Hi,
Pls see inline
Jan Hudec <bulb@ucw.cz>@nl.linux.org on 06/10/2004 06:30:34 PM
Sent by: kernelnewbies-bounce@nl.linux.org
To: Amit Kumar Singh/HSS@HSS
cc: Anandraj <arm@tataelxsi.co.in>, "'l x'" <whereisit28@yahoo.com>,
kernelnewbies@nl.linux.org
Subject: Re: Help - can not rmmod a module
On Thu, Jun 10, 2004 at 18:07:16 +0530, aksingh@hss.hns.com wrote:
> Just a doubt on this -- what happens, when an application using the
module
> crashes. The application had done a MOD_INC_USE_COUNT and then it
crashed,
> so the module stays for ever unless the pc is rebooted . The module may
be
> working perfectly alright, just that it cannot eb removed.
No. It's NOT the application doing MOD_INC_USE_COUNT. It is kernel.
######### Yes I meant the same, the application doing an open, and
MOD_INC_USE_COUNT being done inside open for that driver
> This can prove to be a problem for say a char device.
>
> someone opens it, MOD_INC_USE_COUNT is incremented in the open() call,
then
> the application that opened it crashes. so the module cannot be removed.
> Now someone starts that process again, and calls the open function again,
> will it work.
It would be just the same problem for filesystems, sockets, pipes,
everything... No, it is not a problem. The thing is, that the use count
is held by the file descritor, which is reference-counted. When
application's file descriptor array is freed (during destruction of it's
context). When it's refcount goes zero (several processes may use it),
the generic device close calls close from your device descriptor and
decrements module refcount.
> It will but then this shows that doing something like this -- if
> (MOD_IN_USE) return -EBUSY in the char device open() function might be a
> foolish thing to do, even if u assume that one and only one user level
> process would be accessing your module.
################ so you mean having this as the first statement in the char
device open function if(MOD_IN_USE) return -EBUSY, not a problem ?,i.e if a
user level process using a module crashes after doing MOD_INC_USE_COUNT, it
is not a problem as when the reference count for the fd falls to zero, the
close for the fd would automatically be called, to decrement the usage
count, and then the module can be succesfully removed using rmmod ??
##########################
> regards
> Amit
-------------------------------------------------------------------------------
Jan 'Bulb' Hudec <bulb@ucw.cz>
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