as_arq scheduler alloc with 2.6.0-test8-mm1

Hi,

I am using 2.6.0-test8-mm1 kernel. I am using qlogic driver patch with
this kernel. Every time I insert qlogic driver my as_arq pool size
increases by 2000 objects of each size 76 bytes. I have kgdb setup and I
tried to put break point in various function in as_iosched.c to see if I
can see where it is getting allocated, but It never hit the breakpoint.
Can anyone tell me whether its as-i/o scheduler problem or something in
qlogic driver? How do I debug is problem?

After doing just insmod/rmmod for 20/30 times my machine runs out of
free pages. If I dont try to insert qlogic driver my system runs fine for
days without any problem. Following is the output of /proc/slabinfo for
as_arq after doing insmod/rmmod.

Any help as to how to debug this problem is
appreciated.

Thanks
Amit

[root@Host200-w2k root]# cat /proc/slabinfo |grep
as_arq
as_arq 6251 6300 76 50 1 :
tunables 32 16
0 : slabdata 126 126 0 : globalstat 165249
6300 1708
1538 0 1 82 : cpustat 245396 11366 247012
3502
[root@Host200-w2k root]# cat /proc/slabinfo |grep
as_arq
as_arq 8291 8300 76 50 1 :
tunables 32 16
0 : slabdata 166 166 0 : globalstat 167299
8298 1749
1539 0 1 82 : cpustat 247381 11530 247121
3502
[root@Host200-w2k root]#

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What qlogic driver patch is this?

Hi Andrew,

Qlogic driver I am using is from Micheal Bligh mjb1 patch. I have not applied the full patch just the qlogic driver.

Thanks
Amit

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Hi Andrew,

The qlogic driver is for Fibre Channel HBA QLA2342. This is a beta driver which is part of the mjb1 patch against 2.6.0-test8. As a part of driver insmod, driver tries to find fiber channel device and maps it to scsi block device. Actually I don't have any fibre channel target attached, so driver does not find any scsi devices and discovery finishes without adding any block device.

I am trying to go through driver scsi_scan process and see when does actual allocation from as_arq happens. But for some reason after going to kgdb I get SIGEMT and I cannot debug further. What is causing SIGEMT cause after doing some search looks like its actually SIGUSR but linux treats it as SIGEMT. Is there any way to prevent SIGEMT when I want to use kgdb ?

Thanks for your help,

Amit

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SIGEMT is kgdb's way of telling you the kernel oopsed. The different signal types used to convey useful information (a different type for NMI watchdog expiry, for example). But George then randomised them and I've never worked out the new scheme...

kgdb is difficult to use with kernel modules. There's probably a way of doing it in 2.6 but I've never sat down and worked it out. But as you appear to be working on the SCSI core that's not a problem.

Hi Amit,

I'm a little bit busy to look at this now, however someone is looking into all these refcounting problems.

If you would like to narrow it down a bit, check that the request queues that are allocated are all released when the driver is unloaded (drivers/block/ll_rw_blk.c blk_alloc_queue and blk_cleanup_queue). Just stick a couple of printks there if your debugger isn't working.

Hi

After doing some printk debugging looks like for each block device we allocate elevator structure. But during cleanup the elevator->elevator_data is never freed. In printk I put printk in as-iosched.c:as_alloc where I see elevator_data is allocated from as_arq pool and it should have been freed as a part of block device cleanup through elevator_release function. I never see it coming to elevatore_release function.

I will try to walk through code some more and see if I can figure out who was supposed to call elevator_release as part of cleanup. Let me know if I am going on wrong track here.

Thanks
Amit

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