120 lines
3.7 KiB
Diff
120 lines
3.7 KiB
Diff
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Fri, 20 Oct 2017 11:29:53 +0200
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Subject: [PATCH] fs/dcache: disable preemption on i_dir_seq's write side
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.1-rt3.tar.xz
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i_dir_seq is an opencoded seqcounter. Based on the code it looks like we
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could have two writers in parallel despite the fact that the d_lock is
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held. The problem is that during the write process on RT the preemption
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is still enabled and if this process is interrupted by a reader with RT
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priority then we lock up.
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To avoid that lock up I am disabling the preemption during the update.
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The rename of i_dir_seq is here to ensure to catch new write sides in
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future.
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Cc: stable-rt@vger.kernel.org
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Reported-by: Oleg.Karfich@wago.com
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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fs/dcache.c | 12 +++++++-----
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fs/inode.c | 2 +-
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fs/libfs.c | 6 ++++--
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include/linux/fs.h | 2 +-
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4 files changed, 13 insertions(+), 9 deletions(-)
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--- a/fs/dcache.c
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+++ b/fs/dcache.c
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@@ -2404,9 +2404,10 @@ EXPORT_SYMBOL(d_rehash);
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static inline unsigned start_dir_add(struct inode *dir)
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{
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+ preempt_disable_rt();
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for (;;) {
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- unsigned n = dir->i_dir_seq;
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- if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n)
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+ unsigned n = dir->__i_dir_seq;
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+ if (!(n & 1) && cmpxchg(&dir->__i_dir_seq, n, n + 1) == n)
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return n;
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cpu_relax();
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}
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@@ -2414,7 +2415,8 @@ static inline unsigned start_dir_add(str
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static inline void end_dir_add(struct inode *dir, unsigned n)
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{
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- smp_store_release(&dir->i_dir_seq, n + 2);
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+ smp_store_release(&dir->__i_dir_seq, n + 2);
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+ preempt_enable_rt();
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}
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static void d_wait_lookup(struct dentry *dentry)
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@@ -2447,7 +2449,7 @@ struct dentry *d_alloc_parallel(struct d
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retry:
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rcu_read_lock();
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- seq = smp_load_acquire(&parent->d_inode->i_dir_seq);
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+ seq = smp_load_acquire(&parent->d_inode->__i_dir_seq);
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r_seq = read_seqbegin(&rename_lock);
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dentry = __d_lookup_rcu(parent, name, &d_seq);
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if (unlikely(dentry)) {
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@@ -2475,7 +2477,7 @@ struct dentry *d_alloc_parallel(struct d
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}
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hlist_bl_lock(b);
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- if (unlikely(READ_ONCE(parent->d_inode->i_dir_seq) != seq)) {
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+ if (unlikely(READ_ONCE(parent->d_inode->__i_dir_seq) != seq)) {
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hlist_bl_unlock(b);
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rcu_read_unlock();
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goto retry;
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--- a/fs/inode.c
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+++ b/fs/inode.c
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@@ -155,7 +155,7 @@ int inode_init_always(struct super_block
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inode->i_bdev = NULL;
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inode->i_cdev = NULL;
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inode->i_link = NULL;
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- inode->i_dir_seq = 0;
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+ inode->__i_dir_seq = 0;
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inode->i_rdev = 0;
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inode->dirtied_when = 0;
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--- a/fs/libfs.c
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+++ b/fs/libfs.c
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@@ -90,7 +90,7 @@ static struct dentry *next_positive(stru
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struct list_head *from,
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int count)
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{
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- unsigned *seq = &parent->d_inode->i_dir_seq, n;
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+ unsigned *seq = &parent->d_inode->__i_dir_seq, n;
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struct dentry *res;
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struct list_head *p;
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bool skipped;
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@@ -123,8 +123,9 @@ static struct dentry *next_positive(stru
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static void move_cursor(struct dentry *cursor, struct list_head *after)
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{
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struct dentry *parent = cursor->d_parent;
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- unsigned n, *seq = &parent->d_inode->i_dir_seq;
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+ unsigned n, *seq = &parent->d_inode->__i_dir_seq;
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spin_lock(&parent->d_lock);
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+ preempt_disable_rt();
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for (;;) {
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n = *seq;
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if (!(n & 1) && cmpxchg(seq, n, n + 1) == n)
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@@ -137,6 +138,7 @@ static void move_cursor(struct dentry *c
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else
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list_add_tail(&cursor->d_child, &parent->d_subdirs);
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smp_store_release(seq, n + 2);
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+ preempt_enable_rt();
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spin_unlock(&parent->d_lock);
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}
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--- a/include/linux/fs.h
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+++ b/include/linux/fs.h
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@@ -669,7 +669,7 @@ struct inode {
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struct block_device *i_bdev;
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struct cdev *i_cdev;
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char *i_link;
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- unsigned i_dir_seq;
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+ unsigned __i_dir_seq;
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};
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__u32 i_generation;
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