git: sys/dev/disk/dm: Fix race on pdev create

[Tomohiro Kusumi]

commit ac816675c8321309b49d6a335f95c5388036803f
Author: Tomohiro Kusumi <kusumi.tomohiro at gmail.com>
Date:   Mon Oct 12 12:07:31 2015 +0900

    sys/dev/disk/dm: Fix race on pdev create
    
    List lookup and insert need to be atomic otherwise more than
    one dm_pdev_t* for the same underlying device could exist.
    Running the following two concurrently reproduces the race
    where ${DEV} is the common underlying device.
    
    =====(A)
      #!/usr/local/bin/bash
      kldload dm_target_linear
      while [ 1 ]; do
      	dmsetup create linear1 --table "0 1000 linear ${DEV} 0"
      	dmsetup remove /dev/mapper/linear1
      done
    
    =====(B)
      #!/usr/local/bin/bash
      kldload dm_target_delay
      while [ 1 ]; do
      	dmsetup create delay1 --table "0 1000 delay ${DEV} 0 10"
      	dmsetup remove /dev/mapper/delay1
      done

Summary of changes:
 sys/dev/disk/dm/dm_pdev.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/ac816675c8321309b49d6a335f95c5388036803f


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