inject)
+                               ssleep(10);
                         if (copy_from_user(&info, argp, sizeof(info)))
                                 err = -EFAULT;
                         else if (!(info.state & (1<<MD_DISK_SYNC)))

@@ -10120,6 +10126,7 @@ module_param_call(start_ro, set_ro, get_ro, NULL, 

S_IRUSR|S_IWUSR);
  module_param(start_dirty_degraded, int, S_IRUGO|S_IWUSR);
  module_param_call(new_array, add_named_array, NULL, NULL, S_IWUSR);
  module_param(create_on_open, bool, S_IRUSR|S_IWUSR);
+module_param(error_inject, bool, S_IRUSR|S_IWUSR);

  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("MD RAID framework");


-- 
Thanks,
Nan