linux-kernel - Re: [PATCH v2 1/5] dax: never rely on bh.b_dev being set by get

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Message-ID: <20160122145345.GJ16898@quack.suse.cz>
Date:	Fri, 22 Jan 2016 15:53:45 +0100
From:	Jan Kara <jack@...e.cz>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-fsdevel@...r.kernel.org, linux-nvdimm@...ts.01.org
Subject: Re: [PATCH v2 1/5] dax: never rely on bh.b_dev being set by
 get_block()

On Thu 21-01-16 10:46:00, Ross Zwisler wrote:
> Previously in DAX we assumed that calls to get_block() would set bh.b_bdev,
> and we would then use that value even in error cases for debugging.  This
> caused a NULL pointer dereference in __dax_dbg() which was fixed by a
> previous commit, but that commit only changed the one place where we were
> hitting an error.
> 
> Instead, update dax.c so that we always initialize bh.b_bdev as best we can
> based on the information that DAX has.  get_block() may or may not update
> to a new value, but this at least lets us get something helpful from
> bh.b_bdev for error messages and not have to worry about whether it was set
> by get_block() or not.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Reported-by: Jan Kara <jack@...e.cz>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/dax.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 0db21ea..cee9e1b 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -246,6 +246,7 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
>  	loff_t end = pos + iov_iter_count(iter);
>  
>  	memset(&bh, 0, sizeof(bh));
> +	bh.b_bdev = inode->i_sb->s_bdev;
>  
>  	if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ) {
>  		struct address_space *mapping = inode->i_mapping;
> @@ -582,6 +583,7 @@ int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
>  
>  	memset(&bh, 0, sizeof(bh));
>  	block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
> +	bh.b_bdev = inode->i_sb->s_bdev;
>  	bh.b_size = PAGE_SIZE;
>  
>   repeat:
> @@ -1018,6 +1020,7 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
>  	BUG_ON((offset + length) > PAGE_CACHE_SIZE);
>  
>  	memset(&bh, 0, sizeof(bh));
> +	bh.b_bdev = inode->i_sb->s_bdev;
>  	bh.b_size = PAGE_CACHE_SIZE;
>  	err = get_block(inode, index, &bh, 0);
>  	if (err < 0)
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR