linux-kernel - Re: [PATCH 0/4] kill-the-bkl/reiserfs: fix some lock dependency inversions

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Date:	Thu, 17 Sep 2009 03:37:22 +0400
From:	Alexander Beregalov <a.beregalov@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Reiserfs <reiserfs-devel@...r.kernel.org>
Subject: Re: [PATCH 0/4] kill-the-bkl/reiserfs: fix some lock dependency 
	inversions

2009/9/17 Frederic Weisbecker <fweisbec@...il.com>:
> On Tue, Sep 15, 2009 at 01:33:42AM +0400, Alexander Beregalov wrote:
>> > Hi Alexander,
>> >
>> > It should be fixed now, still in the following tree:
>>
>> Hi!
>> Another one, similar:
>> It is v2.6.31-3123-g99bc470 plus your 805031859(kill-the-bkl/reiserfs:
>> panic in case of lock imbalance), UP.
>
>
>
> Although I can't reproduce it, I think I see how that can happen.
>
> On mount time, we have the following dependency:
>
> reiserfs_lock -> bdev_mutex -> sysfs_mutex
>
> which happens while calling journal_init_dev() because
> we open the device there.
>
> But also in case of mmap on a reiserfs filesystem we
> may call reiserfs_readpages(), holding the reiserfs lock
> while already holding mm->mmap_sem
>
> The above dependency is then updated:
>
> mmap_sem
>     |
>     |
>     ------- reiserfs_lock -> bdev_mutex -> sysfs_mutex
>
> And later, while doing a readdir() on a sysfs directory,
> sysfs calls filldir, which might_fault, and then might grab
> mmap_sem. filldir is called there while holding sys_mutex,
> creating the new following dependency
>
> sysfs_mutex -> mmap_sem
>
> Hence the inversion.
> It seems the deadlock can't ever happen, I even don't see
> corner cases where it could happen.
>
> But still, this dependency should disappear.
>
> Could you please tell me if the following patch makes it shut down?
>
> Otherwise, I may need your config. I don't know why, but I suspect
> the lock_acquire(mmap_sem) in might_fault doesn't trigger needed the lockdep
> check, although I have the appropriate debug config, at least it seems.
> But anyway, it should also happen in my box but it doesn't...
>
> Thanks!
>
> The patch:
Yes, it is working!

>
> diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c
> index d23d6d7..59f7a4c 100644
> --- a/fs/reiserfs/journal.c
> +++ b/fs/reiserfs/journal.c
> @@ -2801,11 +2801,14 @@ int journal_init(struct super_block *sb, const char *j_dev_name,
>                goto free_and_return;
>        }
>
> +       reiserfs_write_unlock(sb);
>        if (journal_init_dev(sb, journal, j_dev_name) != 0) {
>                reiserfs_warning(sb, "sh-462",
>                                 "unable to initialize jornal device");
> +               reiserfs_write_lock(sb);
>                goto free_and_return;
>        }
> +       reiserfs_write_lock(sb);
>
>        rs = SB_DISK_SUPER_BLOCK(sb);
>
>
>
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