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Message-ID: <53854368.6050306@gmail.com> Date: Wed, 28 May 2014 10:01:12 +0800 From: Niu Yawei <yawei.niu@...il.com> To: Christoph Hellwig <hch@...radead.org>, jack@...e.cz CC: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, yawei.niu@...el.com, andreas.dilger@...el.com, lai.siyao@...el.com Subject: Re: [PATCH 3/3 v2] quota: remove dqptr_sem The v2 patchset just removed dqptr_sem totally (not like v1 keeping it in quota_info), and I measured performance of both v1 & v2 patches, the improvements are same as the first big-one patch I sent. > Remove dqptr_sem to make quota code scalable: Remove the dqptr_sem, > accessing inode->i_dquot now protected by dquot_srcu, and changing > inode->i_dquot is now serialized by dq_data_lock. > > Signed-off-by: Lai Siyao <lai.siyao@...el.com> > Signed-off-by: Niu Yawei <yawei.niu@...el.com> > --- > fs/quota/dquot.c | 105 +++++++++++++++++++------------------------------ > fs/super.c | 1 - > include/linux/quota.h | 1 - > 3 files changed, 41 insertions(+), 66 deletions(-) > > diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c > index dc6f711..b86c88b 100644 > --- a/fs/quota/dquot.c > +++ b/fs/quota/dquot.c > @@ -96,13 +96,15 @@ > * Note that some things (eg. sb pointer, type, id) doesn't change during > * the life of the dquot structure and so needn't to be protected by a lock > * > - * Any operation working on dquots via inode pointers must hold dqptr_sem. If > - * operation is just reading pointers from inode (or not using them at all) the > - * read lock is enough. If pointers are altered function must hold write lock. > + * Operation accessing dquots via inode pointers are protected by dquot_srcu. > + * Operation of reading pointer needs srcu_read_lock(&dquot_srcu), and > + * synchronize_srcu(&dquot_srcu) is called before clear pointers to avoid > + * use after free. dq_data_lock is used to serialize the pointer setting and > + * clearing operations. > * Special care needs to be taken about S_NOQUOTA inode flag (marking that > * inode is a quota file). Functions adding pointers from inode to dquots have > - * to check this flag under dqptr_sem and then (if S_NOQUOTA is not set) they > - * have to do all pointer modifications before dropping dqptr_sem. This makes > + * to check this flag under dq_data_lock and then (if S_NOQUOTA is not set) they > + * have to do all pointer modifications before dropping dq_data_lock. This makes > * sure they cannot race with quotaon which first sets S_NOQUOTA flag and > * then drops all pointers to dquots from an inode. > * > @@ -116,21 +118,15 @@ > * spinlock to internal buffers before writing. > * > * Lock ordering (including related VFS locks) is the following: > - * dqonoff_mutex > i_mutex > journal_lock > dqptr_sem > dquot->dq_lock > > - * dqio_mutex > + * dqonoff_mutex > i_mutex > journal_lock > dquot->dq_lock > dqio_mutex > * dqonoff_mutex > i_mutex comes from dquot_quota_sync, dquot_enable, etc. > - * The lock ordering of dqptr_sem imposed by quota code is only dqonoff_sem > > - * dqptr_sem. But filesystem has to count with the fact that functions such as > - * dquot_alloc_space() acquire dqptr_sem and they usually have to be called > - * from inside a transaction to keep filesystem consistency after a crash. Also > - * filesystems usually want to do some IO on dquot from ->mark_dirty which is > - * called with dqptr_sem held. > */ > > static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dq_list_lock); > static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dq_state_lock); > __cacheline_aligned_in_smp DEFINE_SPINLOCK(dq_data_lock); > EXPORT_SYMBOL(dq_data_lock); > +DEFINE_STATIC_SRCU(dquot_srcu); > > void __quota_error(struct super_block *sb, const char *func, > const char *fmt, ...) > @@ -974,7 +970,6 @@ static inline int dqput_blocks(struct dquot *dquot) > /* > * Remove references to dquots from inode and add dquot to list for freeing > * if we have the last reference to dquot > - * We can't race with anybody because we hold dqptr_sem for writing... > */ > static int remove_inode_dquot_ref(struct inode *inode, int type, > struct list_head *tofree_head) > @@ -1035,13 +1030,15 @@ static void remove_dquot_ref(struct super_block *sb, int type, > * We have to scan also I_NEW inodes because they can already > * have quota pointer initialized. Luckily, we need to touch > * only quota pointers and these have separate locking > - * (dqptr_sem). > + * (dq_data_lock). > */ > + spin_lock(&dq_data_lock); > if (!IS_NOQUOTA(inode)) { > if (unlikely(inode_get_rsv_space(inode) > 0)) > reserved = 1; > remove_inode_dquot_ref(inode, type, tofree_head); > } > + spin_unlock(&dq_data_lock); > } > spin_unlock(&inode_sb_list_lock); > #ifdef CONFIG_QUOTA_DEBUG > @@ -1059,9 +1056,8 @@ static void drop_dquot_ref(struct super_block *sb, int type) > LIST_HEAD(tofree_head); > > if (sb->dq_op) { > - down_write(&sb_dqopt(sb)->dqptr_sem); > remove_dquot_ref(sb, type, &tofree_head); > - up_write(&sb_dqopt(sb)->dqptr_sem); > + synchronize_srcu(&dquot_srcu); > put_dquot_list(&tofree_head); > } > } > @@ -1392,9 +1388,6 @@ static int dquot_active(const struct inode *inode) > /* > * Initialize quota pointers in inode > * > - * We do things in a bit complicated way but by that we avoid calling > - * dqget() and thus filesystem callbacks under dqptr_sem. > - * > * It is better to call this function outside of any transaction as it > * might need a lot of space in journal for dquot structure allocation. > */ > @@ -1405,8 +1398,6 @@ static void __dquot_initialize(struct inode *inode, int type) > struct super_block *sb = inode->i_sb; > qsize_t rsv; > > - /* First test before acquiring mutex - solves deadlocks when we > - * re-enter the quota code and are already holding the mutex */ > if (!dquot_active(inode)) > return; > > @@ -1438,7 +1429,7 @@ static void __dquot_initialize(struct inode *inode, int type) > if (!dq_get) > return; > > - down_write(&sb_dqopt(sb)->dqptr_sem); > + spin_lock(&dq_data_lock); > if (IS_NOQUOTA(inode)) > goto out_err; > for (cnt = 0; cnt < MAXQUOTAS; cnt++) { > @@ -1458,15 +1449,12 @@ static void __dquot_initialize(struct inode *inode, int type) > * did a write before quota was turned on > */ > rsv = inode_get_rsv_space(inode); > - if (unlikely(rsv)) { > - spin_lock(&dq_data_lock); > + if (unlikely(rsv)) > dquot_resv_space(inode->i_dquot[cnt], rsv); > - spin_unlock(&dq_data_lock); > - } > } > } > out_err: > - up_write(&sb_dqopt(sb)->dqptr_sem); > + spin_unlock(&dq_data_lock); > /* Drop unused references */ > dqput_all(got); > } > @@ -1485,12 +1473,13 @@ static void __dquot_drop(struct inode *inode) > int cnt; > struct dquot *put[MAXQUOTAS]; > > - down_write(&sb_dqopt(inode->i_sb)->dqptr_sem); > + spin_lock(&dq_data_lock); > for (cnt = 0; cnt < MAXQUOTAS; cnt++) { > put[cnt] = inode->i_dquot[cnt]; > inode->i_dquot[cnt] = NULL; > } > - up_write(&sb_dqopt(inode->i_sb)->dqptr_sem); > + spin_unlock(&dq_data_lock); > + synchronize_srcu(&dquot_srcu); > dqput_all(put); > } > > @@ -1608,15 +1597,11 @@ static void inode_decr_space(struct inode *inode, qsize_t number, int reserve) > */ > int __dquot_alloc_space(struct inode *inode, qsize_t number, int flags) > { > - int cnt, ret = 0; > + int cnt, ret = 0, index; > struct dquot_warn warn[MAXQUOTAS]; > struct dquot **dquots = inode->i_dquot; > int reserve = flags & DQUOT_SPACE_RESERVE; > > - /* > - * First test before acquiring mutex - solves deadlocks when we > - * re-enter the quota code and are already holding the mutex > - */ > if (!dquot_active(inode)) { > inode_incr_space(inode, number, reserve); > goto out; > @@ -1625,7 +1610,7 @@ int __dquot_alloc_space(struct inode *inode, qsize_t number, int flags) > for (cnt = 0; cnt < MAXQUOTAS; cnt++) > warn[cnt].w_type = QUOTA_NL_NOWARN; > > - down_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + index = srcu_read_lock(&dquot_srcu); > spin_lock(&dq_data_lock); > for (cnt = 0; cnt < MAXQUOTAS; cnt++) { > if (!dquots[cnt]) > @@ -1652,7 +1637,7 @@ int __dquot_alloc_space(struct inode *inode, qsize_t number, int flags) > goto out_flush_warn; > mark_all_dquot_dirty(dquots); > out_flush_warn: > - up_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + srcu_read_unlock(&dquot_srcu, index); > flush_warnings(warn); > out: > return ret; > @@ -1664,17 +1649,16 @@ EXPORT_SYMBOL(__dquot_alloc_space); > */ > int dquot_alloc_inode(const struct inode *inode) > { > - int cnt, ret = 0; > + int cnt, ret = 0, index; > struct dquot_warn warn[MAXQUOTAS]; > struct dquot * const *dquots = inode->i_dquot; > > - /* First test before acquiring mutex - solves deadlocks when we > - * re-enter the quota code and are already holding the mutex */ > if (!dquot_active(inode)) > return 0; > for (cnt = 0; cnt < MAXQUOTAS; cnt++) > warn[cnt].w_type = QUOTA_NL_NOWARN; > - down_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + > + index = srcu_read_lock(&dquot_srcu); > spin_lock(&dq_data_lock); > for (cnt = 0; cnt < MAXQUOTAS; cnt++) { > if (!dquots[cnt]) > @@ -1694,7 +1678,7 @@ warn_put_all: > spin_unlock(&dq_data_lock); > if (ret == 0) > mark_all_dquot_dirty(dquots); > - up_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + srcu_read_unlock(&dquot_srcu, index); > flush_warnings(warn); > return ret; > } > @@ -1705,14 +1689,14 @@ EXPORT_SYMBOL(dquot_alloc_inode); > */ > int dquot_claim_space_nodirty(struct inode *inode, qsize_t number) > { > - int cnt; > + int cnt, index; > > if (!dquot_active(inode)) { > inode_claim_rsv_space(inode, number); > return 0; > } > > - down_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + index = srcu_read_lock(&dquot_srcu); > spin_lock(&dq_data_lock); > /* Claim reserved quotas to allocated quotas */ > for (cnt = 0; cnt < MAXQUOTAS; cnt++) { > @@ -1724,7 +1708,7 @@ int dquot_claim_space_nodirty(struct inode *inode, qsize_t number) > inode_claim_rsv_space(inode, number); > spin_unlock(&dq_data_lock); > mark_all_dquot_dirty(inode->i_dquot); > - up_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + srcu_read_unlock(&dquot_srcu, index); > return 0; > } > EXPORT_SYMBOL(dquot_claim_space_nodirty); > @@ -1734,14 +1718,14 @@ EXPORT_SYMBOL(dquot_claim_space_nodirty); > */ > void dquot_reclaim_space_nodirty(struct inode *inode, qsize_t number) > { > - int cnt; > + int cnt, index; > > if (!dquot_active(inode)) { > inode_reclaim_rsv_space(inode, number); > return; > } > > - down_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + index = srcu_read_lock(&dquot_srcu); > spin_lock(&dq_data_lock); > /* Claim reserved quotas to allocated quotas */ > for (cnt = 0; cnt < MAXQUOTAS; cnt++) { > @@ -1753,7 +1737,7 @@ void dquot_reclaim_space_nodirty(struct inode *inode, qsize_t number) > inode_reclaim_rsv_space(inode, number); > spin_unlock(&dq_data_lock); > mark_all_dquot_dirty(inode->i_dquot); > - up_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + srcu_read_unlock(&dquot_srcu, index); > return; > } > EXPORT_SYMBOL(dquot_reclaim_space_nodirty); > @@ -1766,16 +1750,14 @@ void __dquot_free_space(struct inode *inode, qsize_t number, int flags) > unsigned int cnt; > struct dquot_warn warn[MAXQUOTAS]; > struct dquot **dquots = inode->i_dquot; > - int reserve = flags & DQUOT_SPACE_RESERVE; > + int reserve = flags & DQUOT_SPACE_RESERVE, index; > > - /* First test before acquiring mutex - solves deadlocks when we > - * re-enter the quota code and are already holding the mutex */ > if (!dquot_active(inode)) { > inode_decr_space(inode, number, reserve); > return; > } > > - down_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + index = srcu_read_lock(&dquot_srcu); > spin_lock(&dq_data_lock); > for (cnt = 0; cnt < MAXQUOTAS; cnt++) { > int wtype; > @@ -1798,7 +1780,7 @@ void __dquot_free_space(struct inode *inode, qsize_t number, int flags) > goto out_unlock; > mark_all_dquot_dirty(dquots); > out_unlock: > - up_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + srcu_read_unlock(&dquot_srcu, index); > flush_warnings(warn); > } > EXPORT_SYMBOL(__dquot_free_space); > @@ -1811,13 +1793,12 @@ void dquot_free_inode(const struct inode *inode) > unsigned int cnt; > struct dquot_warn warn[MAXQUOTAS]; > struct dquot * const *dquots = inode->i_dquot; > + int index; > > - /* First test before acquiring mutex - solves deadlocks when we > - * re-enter the quota code and are already holding the mutex */ > if (!dquot_active(inode)) > return; > > - down_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + index = srcu_read_lock(&dquot_srcu); > spin_lock(&dq_data_lock); > for (cnt = 0; cnt < MAXQUOTAS; cnt++) { > int wtype; > @@ -1832,7 +1813,7 @@ void dquot_free_inode(const struct inode *inode) > } > spin_unlock(&dq_data_lock); > mark_all_dquot_dirty(dquots); > - up_read(&sb_dqopt(inode->i_sb)->dqptr_sem); > + srcu_read_unlock(&dquot_srcu, index); > flush_warnings(warn); > } > EXPORT_SYMBOL(dquot_free_inode); > @@ -1858,8 +1839,6 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to) > struct dquot_warn warn_from_inodes[MAXQUOTAS]; > struct dquot_warn warn_from_space[MAXQUOTAS]; > > - /* First test before acquiring mutex - solves deadlocks when we > - * re-enter the quota code and are already holding the mutex */ > if (IS_NOQUOTA(inode)) > return 0; > /* Initialize the arrays */ > @@ -1868,12 +1847,12 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to) > warn_from_inodes[cnt].w_type = QUOTA_NL_NOWARN; > warn_from_space[cnt].w_type = QUOTA_NL_NOWARN; > } > - down_write(&sb_dqopt(inode->i_sb)->dqptr_sem); > + > + spin_lock(&dq_data_lock); > if (IS_NOQUOTA(inode)) { /* File without quota accounting? */ > - up_write(&sb_dqopt(inode->i_sb)->dqptr_sem); > + spin_unlock(&dq_data_lock); > return 0; > } > - spin_lock(&dq_data_lock); > cur_space = inode_get_bytes(inode); > rsv_space = inode_get_rsv_space(inode); > space = cur_space + rsv_space; > @@ -1927,7 +1906,6 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to) > inode->i_dquot[cnt] = transfer_to[cnt]; > } > spin_unlock(&dq_data_lock); > - up_write(&sb_dqopt(inode->i_sb)->dqptr_sem); > > mark_all_dquot_dirty(transfer_from); > mark_all_dquot_dirty(transfer_to); > @@ -1941,7 +1919,6 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to) > return 0; > over_quota: > spin_unlock(&dq_data_lock); > - up_write(&sb_dqopt(inode->i_sb)->dqptr_sem); > flush_warnings(warn_to); > return ret; > } > diff --git a/fs/super.c b/fs/super.c > index 48377f7..a97aecf 100644 > --- a/fs/super.c > +++ b/fs/super.c > @@ -214,7 +214,6 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags) > lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key); > mutex_init(&s->s_dquot.dqio_mutex); > mutex_init(&s->s_dquot.dqonoff_mutex); > - init_rwsem(&s->s_dquot.dqptr_sem); > s->s_maxbytes = MAX_NON_LFS; > s->s_op = &default_op; > s->s_time_gran = 1000000000; > diff --git a/include/linux/quota.h b/include/linux/quota.h > index cc7494a..a1358ce 100644 > --- a/include/linux/quota.h > +++ b/include/linux/quota.h > @@ -389,7 +389,6 @@ struct quota_info { > unsigned int flags; /* Flags for diskquotas on this device */ > struct mutex dqio_mutex; /* lock device while I/O in progress */ > struct mutex dqonoff_mutex; /* Serialize quotaon & quotaoff */ > - struct rw_semaphore dqptr_sem; /* serialize ops using quota_info struct, pointers from inode to dquots */ > struct inode *files[MAXQUOTAS]; /* inodes of quotafiles */ > struct mem_dqinfo info[MAXQUOTAS]; /* Information for each quota type */ > const struct quota_format_ops *ops[MAXQUOTAS]; /* Operations for each type */ -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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