Re: Kernel locking up in module

quoted

but the variable is non-null every other time I insert the module.

Are you adding any new devices after the init() routine executes ? You
seem to have exited the for loop due to bwusage becoming NULL, not the
dev (while both should be null).

You are not locking out the bottom half receive thread so it will

deadlock

Stephen, I don't understand how this is a deadlock ? His handler runs only
in the bottom half and he has no other code which runs in regular or hard
interrupt context. But you might want to try doing the mod_timer after
dropping
the lock to avoid a race (though not very likely ?). Unless it is
re-entrant,
which seems unlikely since he is using a 1 second timeout.

BTW, you are assigning 'data' in your routine, which is OK,
            unsigned long *data = (unsigned long *) ptr;
but if you reference it, that will crash the system since it is referring
to a local stack variable of another routine.

- KK



|---------+---------------------------->
|         |           N N Ashok        |
|         |           <nalkunda@egr.msu|
|         |           .edu>            |
|         |           Sent by:         |
|         |           netdev-bounce@oss|
|         |           .sgi.com         |
|         |                            |
|         |                            |
|         |           07/14/2003 04:35 |
|         |           PM               |
|         |                            |
|---------+---------------------------->
  >-----------------------------------------------------------------------------------------------------------------|
  |                                                                                                                 |
  |       To:       Stephen Hemminger [off-list ref]                                                         |
  |       cc:       netdev@oss.sgi.com                                                                              |
  |       Subject:  Re: Kernel locking up in module                                                                 |
  |                                                                                                                 |
  >-----------------------------------------------------------------------------------------------------------------|




On Monday 14 July 2003 18:49, Stephen Hemminger scrawled:

On Mon, 14 Jul 2003 17:46:30 -0400

N N Ashok [off-list ref] wrote:

quoted

Hi All,
    I am creating a module to measure the outgoing bandwidth usage on

the

quoted

interfaces. It uses the get_stats() of the device to get the current
stats and then computes the bandwidth usage. The algorithm for the

usage

quoted

calculation are borrowed from iproute2 package (tc/tc_estimator.c). The
problem is that the kernel keeps locking up. I am using rwlock_t locks

to

quoted

lock the data. In the code, I traverse the list of bwuage structures

and

quoted

as a debug message am printing whether the traversal ended in the
variable becoming null (which it should if everything went right), but
the variable is non-null every other time I insert the module.
         printk(KERN_INFO "bwestimator: dev: %s. bwusage: %s.\n", dev ?
"non-null" : "null", bwusage ? "non-null" : "null");

  I think this has got to do with some locking issues. As this is my
first go at the kernel locking, I might have used the wrong kind of
locks. I have attached the module source, header and the log messages

as

quoted

I inserted the module a couple of times. I request you all to please

help

quoted

me as I am totally lost here.

Thanks,
Ashok

You are not locking out the bottom half receive thread so it will

deadlock

when it runs while your code holds the top half lock.

Hi Stephen,
Thanks for the reply.
Do I used write_lock_bh()/write_unlock_bh() for my lock (bwusage_head_lock)

while still using read_lock() for dev_base_lock ?

Thanks,
Ashok