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Date: Fri, 12 Jan 2024 16:29:30 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: Chandan Babu R <chandan.babu@...cle.com>, linux-kernel@...r.kernel.org,
linux-xfs@...r.kernel.org, Mateusz Guzik <mjguzik@...il.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v5 3/3] xfs: Remove mrlock wrapper
On Thu, Jan 11, 2024 at 09:24:24PM +0000, Matthew Wilcox (Oracle) wrote:
> mrlock was an rwsem wrapper that also recorded whether the lock was
> held for read or write. Now that we can ask the generic code whether
> the lock is held for read or write, we can remove this wrapper and use
> an rwsem directly.
>
> As the comment says, we can't use lockdep to assert that the ILOCK is
> held for write, because we might be in a workqueue, and we aren't able
> to tell lockdep that we do in fact own the lock.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
> fs/xfs/mrlock.h | 78 ----------------------------------------------
> fs/xfs/xfs_inode.c | 22 +++++++------
> fs/xfs/xfs_inode.h | 2 +-
> fs/xfs/xfs_iops.c | 4 +--
> fs/xfs/xfs_linux.h | 2 +-
> fs/xfs/xfs_super.c | 4 +--
> 6 files changed, 18 insertions(+), 94 deletions(-)
> delete mode 100644 fs/xfs/mrlock.h
>
> diff --git a/fs/xfs/mrlock.h b/fs/xfs/mrlock.h
> deleted file mode 100644
> index 79155eec341b..000000000000
> --- a/fs/xfs/mrlock.h
> +++ /dev/null
> @@ -1,78 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0
> -/*
> - * Copyright (c) 2000-2006 Silicon Graphics, Inc.
> - * All Rights Reserved.
> - */
> -#ifndef __XFS_SUPPORT_MRLOCK_H__
> -#define __XFS_SUPPORT_MRLOCK_H__
> -
> -#include <linux/rwsem.h>
> -
> -typedef struct {
> - struct rw_semaphore mr_lock;
> -#if defined(DEBUG) || defined(XFS_WARN)
> - int mr_writer;
> -#endif
> -} mrlock_t;
> -
> -#if defined(DEBUG) || defined(XFS_WARN)
> -#define mrinit(mrp, name) \
> - do { (mrp)->mr_writer = 0; init_rwsem(&(mrp)->mr_lock); } while (0)
> -#else
> -#define mrinit(mrp, name) \
> - do { init_rwsem(&(mrp)->mr_lock); } while (0)
> -#endif
> -
> -#define mrlock_init(mrp, t,n,s) mrinit(mrp, n)
> -#define mrfree(mrp) do { } while (0)
> -
> -static inline void mraccess_nested(mrlock_t *mrp, int subclass)
> -{
> - down_read_nested(&mrp->mr_lock, subclass);
> -}
> -
> -static inline void mrupdate_nested(mrlock_t *mrp, int subclass)
> -{
> - down_write_nested(&mrp->mr_lock, subclass);
> -#if defined(DEBUG) || defined(XFS_WARN)
> - mrp->mr_writer = 1;
> -#endif
> -}
> -
> -static inline int mrtryaccess(mrlock_t *mrp)
> -{
> - return down_read_trylock(&mrp->mr_lock);
> -}
> -
> -static inline int mrtryupdate(mrlock_t *mrp)
> -{
> - if (!down_write_trylock(&mrp->mr_lock))
> - return 0;
> -#if defined(DEBUG) || defined(XFS_WARN)
> - mrp->mr_writer = 1;
> -#endif
> - return 1;
> -}
> -
> -static inline void mrunlock_excl(mrlock_t *mrp)
> -{
> -#if defined(DEBUG) || defined(XFS_WARN)
> - mrp->mr_writer = 0;
> -#endif
> - up_write(&mrp->mr_lock);
> -}
> -
> -static inline void mrunlock_shared(mrlock_t *mrp)
> -{
> - up_read(&mrp->mr_lock);
> -}
> -
> -static inline void mrdemote(mrlock_t *mrp)
> -{
> -#if defined(DEBUG) || defined(XFS_WARN)
> - mrp->mr_writer = 0;
> -#endif
> - downgrade_write(&mrp->mr_lock);
> -}
> -
> -#endif /* __XFS_SUPPORT_MRLOCK_H__ */
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 728b3bc1c3db..b9b2af913e89 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -203,9 +203,9 @@ xfs_ilock(
> }
>
> if (lock_flags & XFS_ILOCK_EXCL)
> - mrupdate_nested(&ip->i_lock, XFS_ILOCK_DEP(lock_flags));
> + down_write_nested(&ip->i_lock, XFS_ILOCK_DEP(lock_flags));
> else if (lock_flags & XFS_ILOCK_SHARED)
> - mraccess_nested(&ip->i_lock, XFS_ILOCK_DEP(lock_flags));
> + down_read_nested(&ip->i_lock, XFS_ILOCK_DEP(lock_flags));
> }
>
> /*
> @@ -246,10 +246,10 @@ xfs_ilock_nowait(
> }
>
> if (lock_flags & XFS_ILOCK_EXCL) {
> - if (!mrtryupdate(&ip->i_lock))
> + if (!down_write_trylock(&ip->i_lock))
> goto out_undo_mmaplock;
> } else if (lock_flags & XFS_ILOCK_SHARED) {
> - if (!mrtryaccess(&ip->i_lock))
> + if (!down_read_trylock(&ip->i_lock))
> goto out_undo_mmaplock;
> }
> return 1;
> @@ -298,9 +298,9 @@ xfs_iunlock(
> up_read(&VFS_I(ip)->i_mapping->invalidate_lock);
>
> if (lock_flags & XFS_ILOCK_EXCL)
> - mrunlock_excl(&ip->i_lock);
> + up_write(&ip->i_lock);
> else if (lock_flags & XFS_ILOCK_SHARED)
> - mrunlock_shared(&ip->i_lock);
> + up_read(&ip->i_lock);
>
> trace_xfs_iunlock(ip, lock_flags, _RET_IP_);
> }
> @@ -319,7 +319,7 @@ xfs_ilock_demote(
> ~(XFS_IOLOCK_EXCL|XFS_MMAPLOCK_EXCL|XFS_ILOCK_EXCL)) == 0);
>
> if (lock_flags & XFS_ILOCK_EXCL)
> - mrdemote(&ip->i_lock);
> + downgrade_write(&ip->i_lock);
> if (lock_flags & XFS_MMAPLOCK_EXCL)
> downgrade_write(&VFS_I(ip)->i_mapping->invalidate_lock);
> if (lock_flags & XFS_IOLOCK_EXCL)
> @@ -333,10 +333,14 @@ xfs_assert_ilocked(
> struct xfs_inode *ip,
> uint lock_flags)
> {
> + /*
> + * Sometimes we assert the ILOCK is held exclusively, but we're in
> + * a workqueue, so lockdep doesn't know we're the owner.
> + */
> if (lock_flags & XFS_ILOCK_SHARED)
> - rwsem_assert_held(&ip->i_lock.mr_lock);
> + rwsem_assert_held(&ip->i_lock);
> else if (lock_flags & XFS_ILOCK_EXCL)
> - ASSERT(ip->i_lock.mr_writer);
> + rwsem_assert_held_write_nolockdep(&ip->i_lock);
Hooray, someone finally broke the gordian knot!
Reviewed-by: Darrick J. Wong <djwong@...nel.org>
--D
>
> if (lock_flags & XFS_MMAPLOCK_SHARED)
> rwsem_assert_held(&VFS_I(ip)->i_mapping->invalidate_lock);
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index dcc818901a79..796d11065fe2 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -39,7 +39,7 @@ typedef struct xfs_inode {
>
> /* Transaction and locking information. */
> struct xfs_inode_log_item *i_itemp; /* logging information */
> - mrlock_t i_lock; /* inode lock */
> + struct rw_semaphore i_lock; /* inode lock */
> atomic_t i_pincount; /* inode pin count */
> struct llist_node i_gclist; /* deferred inactivation list */
>
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index e7fca1913175..73f46486c252 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1284,9 +1284,9 @@ xfs_setup_inode(
> */
> lockdep_set_class(&inode->i_rwsem,
> &inode->i_sb->s_type->i_mutex_dir_key);
> - lockdep_set_class(&ip->i_lock.mr_lock, &xfs_dir_ilock_class);
> + lockdep_set_class(&ip->i_lock, &xfs_dir_ilock_class);
> } else {
> - lockdep_set_class(&ip->i_lock.mr_lock, &xfs_nondir_ilock_class);
> + lockdep_set_class(&ip->i_lock, &xfs_nondir_ilock_class);
> }
>
> /*
> diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
> index d7873e0360f0..ec3c6c138a63 100644
> --- a/fs/xfs/xfs_linux.h
> +++ b/fs/xfs/xfs_linux.h
> @@ -22,7 +22,6 @@ typedef __u32 xfs_nlink_t;
> #include "xfs_types.h"
>
> #include "kmem.h"
> -#include "mrlock.h"
>
> #include <linux/semaphore.h>
> #include <linux/mm.h>
> @@ -51,6 +50,7 @@ typedef __u32 xfs_nlink_t;
> #include <linux/notifier.h>
> #include <linux/delay.h>
> #include <linux/log2.h>
> +#include <linux/rwsem.h>
> #include <linux/spinlock.h>
> #include <linux/random.h>
> #include <linux/ctype.h>
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index aff20ddd4a9f..15831c53a83b 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -716,9 +716,7 @@ xfs_fs_inode_init_once(
> /* xfs inode */
> atomic_set(&ip->i_pincount, 0);
> spin_lock_init(&ip->i_flags_lock);
> -
> - mrlock_init(&ip->i_lock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER,
> - "xfsino", ip->i_ino);
> + init_rwsem(&ip->i_lock);
> }
>
> /*
> --
> 2.43.0
>
>
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