diff options
author | Oliver Neukum <oneukum@suse.com> | 2016-01-21 15:18:48 +0100 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-02-03 13:29:12 -0800 |
commit | b4a90d04ac79349799f65dfd7fa30b2aac6b2a4d (patch) | |
tree | 118b7d516443bbd7e265d2d20162c7e55ed8f232 /drivers/usb/core | |
parent | 7dd9cba5bb90ffa9c60c1533b715dc91c5082cd9 (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.c | 6 |
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; } |