linux-kernel - Re: [PATCH V4 09/13] fs/xfs: Add write aops lock to xfs layer

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Date:   Fri, 21 Feb 2020 16:31:09 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     ira.weiny@...el.com
Cc:     linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V4 09/13] fs/xfs: Add write aops lock to xfs layer

On Thu, Feb 20, 2020 at 04:41:30PM -0800, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> XFS requires the use of the aops of an inode to quiesced prior to
> changing it to/from the DAX aops vector.
> 
> Take the aops write lock while changing DAX state.
> 
> We define a new XFS_DAX_EXCL lock type to carry the lock through to
> transaction completion.
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> 
> ---
> Changes from v3:
> 	Change locking function names to reflect changes in previous
> 	patches.
> 
> Changes from V2:
> 	Change name of patch (WAS: fs/xfs: Add lock/unlock state to xfs)
> 	Remove the xfs specific lock and move to the vfs layer.
> 		We still use XFS_LOCK_DAX_EXCL to be able to pass this
> 		flag through to the transaction code.  But we no longer
> 		have a lock specific to xfs.  This removes a lot of code
> 		from the XFS layer, preps us for using this in ext4, and
> 		is actually more straight forward now that all the
> 		locking requirements are better known.
> 
> 	Fix locking order comment
> 	Rework for new 'state' names
> 	(Other comments on the previous patch are not applicable with
> 	new patch as much of the code was removed in favor of the vfs
> 	level lock)
> ---
>  fs/xfs/xfs_inode.c | 22 ++++++++++++++++++++--
>  fs/xfs/xfs_inode.h |  7 +++++--
>  2 files changed, 25 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 35df324875db..5b014c428f0f 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -142,12 +142,12 @@ xfs_ilock_attr_map_shared(
>   *
>   * Basic locking order:
>   *
> - * i_rwsem -> i_mmap_lock -> page_lock -> i_ilock
> + * s_dax_sem -> i_rwsem -> i_mmap_lock -> page_lock -> i_ilock

"dax_sem"?  I thought this was now called i_aops_sem?

>   *
>   * mmap_sem locking order:
>   *
>   * i_rwsem -> page lock -> mmap_sem
> - * mmap_sem -> i_mmap_lock -> page_lock
> + * s_dax_sem -> mmap_sem -> i_mmap_lock -> page_lock
>   *
>   * The difference in mmap_sem locking order mean that we cannot hold the
>   * i_mmap_lock over syscall based read(2)/write(2) based IO. These IO paths can
> @@ -182,6 +182,9 @@ xfs_ilock(
>  	       (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
>  	ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_SUBCLASS_MASK)) == 0);
>  
> +	if (lock_flags & XFS_DAX_EXCL)

And similarly, I think this should be XFS_OPSLOCK_EXCL...

--D

> +		inode_aops_down_write(VFS_I(ip));
> +
>  	if (lock_flags & XFS_IOLOCK_EXCL) {
>  		down_write_nested(&VFS_I(ip)->i_rwsem,
>  				  XFS_IOLOCK_DEP(lock_flags));
> @@ -224,6 +227,8 @@ xfs_ilock_nowait(
>  	 * You can't set both SHARED and EXCL for the same lock,
>  	 * and only XFS_IOLOCK_SHARED, XFS_IOLOCK_EXCL, XFS_ILOCK_SHARED,
>  	 * and XFS_ILOCK_EXCL are valid values to set in lock_flags.
> +	 *
> +	 * XFS_DAX_* is not allowed
>  	 */
>  	ASSERT((lock_flags & (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL)) !=
>  	       (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL));
> @@ -232,6 +237,7 @@ xfs_ilock_nowait(
>  	ASSERT((lock_flags & (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL)) !=
>  	       (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
>  	ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_SUBCLASS_MASK)) == 0);
> +	ASSERT((lock_flags & XFS_DAX_EXCL) == 0);
>  
>  	if (lock_flags & XFS_IOLOCK_EXCL) {
>  		if (!down_write_trylock(&VFS_I(ip)->i_rwsem))
> @@ -318,6 +324,9 @@ xfs_iunlock(
>  	else if (lock_flags & XFS_ILOCK_SHARED)
>  		mrunlock_shared(&ip->i_lock);
>  
> +	if (lock_flags & XFS_DAX_EXCL)
> +		inode_aops_up_write(VFS_I(ip));
> +
>  	trace_xfs_iunlock(ip, lock_flags, _RET_IP_);
>  }
>  
> @@ -333,6 +342,8 @@ xfs_ilock_demote(
>  	ASSERT(lock_flags & (XFS_IOLOCK_EXCL|XFS_MMAPLOCK_EXCL|XFS_ILOCK_EXCL));
>  	ASSERT((lock_flags &
>  		~(XFS_IOLOCK_EXCL|XFS_MMAPLOCK_EXCL|XFS_ILOCK_EXCL)) == 0);
> +	/* XFS_DAX_* is not allowed */
> +	ASSERT((lock_flags & XFS_DAX_EXCL) == 0);
>  
>  	if (lock_flags & XFS_ILOCK_EXCL)
>  		mrdemote(&ip->i_lock);
> @@ -465,6 +476,9 @@ xfs_lock_inodes(
>  	ASSERT(!(lock_mode & XFS_ILOCK_EXCL) ||
>  		inodes <= XFS_ILOCK_MAX_SUBCLASS + 1);
>  
> +	/* XFS_DAX_* is not allowed */
> +	ASSERT((lock_mode & XFS_DAX_EXCL) == 0);
> +
>  	if (lock_mode & XFS_IOLOCK_EXCL) {
>  		ASSERT(!(lock_mode & (XFS_MMAPLOCK_EXCL | XFS_ILOCK_EXCL)));
>  	} else if (lock_mode & XFS_MMAPLOCK_EXCL)
> @@ -566,6 +580,10 @@ xfs_lock_two_inodes(
>  	ASSERT(!(ip0_mode & (XFS_MMAPLOCK_SHARED|XFS_MMAPLOCK_EXCL)) ||
>  	       !(ip1_mode & (XFS_ILOCK_SHARED|XFS_ILOCK_EXCL)));
>  
> +	/* XFS_DAX_* is not allowed */
> +	ASSERT((ip0_mode & XFS_DAX_EXCL) == 0);
> +	ASSERT((ip1_mode & XFS_DAX_EXCL) == 0);
> +
>  	ASSERT(ip0->i_ino != ip1->i_ino);
>  
>  	if (ip0->i_ino > ip1->i_ino) {
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index 492e53992fa9..25fe20740bf7 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -278,10 +278,12 @@ static inline void xfs_ifunlock(struct xfs_inode *ip)
>  #define	XFS_ILOCK_SHARED	(1<<3)
>  #define	XFS_MMAPLOCK_EXCL	(1<<4)
>  #define	XFS_MMAPLOCK_SHARED	(1<<5)
> +#define	XFS_DAX_EXCL		(1<<6)
>  
>  #define XFS_LOCK_MASK		(XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED \
>  				| XFS_ILOCK_EXCL | XFS_ILOCK_SHARED \
> -				| XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED)
> +				| XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED \
> +				| XFS_DAX_EXCL)
>  
>  #define XFS_LOCK_FLAGS \
>  	{ XFS_IOLOCK_EXCL,	"IOLOCK_EXCL" }, \
> @@ -289,7 +291,8 @@ static inline void xfs_ifunlock(struct xfs_inode *ip)
>  	{ XFS_ILOCK_EXCL,	"ILOCK_EXCL" }, \
>  	{ XFS_ILOCK_SHARED,	"ILOCK_SHARED" }, \
>  	{ XFS_MMAPLOCK_EXCL,	"MMAPLOCK_EXCL" }, \
> -	{ XFS_MMAPLOCK_SHARED,	"MMAPLOCK_SHARED" }
> +	{ XFS_MMAPLOCK_SHARED,	"MMAPLOCK_SHARED" }, \
> +	{ XFS_DAX_EXCL,		"DAX_EXCL" }
>  
>  
>  /*
> -- 
> 2.21.0
>