Re: [PATCH 002 of 6] md: Change lifetime rules for 'md' devices.

[Neil Brown]

On Tuesday October 31, akpm@xxxxxxxx wrote:
> On Tue, 31 Oct 2006 17:00:51 +1100
> NeilBrown <neilb@xxxxxxx> wrote:
> 
> > Currently md devices are created when first opened and remain in existence
> > until the module is unloaded.
> > This isn't a major problem, but it somewhat ugly.
> > 
> > This patch changes the lifetime rules so that an md device will
> > disappear on the last close if it has no state.
> 
> This kills the G5:
> 
> 
> EXT3-fs: recovery complete.
> EXT3-fs: mounted filesystem with ordered data mode.
> Oops: Kernel access of bad area, sig: 11 [#1]
> SMP NR_CPUS=4 
> Modules linked in:
> NIP: C0000000001A31B8 LR: C00000000018E5DC CTR: C0000000001A3404
> REGS: c0000000017ff4a0 TRAP: 0300   Not tainted  (2.6.19-rc4-mm1)
> MSR: 9000000000009032 <EE,ME,IR,DR>  CR: 84000048  XER: 00000000
> DAR: 6B6B6B6B6B6B6BB3, DSISR: 0000000040000000
> TASK = c00000000ff2b7f0[1899] 'nash' THREAD: c0000000017fc000 CPU: 1
> GPR00: 0000000000000008 C0000000017FF720 C0000000006B26D0 6B6B6B6B6B6B6B7B 
..
> NIP [C0000000001A31B8] .kobject_uevent+0xac/0x55c
> LR [C00000000018E5DC] .__elv_unregister_queue+0x20/0x44
> Call Trace:
> [C0000000017FF720] [C000000000562508] read_pipe_fops+0xd0/0xd8 (unreliable)
> [C0000000017FF840] [C00000000018E5DC] .__elv_unregister_queue+0x20/0x44
> [C0000000017FF8D0] [C000000000195548] .blk_unregister_queue+0x58/0x9c
> [C0000000017FF960] [C00000000019683C] .unlink_gendisk+0x1c/0x50
> [C0000000017FF9F0] [C000000000122840] .del_gendisk+0x98/0x22c

I'm guessing we need

diff .prev/block/elevator.c ./block/elevator.c
--- .prev/block/elevator.c	2006-10-31 20:06:22.000000000 +1100
+++ ./block/elevator.c	2006-10-31 20:06:40.000000000 +1100
@@ -926,7 +926,7 @@ static void __elv_unregister_queue(eleva
 
 void elv_unregister_queue(struct request_queue *q)
 {
-	if (q)
+	if (q && q->elevator)
 		__elv_unregister_queue(q->elevator);
 }


Jens?  md never registers and elevator for its queue.

> 
> Also, it'd be nice to enable CONFIG_MUST_CHECK and take a look at a few
> things...
> 
> drivers/md/md.c: In function `bind_rdev_to_array':
> drivers/md/md.c:1379: warning: ignoring return value of `kobject_add', declared with attribute warn_unused_result
> drivers/md/md.c:1385: warning: ignoring return value of `sysfs_create_link', declared with attribute warn_unused_result
> drivers/md/md.c: In function `md_probe':
> drivers/md/md.c:2986: warning: ignoring return value of `kobject_register', declared with attribute warn_unused_result
> drivers/md/md.c: In function `do_md_run':
> drivers/md/md.c:3135: warning: ignoring return value of `sysfs_create_group', declared with attribute warn_unused_result
> drivers/md/md.c:3150: warning: ignoring return value of `sysfs_create_link', declared with attribute warn_unused_result
> drivers/md/md.c: In function `md_check_recovery':
> drivers/md/md.c:5446: warning: ignoring return value of `sysfs_create_link', declared with attribute warn_unused_result

I guess... I saw mail a while ago about why we really should be
checking those.  I'll have to dig it up again.

NeilBrown
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