Semaphore

[Kosta Zertsekel]

>> >> 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...
>>
> In this (fictional, I've not looked at the serial driver code) example I'm
> assuming a semaphore owned by a driver. The user space application is using
> the driver through a device node. The semaphore is managed by the driver,
> and released when the close is called.
> The driver does not know how (or even if) the application stopped, only
> that it closed the file descriptor.
>
> What specific type of semaphore are you interested in? Who acquires it,
> what does it protect?

I think of user land program opening a socket and crashing on
segmentation fault.
In code 'socket' syscall does:
    sock_map_fd --> sock_alloc_file --> alloc_file --> ... get lost ...
Where exactly in this case lock is held - I mean the lock that gets
released when user land process dies?
Thanks,
--- KostaZ