From: Brian Foster <bfoster@redhat.com>
To: Pavel Reichl <preichl@redhat.com>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH v12 4/4] xfs: replace mrlock_t with rw_semaphores
Date: Tue, 20 Oct 2020 06:28:13 -0400 [thread overview]
Message-ID: <20201020102813.GB1263949@bfoster> (raw)
In-Reply-To: <20201016021005.548850-5-preichl@redhat.com>
On Fri, Oct 16, 2020 at 04:10:05AM +0200, Pavel Reichl wrote:
> Remove mrlock_t as it does not provide any extra value over
> rw_semaphores. Make i_lock and i_mmaplock native rw_semaphores and
> replace mr*() functions with native rwsem calls.
>
> Release the lock in xfs_btree_split() just before the work-queue
> executing xfs_btree_split_worker() is scheduled and make
> xfs_btree_split_worker() to acquire the lock as a first thing and
> release it just before returning from the function. This it done so the
> ownership of the lock is transfered between kernel threads and thus
> lockdep won't complain about lock being held by a different kernel
> thread.
>
> Signed-off-by: Pavel Reichl <preichl@redhat.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
> fs/xfs/libxfs/xfs_btree.c | 25 +++++++++++++
> fs/xfs/mrlock.h | 78 ---------------------------------------
> fs/xfs/xfs_inode.c | 52 ++++++++++++++------------
> fs/xfs/xfs_inode.h | 4 +-
> fs/xfs/xfs_iops.c | 4 +-
> fs/xfs/xfs_linux.h | 2 +-
> fs/xfs/xfs_super.c | 6 +--
> 7 files changed, 60 insertions(+), 111 deletions(-)
> delete mode 100644 fs/xfs/mrlock.h
>
> diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
> index 2d25bab68764..5ec2098c271c 100644
> --- a/fs/xfs/libxfs/xfs_btree.c
> +++ b/fs/xfs/libxfs/xfs_btree.c
...
> @@ -2863,8 +2875,21 @@ xfs_btree_split(
> args.done = &done;
> args.kswapd = current_is_kswapd();
> INIT_WORK_ONSTACK(&args.work, xfs_btree_split_worker);
> + /*
> + * Update lockdep's ownership information to reflect transfer of the
> + * ilock from the current task to the worker. Otherwise assertions that
> + * the lock is held (such as when logging the inode) might fail due to
> + * incorrect task owner state.
> + */
> + rwsem_release(&cur->bc_ino.ip->i_lock.dep_map, _THIS_IP_);
IMO this one comment is sufficient to document what's happening and why,
and we could drop the remaining multi-line comments associated with each
lockdep state update call. Alternatively, the others could be reduced to
single line comments along the lines of "transfer lock to workqueue
task," etc. That's just my .02 though.
Also, no need to respin this or patch 1 based on my comments alone. I'm
just pointing out a couple nits that the maintainer can choose to tweak
or not at his discretion:
Reviewed-by: Brian Foster <bfoster@redhat.com>
> queue_work(xfs_alloc_wq, &args.work);
> wait_for_completion(&done);
> + /*
> + * Update lockdep's lock ownership information to point to
> + * this thread as the lock owner now that the worker item is
> + * done.
> + */
> + rwsem_acquire(&cur->bc_ino.ip->i_lock.dep_map, 0, 0, _RET_IP_);
> destroy_work_on_stack(&args.work);
> return args.result;
> }
> 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 085927700530..f47202c487e0 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -191,14 +191,15 @@ xfs_ilock(
> }
>
> if (lock_flags & XFS_MMAPLOCK_EXCL)
> - mrupdate_nested(&ip->i_mmaplock, XFS_MMAPLOCK_DEP(lock_flags));
> + down_write_nested(&ip->i_mmaplock,
> + XFS_MMAPLOCK_DEP(lock_flags));
> else if (lock_flags & XFS_MMAPLOCK_SHARED)
> - mraccess_nested(&ip->i_mmaplock, XFS_MMAPLOCK_DEP(lock_flags));
> + down_read_nested(&ip->i_mmaplock, XFS_MMAPLOCK_DEP(lock_flags));
>
> 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));
> }
>
> /*
> @@ -242,27 +243,27 @@ xfs_ilock_nowait(
> }
>
> if (lock_flags & XFS_MMAPLOCK_EXCL) {
> - if (!mrtryupdate(&ip->i_mmaplock))
> + if (!down_write_trylock(&ip->i_mmaplock))
> goto out_undo_iolock;
> } else if (lock_flags & XFS_MMAPLOCK_SHARED) {
> - if (!mrtryaccess(&ip->i_mmaplock))
> + if (!down_read_trylock(&ip->i_mmaplock))
> goto out_undo_iolock;
> }
>
> 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;
>
> out_undo_mmaplock:
> if (lock_flags & XFS_MMAPLOCK_EXCL)
> - mrunlock_excl(&ip->i_mmaplock);
> + up_write(&ip->i_mmaplock);
> else if (lock_flags & XFS_MMAPLOCK_SHARED)
> - mrunlock_shared(&ip->i_mmaplock);
> + up_read(&ip->i_mmaplock);
> out_undo_iolock:
> if (lock_flags & XFS_IOLOCK_EXCL)
> up_write(&VFS_I(ip)->i_rwsem);
> @@ -309,14 +310,14 @@ xfs_iunlock(
> up_read(&VFS_I(ip)->i_rwsem);
>
> if (lock_flags & XFS_MMAPLOCK_EXCL)
> - mrunlock_excl(&ip->i_mmaplock);
> + up_write(&ip->i_mmaplock);
> else if (lock_flags & XFS_MMAPLOCK_SHARED)
> - mrunlock_shared(&ip->i_mmaplock);
> + up_read(&ip->i_mmaplock);
>
> 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_);
> }
> @@ -335,9 +336,9 @@ 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)
> - mrdemote(&ip->i_mmaplock);
> + downgrade_write(&ip->i_mmaplock);
> if (lock_flags & XFS_IOLOCK_EXCL)
> downgrade_write(&VFS_I(ip)->i_rwsem);
>
> @@ -375,19 +376,22 @@ xfs_isilocked(
> struct xfs_inode *ip,
> uint lock_flags)
> {
> - if (lock_flags & (XFS_ILOCK_EXCL|XFS_ILOCK_SHARED)) {
> - if (!(lock_flags & XFS_ILOCK_SHARED))
> - return !!ip->i_lock.mr_writer;
> - return rwsem_is_locked(&ip->i_lock.mr_lock);
> + if (lock_flags & (XFS_ILOCK_EXCL | XFS_ILOCK_SHARED)) {
> + ASSERT(!(lock_flags & ~(XFS_ILOCK_EXCL | XFS_ILOCK_SHARED)));
> + return __xfs_rwsem_islocked(&ip->i_lock, lock_flags,
> + XFS_ILOCK_FLAG_SHIFT);
> }
>
> - if (lock_flags & (XFS_MMAPLOCK_EXCL|XFS_MMAPLOCK_SHARED)) {
> - if (!(lock_flags & XFS_MMAPLOCK_SHARED))
> - return !!ip->i_mmaplock.mr_writer;
> - return rwsem_is_locked(&ip->i_mmaplock.mr_lock);
> + if (lock_flags & (XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED)) {
> + ASSERT(!(lock_flags &
> + ~(XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED)));
> + return __xfs_rwsem_islocked(&ip->i_mmaplock, lock_flags,
> + XFS_MMAPLOCK_FLAG_SHIFT);
> }
>
> if (lock_flags & (XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED)) {
> + ASSERT(!(lock_flags &
> + ~(XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED)));
> return __xfs_rwsem_islocked(&VFS_I(ip)->i_rwsem, lock_flags,
> XFS_IOLOCK_FLAG_SHIFT);
> }
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index 9cecd6c9c90c..413998972b35 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -39,8 +39,8 @@ typedef struct xfs_inode {
>
> /* Transaction and locking information. */
> struct xfs_inode_log_item *i_itemp; /* logging information */
> - mrlock_t i_lock; /* inode lock */
> - mrlock_t i_mmaplock; /* inode mmap IO lock */
> + struct rw_semaphore i_lock; /* inode lock */
> + struct rw_semaphore i_mmaplock; /* inode mmap IO lock */
> atomic_t i_pincount; /* inode pin count */
>
> /*
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 80a13c8561d8..66cca3e599c7 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1336,9 +1336,9 @@ 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 ab737fed7b12..ba37217f86d2 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>
> @@ -61,6 +60,7 @@ typedef __u32 xfs_nlink_t;
> #include <linux/ratelimit.h>
> #include <linux/rhashtable.h>
> #include <linux/xattr.h>
> +#include <linux/rwsem.h>
>
> #include <asm/page.h>
> #include <asm/div64.h>
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 71ac6c1cdc36..00be9cfa29fa 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -708,10 +708,8 @@ xfs_fs_inode_init_once(
> atomic_set(&ip->i_pincount, 0);
> spin_lock_init(&ip->i_flags_lock);
>
> - mrlock_init(&ip->i_mmaplock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER,
> - "xfsino", ip->i_ino);
> - mrlock_init(&ip->i_lock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER,
> - "xfsino", ip->i_ino);
> + init_rwsem(&ip->i_mmaplock);
> + init_rwsem(&ip->i_lock);
> }
>
> /*
> --
> 2.26.2
>
next prev parent reply other threads:[~2020-10-20 10:28 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-16 2:10 [PATCH v12 0/4] xfs: Remove wrappers for some semaphores Pavel Reichl
2020-10-16 2:10 ` [PATCH v12 1/4] xfs: Refactor xfs_isilocked() Pavel Reichl
2020-10-20 10:28 ` Brian Foster
2020-10-16 2:10 ` [PATCH v12 2/4] xfs: clean up whitespace in xfs_isilocked() calls Pavel Reichl
2020-10-16 2:10 ` [PATCH v12 3/4] xfs: xfs_isilocked() can only check a single lock type Pavel Reichl
2020-10-16 2:10 ` [PATCH v12 4/4] xfs: replace mrlock_t with rw_semaphores Pavel Reichl
2020-10-20 10:28 ` Brian Foster [this message]
2020-10-29 22:35 ` Darrick J. Wong
2020-11-02 19:45 ` Pavel Reichl
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