blk-cgroup: be able to remove the record of unplugged device

The bug is we're not able to remove the device from blkio cgroup's
per-device control files if it gets unplugged.

To reproduce the bug:

  # mount -t cgroup -o blkio xxx /cgroup
  # cd /cgroup
  # echo "8:0 1000" > blkio.throttle.read_bps_device
  # unplug the device
  # cat blkio.throttle.read_bps_device
  8:0	1000
  # echo "8:0 0" > blkio.throttle.read_bps_device
  -bash: echo: write error: No such device

After patching, the device removal will succeed.

Thanks for the comments of Paul, Zefan, and Vivek.

Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <paul@paulmenage.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 16 insertions, 21 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index bcaf16ee6ad1..b596e54ddd71 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -785,10 +785,10 @@ static int blkio_policy_parse_and_set(char *buf,
 {
         char *s[4], *p, *major_s = NULL, *minor_s = NULL;
         int ret;
-        unsigned long major, minor, temp;
+        unsigned long major, minor;
         int i = 0;
         dev_t dev;
-        u64 bps, iops;
+        u64 temp;
 
         memset(s, 0, sizeof(s));
 
@@ -826,20 +826,23 @@ static int blkio_policy_parse_and_set(char *buf,
 
         dev = MKDEV(major, minor);
 
-        ret = blkio_check_dev_num(dev);
+        ret = strict_strtoull(s[1], 10, &temp);
         if (ret)
-                return ret;
+                return -EINVAL;
 
-        newpn->dev = dev;
+        /* For rule removal, do not check for device presence. */
+        if (temp) {
+                ret = blkio_check_dev_num(dev);
+                if (ret)
+                        return ret;
+        }
 
-        if (s[1] == NULL)
-                return -EINVAL;
+        newpn->dev = dev;
 
         switch (plid) {
         case BLKIO_POLICY_PROP:
-                ret = strict_strtoul(s[1], 10, &temp);
-                if (ret || (temp < BLKIO_WEIGHT_MIN && temp > 0) ||
-                        temp > BLKIO_WEIGHT_MAX)
+                if ((temp < BLKIO_WEIGHT_MIN && temp > 0) ||
+                     temp > BLKIO_WEIGHT_MAX)
                         return -EINVAL;
 
                 newpn->plid = plid;
@@ -850,26 +853,18 @@ static int blkio_policy_parse_and_set(char *buf,
                 switch(fileid) {
                 case BLKIO_THROTL_read_bps_device:
                 case BLKIO_THROTL_write_bps_device:
-                        ret = strict_strtoull(s[1], 10, &bps);
-                        if (ret)
-                                return -EINVAL;
-
                         newpn->plid = plid;
                         newpn->fileid = fileid;
-                        newpn->val.bps = bps;
+                        newpn->val.bps = temp;
                         break;
                 case BLKIO_THROTL_read_iops_device:
                 case BLKIO_THROTL_write_iops_device:
-                        ret = strict_strtoull(s[1], 10, &iops);
-                        if (ret)
-                                return -EINVAL;
-
-                        if (iops > THROTL_IOPS_MAX)
+                        if (temp > THROTL_IOPS_MAX)
                                 return -EINVAL;
 
                         newpn->plid = plid;
                         newpn->fileid = fileid;
-                        newpn->val.iops = (unsigned int)iops;
+                        newpn->val.iops = (unsigned int)temp;
                         break;
                 }
                 break;