lkml.org 
[lkml]   [2005]   [Aug]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
Subjectusage count in device driver and concurrency
Hi,
I am wondering how to handle device usage count in
open and release call of device driver if hardware
need to be initialized on first open and shutdown on
last close. I have seen som code like

int open()
{
/*some code*/
device->usage++;
if(device->usage==1)
init_hardware();
/*rest of code*/
}
void release ()
{
/*some code*/
if(device->usage==1)
shutdown_hardware();
device->usage--;
/*rest of code*/
}



However, it seems to me that this code can make
problem.
If device->usage=0, and two process A,B execute line
device->usage++;
concurretly, device->usage will become 2 when they
come to next line. This will result in hardware being
used without initialization. Same things can happen in
release call also, which will result in no shutdown of
hardware.
I have seen this type of code in
/linux-2.6.8/drivers/ide/ide-disk.c and
/linux-2.6.8/drivers/ide/ide-floppy.c

Please let me know if its bug or not before I
start working on patches.


Regards,
Tushar

__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-08-30 16:24    [W:0.062 / U:3.100 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site