linux-ext4 - Re: locking typo in ext4_mb_add_n

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Date:	Fri, 27 Mar 2009 09:16:59 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Dan Carpenter <error27@...il.com>
CC:	tytso@....edu, adilger@....com, linux-ext4@...r.kernel.org
Subject: Re: locking typo in ext4_mb_add_n_trim()

Dan Carpenter wrote:
> Smatch (http://repo.or.cz/w/smatch.git/) complains about the locking in 
> ext4_mb_add_n_trim() from fs/ext4/mballoc.c
> 
> I think it's meant to be spin_unlock(&tmp_pa->pa_lock); on line 4442.
> 
>   4438          list_for_each_entry_rcu(tmp_pa, &lg->lg_prealloc_list[order],
>   4439                                                  pa_inode_list) {
>   4440                  spin_lock(&tmp_pa->pa_lock);
>   4441                  if (tmp_pa->pa_deleted) {
>   4442                          spin_unlock(&pa->pa_lock);
>   4443                          continue;
>   4444                  }
> 
> I can send a patch if I'm right or you could just give me a:
> Reported-by: Dan Carpenter <error27@...il.com>

Seems right to me,

Reviewed-by: Eric Sandeen <sandeen@...hat.com>

although I wonder why we don't trip over this in spinlock debugging
(seems like it'd lead to a double unlock at times)  I wonder if we can
tie this to any other bugs we've seen.

Thanks,
-Eric
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