[linux-lvm] Re: System hangs after echo value > /sys/block/dm-0/queue/nr_requests

[linux-lvm] Re: System hangs after echo value > /sys/block/dm-0/queue/nr_requests

[Andrew Morton]

Miquel van Smoorenburg <miquels@cistron.nl> wrote:
>
> If you echo a value (any value; for example the default 128) to
> /sys/block/dm-0/queue/nr_requests the shell you are in hangs.
> After about 5 seconds, the whole system hangs 100%.

hm, nice.  It does the same thing for /sys/block/md0/queue/nr-requests.

With CONFIG_DEBUG_SPINLOCK enabled we go BUG in __wake_up():

Program received signal SIGTRAP, Trace/breakpoint trap.
__wake_up (q=0xcf299e90, mode=3, nr_exclusive=1) at include/asm/spinlock.h:137
137                     BUG();
(gdb) bt
#0  __wake_up (q=0xcf299e90, mode=3, nr_exclusive=1) at include/asm/spinlock.h:137
#1  0xc02cc847 in queue_requests_store (q=0xcf299df8, page=0xe <Address 0xe out of bounds>, count=14)
    at drivers/block/ll_rw_blk.c:2843
#2  0xc02cc907 in queue_attr_store (kobj=0xcf299f68, attr=0xe, page=0xe <Address 0xe out of bounds>, 
    length=14) at drivers/block/ll_rw_blk.c:2892
#3  0xc01aa84f in flush_write_buffer (file=0xe, buffer=0xc0456100, count=14) at fs/sysfs/file.c:205
#4  0xc01aa8ac in sysfs_write_file (file=0xc0493550, buf=0xe <Address 0xe out of bounds>, count=2, 
    ppos=0xc851cf84) at fs/sysfs/file.c:233
#5  0xc016f458 in vfs_write (file=0xc0493550, buf=0x80b2d00 "128\n", count=4, pos=0xc851cf84)
    at fs/read_write.c:257
#6  0xc016f55e in sys_write (fd=14, buf=0xe <Address 0xe out of bounds>, count=14) at fs/read_write.c:293


Where queue_requests_store() does wake_up(&rl->wait[READ]);

It looks like nobody has called blk_init_queue() for this queue and the
waitqueue head is uninitialised.

No md was in use on this machine: it was simply enabled in kernel config.

[linux-lvm] Re: System hangs after echo value > /sys/block/dm-0/queue/nr_requests

[Mike Christie]

[-- Attachment #1: Type: text/plain, Size: 451 bytes --]

Andrew Morton wrote:

> Where queue_requests_store() does wake_up(&rl->wait[READ]);
> 
> It looks like nobody has called blk_init_queue() for this queue and the
> waitqueue head is uninitialised.
> 

DM, MD, rd and loop use blk_alloc_queue and blk_queue_make_request to 
initialize their queue, because they only use the make_request_fn. The 
attached patch prevents the queue from being registered if only 
blk_alloc_queue was called.

Mike Christie

[-- Attachment #2: queue_attr.patch --]
[-- Type: text/plain, Size: 573 bytes --]

--- linux-2.6.0-orig/drivers/block/ll_rw_blk.c	2003-12-28 23:09:16.000000000 -0800
+++ linux-2.6.0/drivers/block/ll_rw_blk.c	2003-12-30 16:11:00.690504036 -0800
@@ -2902,7 +2902,7 @@ int blk_register_queue(struct gendisk *d
 
 	request_queue_t *q = disk->queue;
 
-	if (!q)
+	if (!q || !q->request_fn)
 		return -ENXIO;
 
 	q->kobj.parent = kobject_get(&disk->kobj);
@@ -2929,7 +2929,7 @@ void blk_unregister_queue(struct gendisk
 {
 	request_queue_t *q = disk->queue;
 
-	if (q) {
+	if (q && q->request_fn) {
 		elv_unregister_queue(q);
 
 		kobject_unregister(&q->kobj);

[linux-lvm] Re: System hangs after echo value > /sys/block/dm-0/queue/nr_requests

[Jens Axboe]

On Tue, Dec 30 2003, Mike Christie wrote:
> Andrew Morton wrote:
> 
> >Where queue_requests_store() does wake_up(&rl->wait[READ]);
> >
> >It looks like nobody has called blk_init_queue() for this queue and the
> >waitqueue head is uninitialised.
> >
> 
> DM, MD, rd and loop use blk_alloc_queue and blk_queue_make_request to 
> initialize their queue, because they only use the make_request_fn. The 
> attached patch prevents the queue from being registered if only 
> blk_alloc_queue was called.

I'm fine with that patch since we don't have any attributes in there
that apply to just remappers.

-- 
Jens Axboe