diff options
Diffstat (limited to 'features/rt/fs-dcache-disable-preemption-on-i_dir_seq-s-write-si.patch')
| -rw-r--r-- | features/rt/fs-dcache-disable-preemption-on-i_dir_seq-s-write-si.patch | 98 |
1 files changed, 98 insertions, 0 deletions
diff --git a/features/rt/fs-dcache-disable-preemption-on-i_dir_seq-s-write-si.patch b/features/rt/fs-dcache-disable-preemption-on-i_dir_seq-s-write-si.patch new file mode 100644 index 00000000..0e3c58f2 --- /dev/null +++ b/features/rt/fs-dcache-disable-preemption-on-i_dir_seq-s-write-si.patch @@ -0,0 +1,98 @@ +From 3280c5c16fc06b062dce646186bf6d9449b03a5e Mon Sep 17 00:00:00 2001 +From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Date: Fri, 20 Oct 2017 11:29:53 +0200 +Subject: [PATCH 090/191] 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 <bigeasy@linutronix.de> +--- + fs/dcache.c | 12 +++++++----- + fs/inode.c | 2 +- + include/linux/fs.h | 2 +- + 3 files changed, 9 insertions(+), 7 deletions(-) + +diff --git a/fs/dcache.c b/fs/dcache.c +index 2c36711a222e..cd6405fd483a 100644 +--- a/fs/dcache.c ++++ b/fs/dcache.c +@@ -2537,9 +2537,10 @@ 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(); + } +@@ -2547,7 +2548,8 @@ 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) +@@ -2583,7 +2585,7 @@ 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)) { +@@ -2611,7 +2613,7 @@ 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 0672530acf7d..70a1230062e3 100644 +--- a/fs/inode.c ++++ b/fs/inode.c +@@ -158,7 +158,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode) + inode->i_pipe = 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/include/linux/fs.h b/include/linux/fs.h +index 4fa4b24535fd..9ac35f563f6e 100644 +--- a/include/linux/fs.h ++++ b/include/linux/fs.h +@@ -700,7 +700,7 @@ struct inode { + struct pipe_inode_info *i_pipe; + struct cdev *i_cdev; + char *i_link; +- unsigned i_dir_seq; ++ unsigned __i_dir_seq; + }; + + __u32 i_generation; +-- +2.19.1 + |