-----Original Message-----
From: Chip Bilbrey [mailto:chip-Gz1Ta9Qd61ZAfugRpC6u6w@public.gmane.org]
Sent: Monday, November 6, 2017 12:33 AM
To: Oleksandr Shamray <oleksandrs-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
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Subject: Re: [v11,1/4] drivers: jtag: Add JTAG core driver


Oleksandr Shamray writes:

[..]

I notice the single-open()-per-device lock was dropped by request in an earlier
revision of your patches, but multiple processes trying to drive a single JTAG
master could wreak serious havoc if transactions get interleaved. Would
something like an added JTAG_LOCKCHAIN/UNLOCKCHAIN
ioctl() for exclusive client access be reasonable to prevent this?

Yes, it dropped by recommendation of Greg KH [off-list ref]. 

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)) {
return -ERESTARTSYS;
}

if (jtag->opened) {
mutex_unlock(&jtag->open_lock);
return -EINVAL;
}

nonseekable_open(inode, file);
file->private_data = jtag;
jtag->opened++;
mutex_unlock(&jtag->open_lock);

Thaks.

-Chip

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