103 lines
3.4 KiB
Diff
103 lines
3.4 KiB
Diff
From 0ae9b536ab4d44793251987a5c540feae252b40d Mon Sep 17 00:00:00 2001
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Message-Id: <0ae9b536ab4d44793251987a5c540feae252b40d.1601675152.git.zanussi@kernel.org>
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In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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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 172/333] fs/dcache: disable preemption on i_dir_seq's write
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side
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.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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include/linux/fs.h | 2 +-
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3 files changed, 9 insertions(+), 7 deletions(-)
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diff --git a/fs/dcache.c b/fs/dcache.c
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index 10225a9135fb..dcde8ffe384c 100644
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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(struct inode *dir)
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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 dentry *parent,
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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 dentry *parent,
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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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diff --git a/fs/inode.c b/fs/inode.c
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index c9eb5041ffae..e1fb0b743c96 100644
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--- a/fs/inode.c
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+++ b/fs/inode.c
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@@ -156,7 +156,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
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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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diff --git a/include/linux/fs.h b/include/linux/fs.h
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index 876bfb6df06a..0b102f962518 100644
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--- a/include/linux/fs.h
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+++ b/include/linux/fs.h
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@@ -679,7 +679,7 @@ 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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--
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2.17.1
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