SCSI Tape driver problem

SCSI Tape driver problem

[vijay srinath]

hello all,

    I noticed a bug in the scsi tape class driver in kernel 2.2.16/2.4.x.
This is the test that i ran. 
1. I have two scsi-fc tape devices
2. I insert the hba driver, so that both the tape devices are enabled and map to st0 and st1
3. I remove the device that maps to st0 using 
   echo "scsi remove-single-device 0 0 0 0" > /proc/scsi/scsi
4. Now, if i try to do an open("/dev/st1",..), the process hangs as the open call never returns.

    The problem seems to be in the callback function st_sleep_done() where the following comparison is being made
if ((st_nbr = TAPE_NR(SCpnt->request.rq_dev)) < st_template.nr_dev) 
{
 ...
}

This comparision fails for the above test since nr_dev will be 1 and 
TAPE_NR() will also be 1 for /dev/st1. Hence the semaphore 
SCpnt->request.sem never gets released and open waits forever.


    Can somebody please let me know why this comparison is needed ?

regards
vijay



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Re: SCSI Tape driver problem

[Kai Makisara]

On Tue, 31 Jul 2001, vijay srinath wrote:

> hello all,
>
>     I noticed a bug in the scsi tape class driver in kernel 2.2.16/2.4.x.
> This is the test that i ran.
> 1. I have two scsi-fc tape devices
> 2. I insert the hba driver, so that both the tape devices are enabled and map to st0 and st1
> 3. I remove the device that maps to st0 using
>    echo "scsi remove-single-device 0 0 0 0" > /proc/scsi/scsi
> 4. Now, if i try to do an open("/dev/st1",..), the process hangs as the open call never returns.
>
>     The problem seems to be in the callback function st_sleep_done() where the following comparison is being made
> if ((st_nbr = TAPE_NR(SCpnt->request.rq_dev)) < st_template.nr_dev)
> {
>  ...
> }
>
> This comparision fails for the above test since nr_dev will be 1 and
> TAPE_NR() will also be 1 for /dev/st1. Hence the semaphore
> SCpnt->request.sem never gets released and open waits forever.
>
>
>     Can somebody please let me know why this comparison is needed ?
>
The test was inserted a long time ago to be an additional safeguard
against problems in the code. In normal operation the interrupt function
should never be called with an illegal argument. It seems that the world
around the test has evolved so that the test is not working properly any
more.

You can just remove the test. I will prepare a patch to fix this bug and
send the patch to Linus.

	Kai