linux-kernel - Re: [LTP] [PATCH] Synchronization required before release the lock: sem

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Date:	Wed, 3 Mar 2010 11:30:42 +0530
From:	naresh kamboju <naresh.kernel@...il.com>
To:	Rishikesh K Rajak <risrajak@...ux.vnet.ibm.com>
Subject: Re: [LTP] [PATCH] Synchronization required before release the lock: 
	sem_post/8-1.c

On Wed, Mar 3, 2010 at 10:26 AM, Rishikesh K Rajak
<risrajak@...ux.vnet.ibm.com> wrote:
> On Tue, Mar 02, 2010 at 08:38:20PM +0530, naresh kamboju wrote:
>> On Tue, Mar 2, 2010 at 2:20 PM, Rishikesh K Rajak
>> <risrajak@...ux.vnet.ibm.com> wrote:
>> > I feel before getting semaphore value, we need to sync first so here
>> > sleep is require,though your point is valid that there is no use of
>> > using sleep inside while loop.
>> I agree with you.
>> AFAIU, we should call sleep() before calling getting semaphore
>> value.when we don't have while loop here. Because while loop condition
>> is depends on val so when ever we call sem_getvalue() it will get
>> latest value of val.
>> In addition to this, we are ensuring val is decremented before we do
>> unlock the sem by while loop condition.
>>
>> Having sleep() in while loop will not effect the final output. IIUC
>>
>
> Hi Naresh,
>
> I am not able to apply your patch against ltp next branch. can you
> please send me patch against next branch of ltp ?
Here I have posted and attached to this e-mail.

Signed-off-by: Naresh Kamboju < naresh.kernel@...il.com >

---
 testcases/open_posix_testsuite/conformance/interfaces/sem_post/8-1.c
|   15 	8 +	7 -	0 !
 1 file changed, 8 insertions(+), 7 deletions(-)

Index: b/testcases/open_posix_testsuite/conformance/interfaces/sem_post/8-1.c
===================================================================
--- a/testcases/open_posix_testsuite/conformance/interfaces/sem_post/8-1.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/sem_post/8-1.c
@@ -161,7 +161,6 @@ int main()
 	}
 	fprintf(stderr, "P: child_1:%d forked\n", c_1);
 	
-	sleep(1);
 	c_2 = fork();
 	if (c_2 == 0)
 	{
@@ -176,13 +175,13 @@ int main()
 	}
 	fprintf(stderr, "P: child_2: %d forked\n", c_2);

+        /* Step 3 Implementation */
 	/* Make sure the two children has been waiting */	
-	/*do {
-		sleep(1);
+	do {
 		sem_getvalue(sem_1, &val);
 		//printf("val = %d\n", val);
 	} while (val != 1);
-	*/
+
 	c_3 = fork();
 	if (c_3 == 0)
 	{
@@ -191,13 +190,15 @@ int main()
 	}
 	fprintf(stderr, "P: child_3: %d forked\n", c_3);
 	
+        /* Step 3 Implementation */
 	/* Make sure child 3 has been waiting for the lock */	
-	/*do {
-		sleep(1);
+	do {
 		sem_getvalue(sem_1, &val);
 		//printf("val = %d\n", val);
 	} while (val != 0);
-	*/
+
+	/* Synchronization required before release the lock */
+	sleep(1);
 	/* Ok, let's release the lock */
 	fprintf(stderr, "P: release lock\n");
 	sem_post(sem);

Best regards
Naresh Kamboju
>
> #git clone -b next
> git://ltp.git.sourceforge.net/gitroot/ltp/ltp-dev.git ltp
>
> And then create your patch and send it to ltp-list@
>
> --
> Thanks & Regards
> Rishi
> LTP Maintainer
> IBM, LTC, Bangalore
> Please join IRC #ltp @ irc.freenode.net
>

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