From: yangerkun yangerkun@huawei.com

hulk inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I8JH5M?from=project-issue

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Parallel thread to add negative dentry under root dir. Sometimes later, 'systemctl daemon-reload' will report softlockup since __fsnotify_update_child_dentry_flags need update all child under root dentry without distinguish does it active or not. It will waste so long time with catching d_lock of root dentry. And other thread try to spin_lock d_lock will run overtime.

Limit negative dentry under dir can avoid this.

Signed-off-by: yangerkun yangerkun@huawei.com Signed-off-by: Zizhi Wo wozizhi@huawei.com --- fs/dcache.c | 43 ++++++++++++++++++++++++++++++++++++++++-- include/linux/dcache.h | 4 ++++ 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c index 7cdd8bbedd1c..c27aa8ff78f4 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -341,10 +341,18 @@ static inline void __d_set_inode_and_type(struct dentry *dentry, unsigned type_flags) { unsigned flags; + struct dentry *parent; + + parent = dentry->d_parent; + if ((dentry->d_flags & DCACHE_NEGATIVE_ACCOUNT) && parent) { + WARN_ON(!inode); + atomic_dec(&parent->d_neg_dnum); + }

dentry->d_inode = inode; flags = READ_ONCE(dentry->d_flags); - flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU); + flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU | + DCACHE_NEGATIVE_ACCOUNT); flags |= type_flags; smp_store_release(&dentry->d_flags, flags); } @@ -363,6 +371,7 @@ static inline void __d_clear_type_and_inode(struct dentry *dentry) static void dentry_free(struct dentry *dentry) { WARN_ON(!hlist_unhashed(&dentry->d_u.d_alias)); + WARN_ON(dentry->d_flags & DCACHE_NEGATIVE_ACCOUNT); if (unlikely(dname_external(dentry))) { struct external_name *p = external_name(dentry); if (likely(atomic_dec_and_test(&p->u.count))) { @@ -601,8 +610,14 @@ static void __dentry_kill(struct dentry *dentry) /* if it was on the hash then remove it */ __d_drop(dentry); dentry_unlist(dentry, parent); - if (parent) + if (parent) { + if (dentry->d_flags & DCACHE_NEGATIVE_ACCOUNT) { + atomic_dec(&parent->d_neg_dnum); + dentry->d_flags &= ~DCACHE_NEGATIVE_ACCOUNT; + } + spin_unlock(&parent->d_lock); + } if (dentry->d_inode) dentry_unlink_inode(dentry); else @@ -662,6 +677,8 @@ static inline struct dentry *lock_parent(struct dentry *dentry)

static inline bool retain_dentry(struct dentry *dentry) { + struct dentry *parent; + WARN_ON(d_in_lookup(dentry));

/* Unreachable? Get rid of it */ @@ -679,6 +696,27 @@ static inline bool retain_dentry(struct dentry *dentry) if (unlikely(dentry->d_flags & DCACHE_DONTCACHE)) return false;

+ if (unlikely(!dentry->d_parent)) + goto noparent; + + parent = dentry->d_parent; + /* Return false if it's negative */ + WARN_ON((atomic_read(&parent->d_neg_dnum) < 0)); + if (!dentry->d_inode) { + if (!(dentry->d_flags & DCACHE_NEGATIVE_ACCOUNT)) { + unsigned int flags = READ_ONCE(dentry->d_flags); + + flags |= DCACHE_NEGATIVE_ACCOUNT; + WRITE_ONCE(dentry->d_flags, flags); + atomic_inc(&parent->d_neg_dnum); + } + } + + if (!dentry->d_inode && + atomic_read(&parent->d_neg_dnum) >= NEG_DENTRY_LIMIT) + return false; + +noparent: /* retain; LRU fodder */ dentry->d_lockref.count--; if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST))) @@ -1809,6 +1847,7 @@ static struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name) seqcount_spinlock_init(&dentry->d_seq, &dentry->d_lock); dentry->d_inode = NULL; dentry->d_parent = dentry; + atomic_set(&dentry->d_neg_dnum, 0); dentry->d_sb = sb; dentry->d_op = NULL; dentry->d_fsdata = NULL; diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 6b351e009f59..1c5b08d804ce 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -77,6 +77,7 @@ extern const struct qstr dotdot_name; # endif #endif

+#define NEG_DENTRY_LIMIT 16384 #define d_lock d_lockref.lock

struct dentry { @@ -111,6 +112,8 @@ struct dentry { struct hlist_bl_node d_in_lookup_hash; /* only for in-lookup ones */ struct rcu_head d_rcu; } d_u; + /* negative dentry under this dentry, if it's dir */ + atomic_t d_neg_dnum; } __randomize_layout;

/* @@ -212,6 +215,7 @@ struct dentry_operations { #define DCACHE_PAR_LOOKUP 0x10000000 /* being looked up (with parent locked shared) */ #define DCACHE_DENTRY_CURSOR 0x20000000 #define DCACHE_NORCU 0x40000000 /* No RCU delay for freeing */ +#define DCACHE_NEGATIVE_ACCOUNT 0x80000000

extern seqlock_t rename_lock;