linux/fs/xfs/libxfs/xfs_trans_inode.c
Dave Chinner 1319ebefd6 xfs: add an inode item lock
The inode log item is kind of special in that it can be aggregating
new changes in memory at the same time time existing changes are
being written back to disk. This means there are fields in the log
item that are accessed concurrently from contexts that don't share
any locking at all.

e.g. updating ili_last_fields occurs at flush time under the
ILOCK_EXCL and flush lock at flush time, under the flush lock at IO
completion time, and is read under the ILOCK_EXCL when the inode is
logged.  Hence there is no actual serialisation between reading the
field during logging of the inode in transactions vs clearing the
field in IO completion.

We currently get away with this by the fact that we are only
clearing fields in IO completion, and nothing bad happens if we
accidentally log more of the inode than we actually modify. Worst
case is we consume a tiny bit more memory and log bandwidth.

However, if we want to do more complex state manipulations on the
log item that requires updates at all three of these potential
locations, we need to have some mechanism of serialising those
operations. To do this, introduce a spinlock into the log item to
serialise internal state.

This could be done via the xfs_inode i_flags_lock, but this then
leads to potential lock inversion issues where inode flag updates
need to occur inside locks that best nest inside the inode log item
locks (e.g. marking inodes stale during inode cluster freeing).
Using a separate spinlock avoids these sorts of problems and
simplifies future code.

This does not touch the use of ili_fields in the item formatting
code - that is entirely protected by the ILOCK_EXCL at this point in
time, so it remains untouched.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
2020-07-06 10:46:58 -07:00

157 lines
4.2 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (c) 2000,2005 Silicon Graphics, Inc.
* All Rights Reserved.
*/
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_inode.h"
#include "xfs_trans.h"
#include "xfs_trans_priv.h"
#include "xfs_inode_item.h"
#include <linux/iversion.h>
/*
* Add a locked inode to the transaction.
*
* The inode must be locked, and it cannot be associated with any transaction.
* If lock_flags is non-zero the inode will be unlocked on transaction commit.
*/
void
xfs_trans_ijoin(
struct xfs_trans *tp,
struct xfs_inode *ip,
uint lock_flags)
{
struct xfs_inode_log_item *iip;
ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
if (ip->i_itemp == NULL)
xfs_inode_item_init(ip, ip->i_mount);
iip = ip->i_itemp;
ASSERT(iip->ili_lock_flags == 0);
iip->ili_lock_flags = lock_flags;
ASSERT(!xfs_iflags_test(ip, XFS_ISTALE));
/*
* Get a log_item_desc to point at the new item.
*/
xfs_trans_add_item(tp, &iip->ili_item);
}
/*
* Transactional inode timestamp update. Requires the inode to be locked and
* joined to the transaction supplied. Relies on the transaction subsystem to
* track dirty state and update/writeback the inode accordingly.
*/
void
xfs_trans_ichgtime(
struct xfs_trans *tp,
struct xfs_inode *ip,
int flags)
{
struct inode *inode = VFS_I(ip);
struct timespec64 tv;
ASSERT(tp);
ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
tv = current_time(inode);
if (flags & XFS_ICHGTIME_MOD)
inode->i_mtime = tv;
if (flags & XFS_ICHGTIME_CHG)
inode->i_ctime = tv;
if (flags & XFS_ICHGTIME_CREATE)
ip->i_d.di_crtime = tv;
}
/*
* This is called to mark the fields indicated in fieldmask as needing
* to be logged when the transaction is committed. The inode must
* already be associated with the given transaction.
*
* The values for fieldmask are defined in xfs_inode_item.h. We always
* log all of the core inode if any of it has changed, and we always log
* all of the inline data/extents/b-tree root if any of them has changed.
*/
void
xfs_trans_log_inode(
struct xfs_trans *tp,
struct xfs_inode *ip,
uint flags)
{
struct xfs_inode_log_item *iip = ip->i_itemp;
struct inode *inode = VFS_I(ip);
uint iversion_flags = 0;
ASSERT(iip);
ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
ASSERT(!xfs_iflags_test(ip, XFS_ISTALE));
tp->t_flags |= XFS_TRANS_DIRTY;
/*
* Don't bother with i_lock for the I_DIRTY_TIME check here, as races
* don't matter - we either will need an extra transaction in 24 hours
* to log the timestamps, or will clear already cleared fields in the
* worst case.
*/
if (inode->i_state & (I_DIRTY_TIME | I_DIRTY_TIME_EXPIRED)) {
spin_lock(&inode->i_lock);
inode->i_state &= ~(I_DIRTY_TIME | I_DIRTY_TIME_EXPIRED);
spin_unlock(&inode->i_lock);
}
/*
* First time we log the inode in a transaction, bump the inode change
* counter if it is configured for this to occur. While we have the
* inode locked exclusively for metadata modification, we can usually
* avoid setting XFS_ILOG_CORE if no one has queried the value since
* the last time it was incremented. If we have XFS_ILOG_CORE already
* set however, then go ahead and bump the i_version counter
* unconditionally.
*/
if (!test_and_set_bit(XFS_LI_DIRTY, &iip->ili_item.li_flags)) {
if (IS_I_VERSION(inode) &&
inode_maybe_inc_iversion(inode, flags & XFS_ILOG_CORE))
iversion_flags = XFS_ILOG_CORE;
}
/*
* Record the specific change for fdatasync optimisation. This allows
* fdatasync to skip log forces for inodes that are only timestamp
* dirty.
*/
spin_lock(&iip->ili_lock);
iip->ili_fsync_fields |= flags;
/*
* Always OR in the bits from the ili_last_fields field. This is to
* coordinate with the xfs_iflush() and xfs_iflush_done() routines in
* the eventual clearing of the ili_fields bits. See the big comment in
* xfs_iflush() for an explanation of this coordination mechanism.
*/
iip->ili_fields |= (flags | iip->ili_last_fields | iversion_flags);
spin_unlock(&iip->ili_lock);
}
int
xfs_trans_roll_inode(
struct xfs_trans **tpp,
struct xfs_inode *ip)
{
int error;
xfs_trans_log_inode(*tpp, ip, XFS_ILOG_CORE);
error = xfs_trans_roll(tpp);
if (!error)
xfs_trans_ijoin(*tpp, ip, 0);
return error;
}