Date: Fri, 28 Oct 2016 23:05:11 +0200 From: Sebastian Andrzej Siewior To: Trond Myklebust Cc: Anna Schumaker , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de Subject: NFSv4: replace seqcount_t with a seqlock_t Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.18/older/patches-4.18.5-rt3.tar.xz The raw_write_seqcount_begin() in nfs4_reclaim_open_state() bugs me because it maps to preempt_disable() in -RT which I can't have at this point. So I took a look at the code. It the lockdep part was removed in commit abbec2da13f0 ("NFS: Use raw_write_seqcount_begin/end int nfs4_reclaim_open_state") because lockdep complained. The whole seqcount thing was introduced in commit c137afabe330 ("NFSv4: Allow the state manager to mark an open_owner as being recovered"). The recovery threads runs only once. write_seqlock() does not work on !RT because it disables preemption and it the writer side is preemptible (has to remain so despite the fact that it will block readers). Reported-by: kernel test robot Signed-off-by: Sebastian Andrzej Siewior --- fs/nfs/delegation.c | 4 ++-- fs/nfs/nfs4_fs.h | 2 +- fs/nfs/nfs4proc.c | 4 ++-- fs/nfs/nfs4state.c | 22 ++++++++++++++++------ 4 files changed, 21 insertions(+), 11 deletions(-) --- a/fs/nfs/delegation.c +++ b/fs/nfs/delegation.c @@ -152,11 +152,11 @@ static int nfs_delegation_claim_opens(st sp = state->owner; /* Block nfs4_proc_unlck */ mutex_lock(&sp->so_delegreturn_mutex); - seq = raw_seqcount_begin(&sp->so_reclaim_seqcount); + seq = read_seqbegin(&sp->so_reclaim_seqlock); err = nfs4_open_delegation_recall(ctx, state, stateid, type); if (!err) err = nfs_delegation_claim_locks(ctx, state, stateid); - if (!err && read_seqcount_retry(&sp->so_reclaim_seqcount, seq)) + if (!err && read_seqretry(&sp->so_reclaim_seqlock, seq)) err = -EAGAIN; mutex_unlock(&sp->so_delegreturn_mutex); put_nfs_open_context(ctx); --- a/fs/nfs/nfs4_fs.h +++ b/fs/nfs/nfs4_fs.h @@ -112,7 +112,7 @@ struct nfs4_state_owner { unsigned long so_flags; struct list_head so_states; struct nfs_seqid_counter so_seqid; - seqcount_t so_reclaim_seqcount; + seqlock_t so_reclaim_seqlock; struct mutex so_delegreturn_mutex; }; --- a/fs/nfs/nfs4proc.c +++ b/fs/nfs/nfs4proc.c @@ -2811,7 +2811,7 @@ static int _nfs4_open_and_get_state(stru unsigned int seq; int ret; - seq = raw_seqcount_begin(&sp->so_reclaim_seqcount); + seq = raw_seqcount_begin(&sp->so_reclaim_seqlock.seqcount); ret = _nfs4_proc_open(opendata, ctx); if (ret != 0) @@ -2849,7 +2849,7 @@ static int _nfs4_open_and_get_state(stru if (d_inode(dentry) == state->inode) { nfs_inode_attach_open_context(ctx); - if (read_seqcount_retry(&sp->so_reclaim_seqcount, seq)) + if (read_seqretry(&sp->so_reclaim_seqlock, seq)) nfs4_schedule_stateid_recovery(server, state); else pnfs_parse_lgopen(state->inode, opendata->lgp, ctx); --- a/fs/nfs/nfs4state.c +++ b/fs/nfs/nfs4state.c @@ -511,7 +511,7 @@ nfs4_alloc_state_owner(struct nfs_server nfs4_init_seqid_counter(&sp->so_seqid); atomic_set(&sp->so_count, 1); INIT_LIST_HEAD(&sp->so_lru); - seqcount_init(&sp->so_reclaim_seqcount); + seqlock_init(&sp->so_reclaim_seqlock); mutex_init(&sp->so_delegreturn_mutex); return sp; } @@ -1560,8 +1560,12 @@ static int nfs4_reclaim_open_state(struc * recovering after a network partition or a reboot from a * server that doesn't support a grace period. */ +#ifdef CONFIG_PREEMPT_RT_FULL + write_seqlock(&sp->so_reclaim_seqlock); +#else + write_seqcount_begin(&sp->so_reclaim_seqlock.seqcount); +#endif spin_lock(&sp->so_lock); - raw_write_seqcount_begin(&sp->so_reclaim_seqcount); restart: list_for_each_entry(state, &sp->so_states, open_states) { if (!test_and_clear_bit(ops->state_flag_bit, &state->flags)) @@ -1630,14 +1634,20 @@ static int nfs4_reclaim_open_state(struc spin_lock(&sp->so_lock); goto restart; } - raw_write_seqcount_end(&sp->so_reclaim_seqcount); spin_unlock(&sp->so_lock); +#ifdef CONFIG_PREEMPT_RT_FULL + write_sequnlock(&sp->so_reclaim_seqlock); +#else + write_seqcount_end(&sp->so_reclaim_seqlock.seqcount); +#endif return 0; out_err: nfs4_put_open_state(state); - spin_lock(&sp->so_lock); - raw_write_seqcount_end(&sp->so_reclaim_seqcount); - spin_unlock(&sp->so_lock); +#ifdef CONFIG_PREEMPT_RT_FULL + write_sequnlock(&sp->so_reclaim_seqlock); +#else + write_seqcount_end(&sp->so_reclaim_seqlock.seqcount); +#endif return status; }