Messages in this thread | | | From | "Alexandr Sandler" <> | Subject | Requests never returning? | Date | Wed, 5 Jun 2002 01:29:26 +0200 |
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Hi list.
I am working on a logical volume manager (yep, another one) driver for Linux. I implemented block device driver that used to receive requests and to redirect them to scsi disks (by changing bh->b_rdev and bh->b_rsector). I am experiencing a problem with my driver and I was wondering if anyone can help me with it.
Notice that scsi disks sitting on SAN.
The driver, as it is, seems to be quite stable. I confident it can run for weeks under the most heavy stress test, despite I only tried 48 hours tests. But sometimes, very rarely, something goes wrong and process doing I/O (on the logical volume + file system) getting stacked. Call trace (from kdb) looks like this. Process trying to do generic_file_read() (or ..._write()) and, eventually, getting into lock_page() - this is where it's getting stacked. What seems to be obvious (for me - correct me if I am wrong), is that process supposed to succeed locking page, but buffer_head using this page is never getting it's b_end_io() and here we go - it's stacked.
This is happening, usually, when one or several computers on SAN getting restarted and as a result making a lot of noise (LIPs) on fiber. And it's even more strange because I made special tests to reveal the conditions needed for this to happen. I caused hundreds of LIPs, but Linux box was stable and test was running - it was couple of month ago. And now it happened once again - when I rebooted some lame NetWare host.
I think the problem is not with my driver (yes, I know it's better to be paranoiac in this things), despite I never tried to do some stress tests with scsi disks - without my driver.
So, my question is like this. Is there any condition, under which I/O requests may not return (even with error), when working with SAN?
Here are some specs: It's Pentium III 800 MHz UP with 256Mb of RAM. Kernel 2.4.16 (as far as I remember there was no major changes and bugfixes in scsi layer in 2.4.17 and 2.4.18, so I think it doesn't really matter if I use 2.4.16 or 2.4.18 - once again, correct me if I am wrong) . I am using RedHat 7.1 distro. Two Qlogic 2200 optical HBAs powered by qlogic 4.27b driver (this part may seem to be crucial - I never tried to work with other versions of their drivers. On the other hand, I never had a reason to doubt stability of this version). SAN sitting on Gadzoox Capellix 3000 - arbitrated loop (I got the same behavour with Brocade switch - don't remember the model).
Thanks in advance for any help.
Alexandr Sandler.
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