Re: kernel BUG at drivers/block/cciss.c:1260! (with recent linux-2.6 tree)

[Jens Axboe <jens.axboe@oracle.com>]

On Tue, Jan 29 2008, Jens Axboe wrote:
> On Tue, Jan 29 2008, Andrew Vasquez wrote:
> > On Tue, 29 Jan 2008, Jens Axboe wrote:
> > 
> > > Great, thanks for confirming. It does look like a clear bug in cciss, it
> > > just got exposed now that it uses proper end request handling. We never
> > > need to clear ->data_len, since for blk_fs_request() it will be cleared
> > > on init. So just setting a residual count there for blk_fs_request()
> > > like cciss does is fine.
> > > 
> > > Anyway, it's in my pending queue for Linus.
> > > 
> > 
> > 
> > Hmm, probably not related to the block changes in your tree, but I'm
> > seeing yet another problem after working (compile jobs) the machine:
> > 
> > 	[   61.423922] BUG: spinlock recursion on CPU#2, kjournald/2317
> > 	[   61.427843]  lock: ffff81042c5a4988, .magic: dead4ead, .owner: kjournald/2317, .owner_cpu: 2
> > 	[   61.427843] Pid: 2317, comm: kjournald Not tainted 2.6.24 #45
> > 	[   61.427843] 
> > 	[   61.427843] Call Trace:
> > 	[   61.427843]  [<ffffffff803332e1>] _raw_spin_lock+0xe9/0x12a
> > 	[   61.427843]  [<ffffffff80324ccf>] as_merged_requests+0xfe/0x115
> > 	[   61.427843]  [<ffffffff8031b558>] elv_merge_requests+0x1f/0x45
> > 	[   61.427843]  [<ffffffff8031e6f7>] attempt_merge+0x281/0x347
> > 	[   61.427843]  [<ffffffff8031f153>] __make_request+0x1e6/0x598
> > 	[   61.427843]  [<ffffffff8031d6ea>] generic_make_request+0x1c8/0x276
> > 	[   61.427843]  [<ffffffff8031d7f9>] submit_bio+0x61/0xdb
> > 	[   61.427843]  [<ffffffff8029b0d2>] submit_bh+0xe2/0x118
> > 	[   61.427843]  [<ffffffff802f69f3>] journal_do_submit_data+0x28/0x39
> > 	[   61.427843]  [<ffffffff802f77da>] journal_commit_transaction+0xdbe/0x1394
> > 	[   61.427843]  [<ffffffff802381a8>] lock_timer_base+0x26/0x4e
> > 	[   61.427843]  [<ffffffff802fb85f>] kjournald+0x104/0x373
> > 	[   61.427843]  [<ffffffff80242087>] autoremove_wake_function+0x0/0x2e
> > 	[   61.427843]  [<ffffffff802fb75b>] kjournald+0x0/0x373
> > 	[   61.427843]  [<ffffffff80241cd4>] kthread+0x3d/0x61
> > 	[   61.427843]  [<ffffffff8020c0e8>] child_rip+0xa/0x12
> > 	[   61.427843]  [<ffffffff80241c97>] kthread+0x0/0x61
> > 	[   61.427843]  [<ffffffff8020c0de>] child_rip+0x0/0x12
> 
> Ah crap, I see the problem, nioc is most often equal to rioc. Dang.
> Please try this bandaid, will push a real fix now.

This is way cleaner.

diff --git a/block/as-iosched.c b/block/as-iosched.c
index b201d16..9603684 100644
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -1275,9 +1275,13 @@ static void as_merged_requests(struct request_queue *q, struct request *req,
 			 * Don't copy here but swap, because when anext is
 			 * removed below, it must contain the unused context
 			 */
-			double_spin_lock(&rioc->lock, &nioc->lock, rioc < nioc);
-			swap_io_context(&rioc, &nioc);
-			double_spin_unlock(&rioc->lock, &nioc->lock, rioc < nioc);
+			if (rioc != nioc) {
+				double_spin_lock(&rioc->lock, &nioc->lock,
+								rioc < nioc);
+				swap_io_context(&rioc, &nioc);
+				double_spin_unlock(&rioc->lock, &nioc->lock,
+								rioc < nioc);
+			}
 		}
 	}
 

-- 
Jens Axboe