From 669420644c79c207f83fdf9105ae782867e2991f Mon Sep 17 00:00:00 2001 From: Alex Chiang Date: Fri, 13 Mar 2009 12:07:36 -0600 Subject: 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 Acked-by: Cornelia Huck Signed-off-by: Greg Kroah-Hartman --- drivers/s390/cio/ccwgroup.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'drivers/s390/cio/ccwgroup.c') 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; -- cgit v1.2.3