From 0c5e80bd579f7bec3704bad6c1f72b13b0d73b53 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Mon, 10 Nov 2025 14:22:57 +0100 Subject: [PATCH] xfs: use a lockref for the xfs_dquot reference count The xfs_dquot structure currently uses the anti-pattern of using the in-object lock that protects the content to also serialize reference count updates for the structure, leading to a cumbersome free path. This is partially papered over by the fact that we never free the dquot directly but always through the LRU. Switch to use a lockref instead and move the reference counter manipulations out of q_qlock. To make this work, xfs_qm_flush_one and xfs_qm_flush_one are converted to acquire a dquot reference while flushing to integrate with the lockref "get if not dead" scheme. Signed-off-by: Christoph Hellwig Reviewed-by: Darrick J. Wong Signed-off-by: Carlos Maiolino --- fs/xfs/libxfs/xfs_quota_defs.h | 4 +-- fs/xfs/xfs_dquot.c | 17 ++++++------ fs/xfs/xfs_dquot.h | 6 ++-- fs/xfs/xfs_qm.c | 50 ++++++++++++++++------------------ fs/xfs/xfs_trace.h | 2 +- 5 files changed, 37 insertions(+), 42 deletions(-) diff --git a/fs/xfs/libxfs/xfs_quota_defs.h b/fs/xfs/libxfs/xfs_quota_defs.h index 763d941a8420c..551d7ae46c5c2 100644 --- a/fs/xfs/libxfs/xfs_quota_defs.h +++ b/fs/xfs/libxfs/xfs_quota_defs.h @@ -29,11 +29,9 @@ typedef uint8_t xfs_dqtype_t; * flags for q_flags field in the dquot. */ #define XFS_DQFLAG_DIRTY (1u << 0) /* dquot is dirty */ -#define XFS_DQFLAG_FREEING (1u << 1) /* dquot is being torn down */ #define XFS_DQFLAG_STRINGS \ - { XFS_DQFLAG_DIRTY, "DIRTY" }, \ - { XFS_DQFLAG_FREEING, "FREEING" } + { XFS_DQFLAG_DIRTY, "DIRTY" } /* * We have the possibility of all three quota types being active at once, and diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c index c2326cee7fae8..34c325524ab9d 100644 --- a/fs/xfs/xfs_dquot.c +++ b/fs/xfs/xfs_dquot.c @@ -816,20 +816,17 @@ restart: return NULL; } - mutex_lock(&dqp->q_qlock); - if (dqp->q_flags & XFS_DQFLAG_FREEING) { - mutex_unlock(&dqp->q_qlock); + if (!lockref_get_not_dead(&dqp->q_lockref)) { mutex_unlock(&qi->qi_tree_lock); trace_xfs_dqget_freeing(dqp); delay(1); goto restart; } - - dqp->q_nrefs++; mutex_unlock(&qi->qi_tree_lock); trace_xfs_dqget_hit(dqp); XFS_STATS_INC(mp, xs_qm_dqcachehits); + mutex_lock(&dqp->q_qlock); return dqp; } @@ -866,7 +863,7 @@ xfs_qm_dqget_cache_insert( /* Return a locked dquot to the caller, with a reference taken. */ mutex_lock(&dqp->q_qlock); - dqp->q_nrefs = 1; + lockref_init(&dqp->q_lockref); qi->qi_dquots++; out_unlock: @@ -1124,18 +1121,22 @@ void xfs_qm_dqput( struct xfs_dquot *dqp) { - ASSERT(dqp->q_nrefs > 0); ASSERT(XFS_DQ_IS_LOCKED(dqp)); trace_xfs_dqput(dqp); - if (--dqp->q_nrefs == 0) { + if (lockref_put_or_lock(&dqp->q_lockref)) + goto out_unlock; + + if (!--dqp->q_lockref.count) { struct xfs_quotainfo *qi = dqp->q_mount->m_quotainfo; trace_xfs_dqput_free(dqp); if (list_lru_add_obj(&qi->qi_lru, &dqp->q_lru)) XFS_STATS_INC(dqp->q_mount, xs_qm_dquot_unused); } + spin_unlock(&dqp->q_lockref.lock); +out_unlock: mutex_unlock(&dqp->q_qlock); } diff --git a/fs/xfs/xfs_dquot.h b/fs/xfs/xfs_dquot.h index 10c39b8cdd039..c56fbc39d0890 100644 --- a/fs/xfs/xfs_dquot.h +++ b/fs/xfs/xfs_dquot.h @@ -71,7 +71,7 @@ struct xfs_dquot { xfs_dqtype_t q_type; uint16_t q_flags; xfs_dqid_t q_id; - uint q_nrefs; + struct lockref q_lockref; int q_bufoffset; xfs_daddr_t q_blkno; xfs_fileoff_t q_fileoffset; @@ -231,9 +231,7 @@ void xfs_dquot_detach_buf(struct xfs_dquot *dqp); static inline struct xfs_dquot *xfs_qm_dqhold(struct xfs_dquot *dqp) { - mutex_lock(&dqp->q_qlock); - dqp->q_nrefs++; - mutex_unlock(&dqp->q_qlock); + lockref_get(&dqp->q_lockref); return dqp; } diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c index 3e88bea9a4657..f98f9fdac0b5d 100644 --- a/fs/xfs/xfs_qm.c +++ b/fs/xfs/xfs_qm.c @@ -126,14 +126,16 @@ xfs_qm_dqpurge( void *data) { struct xfs_quotainfo *qi = dqp->q_mount->m_quotainfo; - int error = -EAGAIN; - mutex_lock(&dqp->q_qlock); - if ((dqp->q_flags & XFS_DQFLAG_FREEING) || dqp->q_nrefs != 0) - goto out_unlock; - - dqp->q_flags |= XFS_DQFLAG_FREEING; + spin_lock(&dqp->q_lockref.lock); + if (dqp->q_lockref.count > 0 || __lockref_is_dead(&dqp->q_lockref)) { + spin_unlock(&dqp->q_lockref.lock); + return -EAGAIN; + } + lockref_mark_dead(&dqp->q_lockref); + spin_unlock(&dqp->q_lockref.lock); + mutex_lock(&dqp->q_qlock); xfs_qm_dqunpin_wait(dqp); xfs_dqflock(dqp); @@ -144,6 +146,7 @@ xfs_qm_dqpurge( */ if (XFS_DQ_IS_DIRTY(dqp)) { struct xfs_buf *bp = NULL; + int error; /* * We don't care about getting disk errors here. We need @@ -151,9 +154,9 @@ xfs_qm_dqpurge( */ error = xfs_dquot_use_attached_buf(dqp, &bp); if (error == -EAGAIN) { - xfs_dqfunlock(dqp); - dqp->q_flags &= ~XFS_DQFLAG_FREEING; - goto out_unlock; + /* resurrect the refcount from the dead. */ + dqp->q_lockref.count = 0; + goto out_funlock; } if (!bp) goto out_funlock; @@ -192,10 +195,6 @@ out_funlock: xfs_qm_dqdestroy(dqp); return 0; - -out_unlock: - mutex_unlock(&dqp->q_qlock); - return error; } /* @@ -468,7 +467,7 @@ xfs_qm_dquot_isolate( struct xfs_qm_isolate *isol = arg; enum lru_status ret = LRU_SKIP; - if (!mutex_trylock(&dqp->q_qlock)) + if (!spin_trylock(&dqp->q_lockref.lock)) goto out_miss_busy; /* @@ -476,7 +475,7 @@ xfs_qm_dquot_isolate( * from the LRU, leave it for the freeing task to complete the freeing * process rather than risk it being free from under us here. */ - if (dqp->q_flags & XFS_DQFLAG_FREEING) + if (__lockref_is_dead(&dqp->q_lockref)) goto out_miss_unlock; /* @@ -485,16 +484,15 @@ xfs_qm_dquot_isolate( * again. */ ret = LRU_ROTATE; - if (XFS_DQ_IS_DIRTY(dqp) || atomic_read(&dqp->q_pincount) > 0) { + if (XFS_DQ_IS_DIRTY(dqp) || atomic_read(&dqp->q_pincount) > 0) goto out_miss_unlock; - } /* * This dquot has acquired a reference in the meantime remove it from * the freelist and try again. */ - if (dqp->q_nrefs) { - mutex_unlock(&dqp->q_qlock); + if (dqp->q_lockref.count) { + spin_unlock(&dqp->q_lockref.lock); XFS_STATS_INC(dqp->q_mount, xs_qm_dqwants); trace_xfs_dqreclaim_want(dqp); @@ -518,10 +516,9 @@ xfs_qm_dquot_isolate( /* * Prevent lookups now that we are past the point of no return. */ - dqp->q_flags |= XFS_DQFLAG_FREEING; - mutex_unlock(&dqp->q_qlock); + lockref_mark_dead(&dqp->q_lockref); + spin_unlock(&dqp->q_lockref.lock); - ASSERT(dqp->q_nrefs == 0); list_lru_isolate_move(lru, &dqp->q_lru, &isol->dispose); XFS_STATS_DEC(dqp->q_mount, xs_qm_dquot_unused); trace_xfs_dqreclaim_done(dqp); @@ -529,7 +526,7 @@ xfs_qm_dquot_isolate( return LRU_REMOVED; out_miss_unlock: - mutex_unlock(&dqp->q_qlock); + spin_unlock(&dqp->q_lockref.lock); out_miss_busy: trace_xfs_dqreclaim_busy(dqp); XFS_STATS_INC(dqp->q_mount, xs_qm_dqreclaim_misses); @@ -1467,9 +1464,10 @@ xfs_qm_flush_one( struct xfs_buf *bp = NULL; int error = 0; + if (!lockref_get_not_dead(&dqp->q_lockref)) + return 0; + mutex_lock(&dqp->q_qlock); - if (dqp->q_flags & XFS_DQFLAG_FREEING) - goto out_unlock; if (!XFS_DQ_IS_DIRTY(dqp)) goto out_unlock; @@ -1489,7 +1487,7 @@ xfs_qm_flush_one( xfs_buf_delwri_queue(bp, buffer_list); xfs_buf_relse(bp); out_unlock: - mutex_unlock(&dqp->q_qlock); + xfs_qm_dqput(dqp); return error; } diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h index 79b8641880ab9..46d21eb11ccbf 100644 --- a/fs/xfs/xfs_trace.h +++ b/fs/xfs/xfs_trace.h @@ -1350,7 +1350,7 @@ DECLARE_EVENT_CLASS(xfs_dquot_class, __entry->id = dqp->q_id; __entry->type = dqp->q_type; __entry->flags = dqp->q_flags; - __entry->nrefs = dqp->q_nrefs; + __entry->nrefs = data_race(dqp->q_lockref.count); __entry->res_bcount = dqp->q_blk.reserved; __entry->res_rtbcount = dqp->q_rtb.reserved; -- 2.47.3