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authorOliver Neukum <oneukum@suse.com>2016-01-21 15:18:48 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-02-03 13:29:12 -0800
commitb4a90d04ac79349799f65dfd7fa30b2aac6b2a4d (patch)
tree118b7d516443bbd7e265d2d20162c7e55ed8f232 /drivers/usb/core
parent7dd9cba5bb90ffa9c60c1533b715dc91c5082cd9 (diff)
usb: no locking for reading descriptors in sysfs
Quting the relevant thread: > In fact, I suspect the locking added by the kernel 3.13 commit for > read_descriptors() is invalid because read_descriptors() performs no USB > activity; read_descriptors() just reads information from an allocated > memory structure. This structure is protected as the structure is > existing before and after the sysfs vfs descriptors entry is created or > destroyed. You're right. For some reason I thought that usb_deauthorize_device() would destroy the rawdescriptor structures (as mentioned in that commit's Changelog), but it doesn't. The locking in read_descriptors() is unnecessary. > The information is only written at the time of enumeration > and does not change. At least that is my understanding. > > It is noted that in our testing of kernel 3.8 on ARM, that sysfs > read_descriptors() was non-blocking because the kernel 3.13 comment was > not there. > > The pre-kernel 3.13 sysfs read_descriptors() seemed to work OK. > > Proposal: > ========= > > Remove the usb_lock_device(udev) and usb_unlock_device(udev) from > devices/usb/core/sysfs.c in read_descriptors() that was added by the > kernel 3.13 commit > "232275a USB: fix substandard locking for the sysfs files" > > Any comments to this proposal ? It seems okay to me. Please submit a patch. So this removes the locking making the point about -EINTR in the first path moot. Signed-off-by: Oliver Neukum <oneukum@suse.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/usb/core')
-rw-r--r--drivers/usb/core/sysfs.c6
1 files changed, 1 insertions, 5 deletions
diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
index 7a6209314997..c953a0f1c695 100644
--- a/drivers/usb/core/sysfs.c
+++ b/drivers/usb/core/sysfs.c
@@ -843,16 +843,13 @@ read_descriptors(struct file *filp, struct kobject *kobj,
struct usb_device *udev = to_usb_device(dev);
size_t nleft = count;
size_t srclen, n;
- int cfgno, rc;
+ int cfgno;
void *src;
/* The binary attribute begins with the device descriptor.
* Following that are the raw descriptor entries for all the
* configurations (config plus subsidiary descriptors).
*/
- rc = usb_lock_device_interruptible(udev);
- if (rc < 0)
- return -EINTR;
for (cfgno = -1; cfgno < udev->descriptor.bNumConfigurations &&
nleft > 0; ++cfgno) {
if (cfgno < 0) {
@@ -873,7 +870,6 @@ read_descriptors(struct file *filp, struct kobject *kobj,
off -= srclen;
}
}
- usb_unlock_device(udev);
return count - nleft;
}