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xfs: use WRITE_ONCE to update if_seq 

This adds ordering of the updates and makes sure we always see the if_seq
update before the extent tree is modified.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Christoph Hellwig 2018-08-07 10:57:12 -07:00 committed by Darrick J. Wong
parent a0e336ba3e
commit 2ba090d521
3 changed files with 21 additions and 6 deletions
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20
fs/xfs/libxfs/xfs_iext_tree.c
View File

@ -14,6 +14,7 @@
#include "xfs_inode_fork.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_bmap.h"
#include "xfs_trace.h"
/*
@ -612,6 +613,19 @@ xfs_iext_realloc_root(
cur->leaf = new;
}
/*
* Increment the sequence counter if we are on a COW fork. This allows
* the writeback code to skip looking for a COW extent if the COW fork
* hasn't changed. We use WRITE_ONCE here to ensure the update to the
* sequence counter is seen before the modifications to the extent
* tree itself take effect.
*/
static inline void xfs_iext_inc_seq(struct xfs_ifork *ifp, int state)
{
if (state & BMAP_COWFORK)
WRITE_ONCE(ifp->if_seq, READ_ONCE(ifp->if_seq) + 1);
}
void
xfs_iext_insert(
struct xfs_inode *ip,
@ -624,7 +638,7 @@ xfs_iext_insert(
struct xfs_iext_leaf *new = NULL;
int nr_entries, i;
ifp->if_seq++;
xfs_iext_inc_seq(ifp, state);
if (ifp->if_height == 0)
xfs_iext_alloc_root(ifp, cur);
@ -866,7 +880,7 @@ xfs_iext_remove(
ASSERT(ifp->if_u1.if_root != NULL);
ASSERT(xfs_iext_valid(ifp, cur));
ifp->if_seq++;
xfs_iext_inc_seq(ifp, state);
nr_entries = xfs_iext_leaf_nr_entries(ifp, leaf, cur->pos) - 1;
for (i = cur->pos; i < nr_entries; i++)
@ -974,7 +988,7 @@ xfs_iext_update_extent(
{
struct xfs_ifork *ifp = xfs_iext_state_to_fork(ip, state);
ifp->if_seq++;
xfs_iext_inc_seq(ifp, state);
if (cur->pos == 0) {
struct xfs_bmbt_irec old;

4
fs/xfs/xfs_aops.c
View File

@ -351,7 +351,7 @@ xfs_map_blocks(
if (imap_valid &&
(!xfs_inode_has_cow_data(ip) ||
wpc->io_type == XFS_IO_COW ||
wpc->cow_seq == ip->i_cowfp->if_seq))
wpc->cow_seq == READ_ONCE(ip->i_cowfp->if_seq)))
return 0;
if (XFS_FORCED_SHUTDOWN(mp))
@ -380,7 +380,7 @@ xfs_map_blocks(
xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, &imap))
cow_fsb = imap.br_startoff;
if (cow_fsb != NULLFILEOFF && cow_fsb <= offset_fsb) {
wpc->cow_seq = ip->i_cowfp->if_seq;
wpc->cow_seq = READ_ONCE(ip->i_cowfp->if_seq);
xfs_iunlock(ip, XFS_ILOCK_SHARED);
/*
* Truncate can race with writeback since writeback doesn't

3
fs/xfs/xfs_iomap.c
View File

@ -655,6 +655,7 @@ xfs_iomap_write_allocate(
unsigned int *cow_seq)
{
xfs_mount_t *mp = ip->i_mount;
struct xfs_ifork *ifp = XFS_IFORK_PTR(ip, whichfork);
xfs_fileoff_t offset_fsb, last_block;
xfs_fileoff_t end_fsb, map_start_fsb;
xfs_filblks_t count_fsb;
@ -768,7 +769,7 @@ xfs_iomap_write_allocate(
goto error0;
if (whichfork == XFS_COW_FORK)
*cow_seq = XFS_IFORK_PTR(ip, whichfork)->if_seq;
*cow_seq = READ_ONCE(ifp->if_seq);
xfs_iunlock(ip, XFS_ILOCK_EXCL);
}