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Date: Thu, 13 May 2004 16:47:55 +0800
From: fisherman <fishermandong@yahoo.com.cn>
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To: linux-kernel@vger.kernel.org
Subject: sleep in make_request_fn() casue system no response(2.4.20-8)
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Hello,

   I am writting a virtual device driver, I found that if I add sleep
into function make_request_fn(), then use dd to copy 100M  data to the
corresponding device, the system goes dead(keyboard & mouse have no
response, can't login by telnet).

   I also tried to add sleep into LVM's driver, and the test result is
similar to our driver do, the test about LVM is shown as follws:

[1] source modification
-------- source begin --------
static int lvm_make_request_fn(request_queue_t * q,
                               int rw, struct buffer_head *bh)
{
        current->state = TASK_INTERRUPTIBLE;  /* newly added */
        schedule_timeout(1);                  /*newly added*/
        return (lvm_map(bh, rw) <= 0) ? 0 : 1;
}   
-------- source end --------

[2] test 1
   after building the module, the system will go dead if I run the
folling command to write data to a LV(100M bye ONE command):
#dd if=/dev/zero of=/dev/vg_data1/dlv3 bs=1024 count=100000

[3] test 2
    but write operation with smaller size can be repeated many times, the
following script runs OK.
-------- script begin --------
#write 10M for 10 times
i=0
pos=0
cnt=10000
while [ $i -lt 10 ] 
do
dd if=/dev/zero of=/dev/vg_data1/dlv3 bs=1024 count=$cnt seek=$pos
i=`expr $i + 1`
pos=`expr $pos + $cnt`
done
-------- script end --------

[4] environment
    redhat 9;
    kernel 2.4.20-8.
    
    I repeated test 1 and test 2 for many times, ant the result are the
same.

Can anyone tell me the reason?

thanks.