From 68c3b66eaa763a5cd8417107b415373341c8eb58 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Fri, 20 Oct 2017 11:29:53 +0200 Subject: [PATCH 328/352] fs/dcache: disable preemption on i_dir_seq's write side i_dir_seq is an opencoded seqcounter. Based on the code it looks like we could have two writers in parallel despite the fact that the d_lock is held. The problem is that during the write process on RT the preemption is still enabled and if this process is interrupted by a reader with RT priority then we lock up. To avoid that lock up I am disabling the preemption during the update. The rename of i_dir_seq is here to ensure to catch new write sides in future. Cc: stable-rt@vger.kernel.org Reported-by: Oleg.Karfich@wago.com Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Steven Rostedt (VMware) --- fs/dcache.c | 12 +++++++----- fs/inode.c | 2 +- fs/libfs.c | 6 ++++-- include/linux/fs.h | 2 +- 4 files changed, 13 insertions(+), 9 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 18581a9..1b81ea5 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2443,9 +2443,10 @@ EXPORT_SYMBOL(d_rehash); static inline unsigned start_dir_add(struct inode *dir) { + preempt_disable_rt(); for (;;) { - unsigned n = dir->i_dir_seq; - if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n) + unsigned n = dir->__i_dir_seq; + if (!(n & 1) && cmpxchg(&dir->__i_dir_seq, n, n + 1) == n) return n; cpu_relax(); } @@ -2453,7 +2454,8 @@ static inline unsigned start_dir_add(struct inode *dir) static inline void end_dir_add(struct inode *dir, unsigned n) { - smp_store_release(&dir->i_dir_seq, n + 2); + smp_store_release(&dir->__i_dir_seq, n + 2); + preempt_enable_rt(); } static void d_wait_lookup(struct dentry *dentry) @@ -2489,7 +2491,7 @@ struct dentry *d_alloc_parallel(struct dentry *parent, retry: rcu_read_lock(); - seq = smp_load_acquire(&parent->d_inode->i_dir_seq); + seq = smp_load_acquire(&parent->d_inode->__i_dir_seq); r_seq = read_seqbegin(&rename_lock); dentry = __d_lookup_rcu(parent, name, &d_seq); if (unlikely(dentry)) { @@ -2517,7 +2519,7 @@ struct dentry *d_alloc_parallel(struct dentry *parent, } hlist_bl_lock(b); - if (unlikely(READ_ONCE(parent->d_inode->i_dir_seq) != seq)) { + if (unlikely(READ_ONCE(parent->d_inode->__i_dir_seq) != seq)) { hlist_bl_unlock(b); rcu_read_unlock(); goto retry; diff --git a/fs/inode.c b/fs/inode.c index 1d1a957..99b9bae 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -153,7 +153,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode) inode->i_bdev = NULL; inode->i_cdev = NULL; inode->i_link = NULL; - inode->i_dir_seq = 0; + inode->__i_dir_seq = 0; inode->i_rdev = 0; inode->dirtied_when = 0; diff --git a/fs/libfs.c b/fs/libfs.c index 9588780a..9b37abd 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -89,7 +89,7 @@ static struct dentry *next_positive(struct dentry *parent, struct list_head *from, int count) { - unsigned *seq = &parent->d_inode->i_dir_seq, n; + unsigned *seq = &parent->d_inode->__i_dir_seq, n; struct dentry *res; struct list_head *p; bool skipped; @@ -122,8 +122,9 @@ static struct dentry *next_positive(struct dentry *parent, static void move_cursor(struct dentry *cursor, struct list_head *after) { struct dentry *parent = cursor->d_parent; - unsigned n, *seq = &parent->d_inode->i_dir_seq; + unsigned n, *seq = &parent->d_inode->__i_dir_seq; spin_lock(&parent->d_lock); + preempt_disable_rt(); for (;;) { n = *seq; if (!(n & 1) && cmpxchg(seq, n, n + 1) == n) @@ -136,6 +137,7 @@ static void move_cursor(struct dentry *cursor, struct list_head *after) else list_add_tail(&cursor->d_child, &parent->d_subdirs); smp_store_release(seq, n + 2); + preempt_enable_rt(); spin_unlock(&parent->d_lock); } diff --git a/include/linux/fs.h b/include/linux/fs.h index e22a270..7d8f1b8 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -708,7 +708,7 @@ struct inode { struct block_device *i_bdev; struct cdev *i_cdev; char *i_link; - unsigned i_dir_seq; + unsigned __i_dir_seq; }; __u32 i_generation; -- 2.7.4