Semaphore

[Kosta Zertsekel]

On Fri, Feb 24, 2012 at 11:04 AM, Kristof Provost <kristof at sigsegv.be> wrote:
> On 2012-02-24 09:07:40 (+0200), Kosta Zertsekel <zertsekel at gmail.com> wrote:
>> >> > Imagine a driver which only one app can use at a time (perhaps a serial
>> >> > port). The kernel will take a lock when the user space app open()s the
>> >> > device node and release it when it close()s.
>> >> > If the app segfaults in between the open() and close() the lock will
>> >> > still get released. The kernel always cleans up open files for stopped
>> >> > processes, regardless of how they stop. During this cleanup the kernel
>> >> > will close() the device node, and as a result the driver will release
>> >> > the lock.
>>
>> Can you please point to some code in Linux Kernel that does the job?
>
> In kernel/exit.c, look at do_exit(). It cleans up a process after it's
> terminated (for whatever reason).
> It does a lot of cleanup, but through exit_files() -> put_files_struct()
> -> close_files() it ends up iterating over all open file descriptors and
> closing them.
> What's done for each close depends on what the process had open. Normal
> files will just be closed, or a TCP socket might be closed, or if a
> device node was opened the corresponding drivers close() function will
> be called.

I meant that I don't see any semaphore related stuff in do_exit().
It seems that semaphore just remains there in the system after a user
land task is killed...

--- KostaZ