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SubjectRe: [PATCH v4 03/12] ext2, dax: finish implementing dax_sem helpers
On Mon 26-02-18 20:20:11, Dan Williams wrote:
> dax_sem_{up,down}_write_sem() allow the ext2 dax semaphore to be compiled
> out in the CONFIG_FS_DAX=n case. However there are still some open coded
> uses of the semaphore. Add dax_sem_{up_read,down_read,_is_locked}()
> helpers and convert all open-coded usages of the semaphore to the
> helpers.

Just one nit below. With that fixed you can add:

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

> Cc: Jan Kara <jack@suse.com>
> Cc: <stable@vger.kernel.org>
> Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap")
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> fs/ext2/ext2.h | 6 ++++++
> fs/ext2/file.c | 5 ++---
> fs/ext2/inode.c | 4 +---
> 3 files changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ext2/ext2.h b/fs/ext2/ext2.h
> index 032295e1d386..7ceb29733cdb 100644
> --- a/fs/ext2/ext2.h
> +++ b/fs/ext2/ext2.h
> @@ -711,9 +711,15 @@ struct ext2_inode_info {
> #ifdef CONFIG_FS_DAX
> #define dax_sem_down_write(ext2_inode) down_write(&(ext2_inode)->dax_sem)
> #define dax_sem_up_write(ext2_inode) up_write(&(ext2_inode)->dax_sem)
> +#define dax_sem_is_locked(ext2_inode) rwsem_is_locked(&(ext2_inode)->dax_sem)
> +#define dax_sem_down_read(ext2_inode) down_read(&(ext2_inode)->dax_sem)
> +#define dax_sem_up_read(ext2_inode) up_read(&(ext2_inode)->dax_sem)
> #else
> #define dax_sem_down_write(ext2_inode)
> #define dax_sem_up_write(ext2_inode)
> +#define dax_sem_is_locked(ext2_inode) (true)

This is a bit dangerous as depending on the use of dax_sem_is_locked()
you'd need this to return true or false. E.g. assume we'd have a place
where we'd like to do:

WARN_ON(dax_sem_is_locked(inode));

or just

if (dax_sem_is_locked(inode))
bail out due to congestion...

How I'd solve this is that I'd define:

#define assert_dax_sem_locked(ext2_inode) WARN_ON(rwsem_is_locked(&(ext2_inode)->dax_sem)

and just as do {} while (0) for !CONFIG_FS_DAX.

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR

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