All,

While adding support for the new change_queue_depth/type() callbacks,

        static int
        qla2x00_change_queue_depth(struct scsi_device *sdev, int qdepth)
        {
                scsi_adjust_queue_depth(sdev, scsi_get_tag_type(sdev), qdepth);
                return sdev->queue_depth;
        }

and updating the queue-depth:

        # echo 16 > /sys/class/scsi_device/3:0:0:0/device/queue_depth

while I/O is running, I'm hitting a reproducible WARN_ON() triggering
within as_completed_request():

        static void as_completed_request(request_queue_t *q, struct request *rq)
        {
                struct as_data *ad = q->elevator->elevator_data;
                struct as_rq *arq = RQ_DATA(rq);

                WARN_ON(!list_empty(&rq->queuelist));
                ...

and a subsequent panic:

        Badness in as_completed_request at drivers/block/as-iosched.c:951

        Call Trace: <IRQ> ffff8024883a>{as_completed_request+63} 
<ffffffff8024098d>{elv_completed_request+44}
               <ffffffff8024272a>{__blk_put_request+73} 
<ffffffff80280781>{scsi_end_request+164}
               <ffffffff802809eb>{scsi_io_completion+584} 
<ffffffff80297059>{sd_rw_intr+709}
               <ffffffff8027aa08>{scsi_finish_command+182} 
<ffffffff8027b2dc>{scsi_softirq+255}
               <ffffffff801291ea>{__do_softirq+110} 
<ffffffff8010eb13>{call_softirq+31}
               <ffffffff801101be>{do_softirq+54} <ffffffff80110211>{do_IRQ+74}
               <ffffffff8010deba>{ret_from_intr+0}  <EOI> 
<ffffffff8010c2fd>{mwait_idle+86}
               <ffffffff8021aef0>{acpi_processor_idle+310} 
<ffffffff8010cacb>{cpu_idle+79}
               <ffffffff804cecbf>{start_secondary+1017}
        ----------- [cut here ] --------- [please bite here ] ---------
        Kernel BUG at "drivers/block/ll_rw_blk.c":2361
        invalid operand: 0000 [1] SMP
        CPU 2
        Modules linked in: qla2xxx
        Pid: 0, comm: swapper Not tainted 2.6.13-rc5
        RIP: 0010:[<ffffffff80242734>] <ffffffff80242734>{__blk_put_request+83}
        RSP: 0018:ffff8100021bbde8  EFLAGS: 00010087
        RAX: 0000000000000000 RBX: ffff81002dc738b0 RCX: 0000000000008000
        RDX: 0000000000004e6b RSI: 0000000000000004 RDI: ffff81003e091778
        RBP: ffff81003f8fa600 R08: 0000000000000000 R09: 0000000000000003
        R10: 00000000ffffffff R11: 0000000000000000 R12: 0000000000000000
        R13: 0000000000000001 R14: ffff81003f8fa600 R15: ffff81003f8fa600
        FS:  0000000000000000(0000) GS:ffffffff804b6900(0000) 
knlGS:0000000000000000
        CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
        CR2: 00002aaaaaac1000 CR3: 0000000037f05000 CR4: 00000000000006e0
        Process swapper (pid: 0, threadinfo ffff8100021b6000, task 
ffff8100021b54f0)
        Stack: ffff81002dc738b0 ffff81002c1cd7c0 0000000000000286 
ffffffff80280781
               0000000000000001 ffff81002c1cd7c0 ffff81002dc738b0 
0000000000000000
               0000000000080000 ffffffff802809eb
        Call Trace: <IRQ> <ffffffff80280781>{scsi_end_request+164} 
<ffffffff802809eb>{scsi_io_completion+584}
               <ffffffff80297059>{sd_rw_intr+709} 
<ffffffff8027aa08>{scsi_finish_command+182}
               <ffffffff8027b2dc>{scsi_softirq+255} 
<ffffffff801291ea>{__do_softirq+110}
               <ffffffff8010eb13>{call_softirq+31} 
<ffffffff801101be>{do_softirq+54}
               <ffffffff80110211>{do_IRQ+74} <ffffffff8010deba>{ret_from_intr+0}
                <EOI> <ffffffff8010c2fd>{mwait_idle+86} 
<ffffffff8021aef0>{acpi_processor_idle+310}
               <ffffffff8010cacb>{cpu_idle+79} 
<ffffffff804cecbf>{start_secondary+1017}

        Code: 0f 0b a3 0b f2 32 80 ff ff ff ff c2 39 09 48 89 de 48 89 ef
        RIP <ffffffff80242734>{__blk_put_request+83} RSP <ffff8100021bbde8>
         <3>Debug: sleeping function called from invalid context at 
include/linux/rwsem.h:43
        in_atomic():1, irqs_disabled():1

        Call Trace: <IRQ> <ffffffff8011e2d7>{__might_sleep+199} 
<ffffffff80125316>{profile_task_exit+34}
               <ffffffff80126fe2>{do_exit+34} 
<ffffffff801fc7d0>{vgacon_cursor+231}
               <ffffffff8010f653>{kernel_math_error+0} 
<ffffffff8010fa09>{do_trap+264}
               <ffffffff8010feb9>{do_invalid_op+145} 
<ffffffff80242734>{__blk_put_request+83}
               <ffffffff801245d7>{printk+141} <ffffffff8010e415>{error_exit+0}
               <ffffffff80242734>{__blk_put_request+83} 
<ffffffff8024272a>{__blk_put_request+73}
               <ffffffff80280781>{scsi_end_request+164} 
<ffffffff802809eb>{scsi_io_completion+584}
               <ffffffff80297059>{sd_rw_intr+709} 
<ffffffff8027aa08>{scsi_finish_command+182}
               <ffffffff8027b2dc>{scsi_softirq+255} 
<ffffffff801291ea>{__do_softirq+110}
               <ffffffff8010eb13>{call_softirq+31} 
<ffffffff801101be>{do_softirq+54}
               <ffffffff80110211>{do_IRQ+74} <ffffffff8010deba>{ret_from_intr+0}
                <EOI> <ffffffff8010c2fd>{mwait_idle+86} 
<ffffffff8021aef0>{acpi_processor_idle+310}
               <ffffffff8010cacb>{cpu_idle+79} 
<ffffffff804cecbf>{start_secondary+1017}

        Kernel panic - not syncing: Aiee, killing interrupt handler!

Adding scsi_target_quiesce() and scsi_target_resume() barriers around
the scsi_adjust_target_queue_depth() call appears to help (i.e.
dropping from 32 -> 24):

        # echo 24 > /sys/class/scsi_device/3\:0\:0\:0/device/queue_depth

and dropping down again to 16:

        # echo 16 > /sys/class/scsi_device/3\:0\:0\:0/device/queue_depth

but occasionally, while trying another depth drop:

        # echo 10 > /sys/class/scsi_device/3\:0\:0\:0/device/queue_depth

I'll either get a panic (haven't captured a good one yet (only a
couple of line within the trace):

        eip: ffffffff80248a62
        ----------- [cut here ] --------- [please bite here ] ---------
        Kernel BUG at "include/asm/spinlock.h":121

or I get the following slab-error:

        slab error in cache_free_debugcheck(): cache `size-128': double free, 
or memory outside object was overwritten

        Call Trace:<ffffffff8014930c>{cache_free_debugcheck+290} 
<ffffffff8014975c>{kfree+136}
               <ffffffff80244e65>{blk_queue_resize_tags+119} 
<ffffffff8027a826>{scsi_adjust_queue_depth+68}
               <ffffffff88000133>{:qla2xxx:qla2x00_change_queue_depth+71}
               <ffffffff80283666>{sdev_store_queue_depth_rw+82} 
<ffffffff8023a9a2>{dev_attr_store+31}
               <ffffffff80191e95>{sysfs_write_file+200} 
<ffffffff80160dba>{vfs_write+172}
               <ffffffff80160ed8>{sys_write+69} 
<ffffffff8010d8f6>{system_call+126}

        ffff8100389baba8: redzone 1: 0x170fc2a5, redzone 2: 0x0.

I'm using a fairly recent snapshot of Linus' GIT tree (sync done
earlier today).

Two questions:

 - must the target be quiesced before adjusting the queue-depth?

 - any ideas on where why successive lowering of the depth borks the
   machine?

Thanks,
Andrew Vasquez
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