From b4a90d04ac79349799f65dfd7fa30b2aac6b2a4d Mon Sep 17 00:00:00 2001 From: Oliver Neukum Date: Thu, 21 Jan 2016 15:18:48 +0100 Subject: 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 Signed-off-by: Greg Kroah-Hartman --- drivers/usb/core/sysfs.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) (limited to 'drivers') 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; } -- cgit