@@ -351,6 +351,19 @@ xfs_iget_recycle(
spin_unlock(&ip->i_flags_lock);
rcu_read_unlock();
+ /*
+ * VFS RCU pathwalk lookups dictate the same lifecycle rules for an
+ * inode recycle as for freeing an inode. I.e., we cannot reinit the
+ * inode structure until a grace period has elapsed from the last
+ * ->destroy_inode() call. In most cases a grace period has already
+ * elapsed if the inode was inactivated, but synchronize here as a
+ * last resort to guarantee correctness.
+ */
+ if (!poll_state_synchronize_rcu(ip->i_destroy_gp)) {
+ cond_synchronize_rcu(ip->i_destroy_gp);
+ trace_xfs_iget_recycle_stall(ip);
+ }
+
ASSERT(!rwsem_is_locked(&inode->i_rwsem));
error = xfs_reinit_inode(mp, inode);
if (error) {
@@ -1789,7 +1802,8 @@ xfs_check_delalloc(
/* Schedule the inode for reclaim. */
static void
xfs_inodegc_set_reclaimable(
- struct xfs_inode *ip)
+ struct xfs_inode *ip,
+ unsigned long destroy_gp)
{
struct xfs_mount *mp = ip->i_mount;
struct xfs_perag *pag;
@@ -1805,6 +1819,8 @@ xfs_inodegc_set_reclaimable(
spin_lock(&ip->i_flags_lock);
trace_xfs_inode_set_reclaimable(ip);
+ if (destroy_gp)
+ ip->i_destroy_gp = destroy_gp;
ip->i_flags &= ~(XFS_NEED_INACTIVE | XFS_INACTIVATING);
ip->i_flags |= XFS_IRECLAIMABLE;
xfs_perag_set_inode_tag(pag, XFS_INO_TO_AGINO(mp, ip->i_ino),
@@ -1826,7 +1842,8 @@ xfs_inodegc_inactivate(
{
trace_xfs_inode_inactivating(ip);
xfs_inactive(ip);
- xfs_inodegc_set_reclaimable(ip);
+ /* inactive inodes are assigned rcu state when first queued */
+ xfs_inodegc_set_reclaimable(ip, 0);
}
void
@@ -1997,7 +2014,8 @@ xfs_inodegc_want_flush_work(
*/
static void
xfs_inodegc_queue(
- struct xfs_inode *ip)
+ struct xfs_inode *ip,
+ unsigned long destroy_gp)
{
struct xfs_mount *mp = ip->i_mount;
struct xfs_inodegc *gc;
@@ -2007,6 +2025,7 @@ xfs_inodegc_queue(
trace_xfs_inode_set_need_inactive(ip);
spin_lock(&ip->i_flags_lock);
ip->i_flags |= XFS_NEED_INACTIVE;
+ ip->i_destroy_gp = destroy_gp;
spin_unlock(&ip->i_flags_lock);
gc = get_cpu_ptr(mp->m_inodegc);
@@ -2086,6 +2105,7 @@ xfs_inode_mark_reclaimable(
{
struct xfs_mount *mp = ip->i_mount;
bool need_inactive;
+ unsigned long destroy_gp;
XFS_STATS_INC(mp, vn_reclaim);
@@ -2094,15 +2114,22 @@ xfs_inode_mark_reclaimable(
*/
ASSERT_ALWAYS(!xfs_iflags_test(ip, XFS_ALL_IRECLAIM_FLAGS));
+ /*
+ * Poll the RCU subsystem as early as possible and pass the grace
+ * period cookie along to assign to the inode. This grace period must
+ * expire before the struct inode can be recycled.
+ */
+ destroy_gp = start_poll_synchronize_rcu();
+
need_inactive = xfs_inode_needs_inactive(ip);
if (need_inactive) {
- xfs_inodegc_queue(ip);
+ xfs_inodegc_queue(ip, destroy_gp);
return;
}
/* Going straight to reclaim, so drop the dquots. */
xfs_qm_dqdetach(ip);
- xfs_inodegc_set_reclaimable(ip);
+ xfs_inodegc_set_reclaimable(ip, destroy_gp);
}
/*
@@ -40,8 +40,9 @@ typedef struct xfs_inode {
/* Transaction and locking information. */
struct xfs_inode_log_item *i_itemp; /* logging information */
mrlock_t i_lock; /* inode lock */
- atomic_t i_pincount; /* inode pin count */
struct llist_node i_gclist; /* deferred inactivation list */
+ unsigned long i_destroy_gp; /* destroy rcugp cookie */
+ atomic_t i_pincount; /* inode pin count */
/*
* Bitsets of inode metadata that have been checked and/or are sick.
@@ -727,16 +727,19 @@ DECLARE_EVENT_CLASS(xfs_inode_class,
__field(dev_t, dev)
__field(xfs_ino_t, ino)
__field(unsigned long, iflags)
+ __field(unsigned long, destroy_gp)
),
TP_fast_assign(
__entry->dev = VFS_I(ip)->i_sb->s_dev;
__entry->ino = ip->i_ino;
__entry->iflags = ip->i_flags;
+ __entry->destroy_gp = ip->i_destroy_gp;
),
- TP_printk("dev %d:%d ino 0x%llx iflags 0x%lx",
+ TP_printk("dev %d:%d ino 0x%llx iflags 0x%lx destroy_gp 0x%lx",
MAJOR(__entry->dev), MINOR(__entry->dev),
__entry->ino,
- __entry->iflags)
+ __entry->iflags,
+ __entry->destroy_gp)
)
#define DEFINE_INODE_EVENT(name) \
@@ -746,6 +749,7 @@ DEFINE_EVENT(xfs_inode_class, name, \
DEFINE_INODE_EVENT(xfs_iget_skip);
DEFINE_INODE_EVENT(xfs_iget_recycle);
DEFINE_INODE_EVENT(xfs_iget_recycle_fail);
+DEFINE_INODE_EVENT(xfs_iget_recycle_stall);
DEFINE_INODE_EVENT(xfs_iget_hit);
DEFINE_INODE_EVENT(xfs_iget_miss);
The XFS inode allocation algorithm aggressively reuses recently freed inodes. This is historical behavior that has been in place for quite some time, since XFS was imported to mainline Linux. Once the VFS adopted RCUwalk path lookups (also some time ago), this behavior became slightly incompatible because the inode recycle path doesn't isolate concurrent access to the inode from the VFS. This has recently manifested as problems in the VFS when XFS happens to change the type or properties of a recently unlinked inode while still involved in an RCU lookup. For example, if the VFS refers to a previous incarnation of a symlink inode, obtains the ->get_link() callback from inode_operations, and the latter happens to change to a non-symlink type via a recycle event, the ->get_link() callback pointer is reset to NULL and the lookup results in a crash. To avoid this class of problem, isolate in-core inodes for recycling with an RCU grace period. This is the same level of protection the VFS expects for inactivated inodes that are never reused, and so guarantees no further concurrent access before the type or properties of the inode change. We don't want an unconditional synchronize_rcu() event here because that would result in a significant performance impact to mixed inode allocation workloads. Fortunately, we can take advantage of the recently added deferred inactivation mechanism to mitigate the need for an RCU wait in some cases. Deferred inactivation queues and batches the on-disk freeing of recently destroyed inodes, and so for non-sustained inactivation workloads increases the likelihood that a grace period has elapsed by the time an inode is freed and observable by the allocation code as a recycle candidate. We have to respect the lifecycle rules regardless of whether an inode was inactivated or not because of the fields modified by inode reinit. Therefore, capture the current RCU grace period cookie as early as possible at destroy time and use it at lookup time to conditionally sync an RCU grace period if one hadn't elapsed before the recycle attempt. Slightly adjust struct xfs_inode to fit the new field into padding holes that conveniently preexist in the same cacheline as the deferred inactivation list. Note that this patch alone introduces a significant negative impact to mixed file allocation and removal workloads because the allocation algorithm aggressively attempts to reuse recently freed inodes. This results in frequent RCU grace period synchronization stalls in the allocation path. This problem is mitigated by forthcoming patches to track and avoid recycling of inodes with pending RCU grace periods. Signed-off-by: Brian Foster <bfoster@redhat.com> --- fs/xfs/xfs_icache.c | 37 ++++++++++++++++++++++++++++++++----- fs/xfs/xfs_inode.h | 3 ++- fs/xfs/xfs_trace.h | 8 ++++++-- 3 files changed, 40 insertions(+), 8 deletions(-)