linux-kernel - Re: [PATCH] locks: fix F_GETLK regression (failure to find conflicts)

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Message-Id: <1178839856.21710.0.camel@phobos>
Date:	Thu, 10 May 2007 19:30:56 -0400
From:	Doug Chapman <doug.chapman@...com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	Marc Eshel <eshel@...aden.ibm.com>,
	Trond Myklebust <trond@...app.com>
Subject: Re: [PATCH] locks: fix F_GETLK regression (failure to find
	conflicts)

On Thu, 2007-05-10 at 18:38 -0400, J. Bruce Fields wrote:
> In 9d6a8c5c213e34c475e72b245a8eb709258e968c we changed posix_test_lock
> to modify its single file_lock argument instead of taking separate input
> and output arguments.  This makes it no longer safe to set the output
> lock's fl_type to F_UNLCK before looking for a conflict, since that
> means searching for a conflict against a lock with type F_UNLCK.
> 
> This fixes a regression which causes F_GETLK to incorrectly report no
> conflict on most filesystems (including any filesystem that doesn't do
> its own locking).
> 
> Also fix posix_lock_to_flock() to copy the lock type.  This isn't
> strictly necessary, since the caller already does this; but it seems
> less likely to cause confusion in the future.
> 
> Thanks to Doug Chapman for the bug report.
> 
> Signed-off-by: "J. Bruce Fields" <bfields@...i.umich.edu>
> ---
>  fs/locks.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index 671a034..8ec16ab 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -669,7 +669,6 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
>  {
>  	struct file_lock *cfl;
>  
> -	fl->fl_type = F_UNLCK;
>  	lock_kernel();
>  	for (cfl = filp->f_path.dentry->d_inode->i_flock; cfl; cfl = cfl->fl_next) {
>  		if (!IS_POSIX(cfl))
> @@ -681,7 +680,8 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
>  		__locks_copy_lock(fl, cfl);
>  		unlock_kernel();
>  		return 1;
> -	}
> +	} else
> +		fl->fl_type = F_UNLCK;
>  	unlock_kernel();
>  	return 0;
>  }
> @@ -1632,6 +1632,7 @@ static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
>  	flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
>  		fl->fl_end - fl->fl_start + 1;
>  	flock->l_whence = 0;
> +	flock->l_type = fl->fl_type;
>  	return 0;
>  }
>  

I tested this both with my little hacked up test program as well as with
the LTP tests.  Looks good.  Nice job on the quick turnaround on this
Bruce.

- Doug


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