linux-ext4 - Re: (un)lock

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Message-ID: <alpine.DEB.0.83.0704041244560.4770@sigma.j-a-k-j.com>
Date:	Wed, 4 Apr 2007 12:52:07 -0400 (EDT)
From:	"John Anthony Kazos Jr." <jakj@...-k-j.com>
To:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
cc:	linux-ext4@...r.kernel.org
Subject: Re: (un)lock_kernel() ?

> According to Documentation/filesystems/Locking, ->get_sb() is called
> with the BKL held, but looking through the code, I'm not able to find
> where it is being taken.

I noticed that too. Unless I'm just dumb and can't see it, I'm not able to 
find any BKL references during filesystem mounting until you get into 
FS-specific code. I looked through everything from sys_mount through to 
vfs_kern_mount. Documentation/filesystems/porting talks about several 
situations where the VFS code was modified to not take the BKL, and BLK 
calls were added by FS non-maintainers for safety until each FS could be 
audited independently, but that wouldn't be the case, would it?

The ext2 code takes the BKL in three places: ext2_update_inode, 
write_super, and ext2_compat_ioctl. Starting with ext3, it's in 
ext3_compat_ioctl and ext3_fill_super, and the same with ext4.

I suppose the BKL does have to be held, somehow, somewhere, during 
mounting, or anybody using ext3 on a multiprocessor box would lock their 
system from unmatched locking calls. Unless the first unlock_kernel() 
would make the count -1 and the lock would bring it back to zero?
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