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authorAlex Chiang <achiang@hp.com>2009-03-13 12:07:36 -0600
committerGreg Kroah-Hartman <gregkh@suse.de>2009-03-24 16:38:26 -0700
commit669420644c79c207f83fdf9105ae782867e2991f (patch)
tree668491b3700bcc65e45d5ff9471f6fde5d5743af /drivers/s390/cio
parentffa6a7054d172a2f57248dff2de600ca795c5656 (diff)
sysfs: only allow one scheduled removal callback per kobj
The only way for a sysfs attribute to remove itself (without deadlock) is to use the sysfs_schedule_callback() interface. Vegard Nossum discovered that a poorly written sysfs ->store callback can repeatedly schedule remove callbacks on the same device over and over, e.g. $ while true ; do echo 1 > /sys/devices/.../remove ; done If the 'remove' attribute uses the sysfs_schedule_callback API and also does not protect itself from concurrent accesses, its callback handler will be called multiple times, and will eventually attempt to perform operations on a freed kobject, leading to many problems. Instead of requiring all callers of sysfs_schedule_callback to implement their own synchronization, provide the protection in the infrastructure. Now, sysfs_schedule_callback will only allow one scheduled callback per kobject. On subsequent calls with the same kobject, return -EAGAIN. This is a short term fix. The long term fix is to allow sysfs attributes to remove themselves directly, without any of this callback hokey pokey. [cornelia.huck@de.ibm.com: s390 ccwgroup bits] Reported-by: vegard.nossum@gmail.com Signed-off-by: Alex Chiang <achiang@hp.com> Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'drivers/s390/cio')
-rw-r--r--drivers/s390/cio/ccwgroup.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/drivers/s390/cio/ccwgroup.c b/drivers/s390/cio/ccwgroup.c
index 918e6fce257..b91c1719b07 100644
--- a/drivers/s390/cio/ccwgroup.c
+++ b/drivers/s390/cio/ccwgroup.c
@@ -104,8 +104,9 @@ ccwgroup_ungroup_store(struct device *dev, struct device_attribute *attr, const
rc = device_schedule_callback(dev, ccwgroup_ungroup_callback);
out:
if (rc) {
- /* Release onoff "lock" when ungrouping failed. */
- atomic_set(&gdev->onoff, 0);
+ if (rc != -EAGAIN)
+ /* Release onoff "lock" when ungrouping failed. */
+ atomic_set(&gdev->onoff, 0);
return rc;
}
return count;