down_interruptible() return non-zero value once signal is received and trying down_interruptible again in loop return value is always non-zero

[anish singh]

On Fri, Oct 18, 2013 at 5:26 AM, Mushtaq Khan <mushtaqkhan921 at gmail.com> wrote:
> Hi,
>
> In kernel driver, using Semaphore to block on resources (Descriptors and
> memory).
> Semaphore is initialized in locking state using call "init_MTEX_LOCKED()",
> when resources are not available process calls down_interruptible() and
> blocks. Once resources are freed up() is called, and blocked process is
> unblocked. up() is called from interrupt context which frees resources on
> receiving ACK-Interrupt.
> Following is the code snippet for blocking:
> do {
>     ret = down_interruptible(sem)
>     if (ret == 0) {
>         break;
>     } else {
>         printk("Semaphore is not acquired try again\n");
>         continue;
>    }
> } while (1);
>
> While loop is used to make sure down_interrptible() is called until process
> acquires the semaphore. If process receives signal, process unblocks from
> down_interrptible() without acquiring the semaphore.
> Issue am seeing is once signal is received under the blocking state, again
> trying to acquire semaphore using down_interruptible() return value is
> always non-zero and process is looping in while loop.
Please post your full code here.
>
> Can someone explain this behavior, I wrote the code with expectation that
> after signal is received again trying to acquire lock will either block the
> process or process will get semaphore.
> Please help me on this.
>
> Thanks,
> Mushtaq Khan
>
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