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Date: Mon, 13 Jan 2020 14:19:57 -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: [RFC PATCH V2 08/12] fs/xfs: Add lock/unlock mode to xfs
On Fri, Jan 10, 2020 at 11:29:38AM -0800, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
>
> XFS requires regular files to be locked while changing to/from DAX mode.
>
> Define a new DAX lock type and implement the [un]lock_mode() inode
> operation callbacks.
>
> We define a new XFS_DAX_* lock type to carry the lock through the
> transaction because we don't want to use IOLOCK as that would cause
> performance issues with locking of the inode itself.
>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> ---
> fs/xfs/xfs_icache.c | 2 ++
> fs/xfs/xfs_inode.c | 37 +++++++++++++++++++++++++++++++++++--
> fs/xfs/xfs_inode.h | 12 ++++++++++--
> fs/xfs/xfs_iops.c | 24 +++++++++++++++++++++++-
> 4 files changed, 70 insertions(+), 5 deletions(-)
>
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index 8dc2e5414276..0288672e8902 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -74,6 +74,8 @@ xfs_inode_alloc(
> INIT_LIST_HEAD(&ip->i_ioend_list);
> spin_lock_init(&ip->i_ioend_lock);
>
> + percpu_init_rwsem(&ip->i_dax_sem);
> +
> return ip;
> }
>
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 401da197f012..e8fd95b75e5b 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
> + * i_rwsem -> i_dax_sem -> i_mmap_lock -> page_lock -> i_ilock
Mmmmmm, more locks. Can we skip the extra lock if CONFIG_FSDAX=n or if
the filesystem devices don't support DAX at all?
Also, I don't think we're actually following the i_rwsem -> i_daxsem
order in fallocate, and possibly elsewhere too?
Does the vfs have to take the i_dax_sem to do remapping things like
reflink? (Pretend that reflink and dax are compatible for the moment)
> * mmap_sem locking order:
> *
> * i_rwsem -> page lock -> mmap_sem
> - * mmap_sem -> i_mmap_lock -> page_lock
> + * mmap_sem -> i_dax_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
> @@ -181,6 +181,13 @@ xfs_ilock(
> 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_SHARED | XFS_DAX_EXCL)) !=
> + (XFS_DAX_SHARED | XFS_DAX_EXCL));
> +
> + if (lock_flags & XFS_DAX_EXCL)
> + percpu_down_write(&ip->i_dax_sem);
> + else if (lock_flags & XFS_DAX_SHARED)
> + percpu_down_read(&ip->i_dax_sem);
>
> if (lock_flags & XFS_IOLOCK_EXCL) {
> down_write_nested(&VFS_I(ip)->i_rwsem,
> @@ -224,6 +231,8 @@ 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 +241,7 @@ 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_SHARED | XFS_DAX_EXCL)) == 0);
>
> if (lock_flags & XFS_IOLOCK_EXCL) {
> if (!down_write_trylock(&VFS_I(ip)->i_rwsem))
> @@ -302,6 +312,8 @@ xfs_iunlock(
> (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
> ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_SUBCLASS_MASK)) == 0);
> ASSERT(lock_flags != 0);
> + ASSERT((lock_flags & (XFS_DAX_SHARED | XFS_DAX_EXCL)) !=
> + (XFS_DAX_SHARED | XFS_DAX_EXCL));
>
> if (lock_flags & XFS_IOLOCK_EXCL)
> up_write(&VFS_I(ip)->i_rwsem);
> @@ -318,6 +330,11 @@ xfs_iunlock(
> else if (lock_flags & XFS_ILOCK_SHARED)
> mrunlock_shared(&ip->i_lock);
>
> + if (lock_flags & XFS_DAX_EXCL)
> + percpu_up_write(&ip->i_dax_sem);
> + else if (lock_flags & XFS_DAX_SHARED)
> + percpu_up_read(&ip->i_dax_sem);
> +
> trace_xfs_iunlock(ip, lock_flags, _RET_IP_);
> }
>
> @@ -333,6 +350,8 @@ 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_SHARED | XFS_DAX_EXCL)) == 0);
>
> if (lock_flags & XFS_ILOCK_EXCL)
> mrdemote(&ip->i_lock);
> @@ -369,6 +388,13 @@ xfs_isilocked(
> return rwsem_is_locked(&VFS_I(ip)->i_rwsem);
> }
>
> + if (lock_flags & (XFS_DAX_EXCL|XFS_DAX_SHARED)) {
> + if (!(lock_flags & XFS_DAX_SHARED))
> + return !debug_locks ||
> + percpu_rwsem_is_held(&ip->i_dax_sem, 0);
> + return rwsem_is_locked(&ip->i_dax_sem);
> + }
> +
> ASSERT(0);
> return 0;
> }
> @@ -465,6 +491,9 @@ 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_SHARED | 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 +595,10 @@ 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_SHARED | XFS_DAX_EXCL)) == 0);
> + ASSERT((ip1_mode & (XFS_DAX_SHARED | 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..693ca66bd89b 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -67,6 +67,9 @@ typedef struct xfs_inode {
> spinlock_t i_ioend_lock;
> struct work_struct i_ioend_work;
> struct list_head i_ioend_list;
> +
> + /* protect changing the mode to/from DAX */
> + struct percpu_rw_semaphore i_dax_sem;
> } xfs_inode_t;
>
> /* Convert from vfs inode to xfs inode */
> @@ -278,10 +281,13 @@ 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_DAX_SHARED (1<<7)
>
> #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 | XFS_DAX_SHARED)
>
> #define XFS_LOCK_FLAGS \
> { XFS_IOLOCK_EXCL, "IOLOCK_EXCL" }, \
> @@ -289,7 +295,9 @@ 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" }, \
Whitespace between the comma & string.
> + { XFS_DAX_SHARED, "DAX_SHARED" }
>
>
> /*
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index d6843cdb51d0..a2f2604c3187 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1158,6 +1158,16 @@ xfs_vn_tmpfile(
> return xfs_generic_create(dir, dentry, mode, 0, true);
> }
>
> +static void xfs_lock_mode(struct inode *inode)
> +{
> + xfs_ilock(XFS_I(inode), XFS_DAX_SHARED);
> +}
> +
> +static void xfs_unlock_mode(struct inode *inode)
> +{
> + xfs_iunlock(XFS_I(inode), XFS_DAX_SHARED);
> +}
> +
> static const struct inode_operations xfs_inode_operations = {
> .get_acl = xfs_get_acl,
> .set_acl = xfs_set_acl,
> @@ -1168,6 +1178,18 @@ static const struct inode_operations xfs_inode_operations = {
> .update_time = xfs_vn_update_time,
> };
>
> +static const struct inode_operations xfs_reg_inode_operations = {
> + .get_acl = xfs_get_acl,
> + .set_acl = xfs_set_acl,
> + .getattr = xfs_vn_getattr,
> + .setattr = xfs_vn_setattr,
> + .listxattr = xfs_vn_listxattr,
> + .fiemap = xfs_vn_fiemap,
> + .update_time = xfs_vn_update_time,
> + .lock_mode = xfs_lock_mode,
> + .unlock_mode = xfs_unlock_mode,
> +};
> +
> static const struct inode_operations xfs_dir_inode_operations = {
> .create = xfs_vn_create,
> .lookup = xfs_vn_lookup,
> @@ -1372,7 +1394,7 @@ xfs_setup_iops(
>
> switch (inode->i_mode & S_IFMT) {
> case S_IFREG:
> - inode->i_op = &xfs_inode_operations;
> + inode->i_op = &xfs_reg_inode_operations;
xfs_file_inode_operations?
--D
> inode->i_fop = &xfs_file_operations;
> if (IS_DAX(inode))
> inode->i_mapping->a_ops = &xfs_dax_aops;
> --
> 2.21.0
>
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