Re: [v11,1/4] drivers: jtag: Add JTAG core driver

[Russell King - ARM Linux <linux@armlinux.org.uk>]

On Tue, Nov 14, 2017 at 12:10:46PM +0100, gregkh@linuxfoundation.org wrote:
> On Tue, Nov 14, 2017 at 10:34:49AM +0000, Oleksandr Shamray wrote:
> > Greg, what you can suggest about it. May be better to add again single-open()-per-device lock with right locking way like:
> > 
> > >if (mutex_lock_interruptible(&jtag->open_lock)) {
> 
> You would stall an open?  Why not just return saying you can't do that?

Greg, I think you need to look at the code again.

>From the snippet in the email, this lock is not held while the device is
open, as you apparently think it is.  It's a short-term lock that is
held to ensure atomic access to the jtag->opened member, so that two
concurrent opens are unable to operate lock-step, resulting in
jtag->opened becoming 2.

The open function snippet in the email drops the lock as soon as it has
incremented jtag->opened, or encounters an error.

It seems entirely sensible, rather than using an atomic_t counter, as
it means that other openers are held off until the current opener has
either succeeded in opening the device or failed to open it.

-- 
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