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-rw-r--r--debian/patches-rt/0185-fs-dcache-disable-preemption-on-i_dir_seq-s-write-si.patch99
1 files changed, 99 insertions, 0 deletions
diff --git a/debian/patches-rt/0185-fs-dcache-disable-preemption-on-i_dir_seq-s-write-si.patch b/debian/patches-rt/0185-fs-dcache-disable-preemption-on-i_dir_seq-s-write-si.patch
new file mode 100644
index 000000000..e687b4d2d
--- /dev/null
+++ b/debian/patches-rt/0185-fs-dcache-disable-preemption-on-i_dir_seq-s-write-si.patch
@@ -0,0 +1,99 @@
+From 06c5210bfc8eff16e0d1df2430c7fcb07eae6c67 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 185/323] fs/dcache: disable preemption on i_dir_seq's write
+ side
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz
+
+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 1f4255ef8722..26a187abf13a 100644
+--- a/fs/dcache.c
++++ b/fs/dcache.c
+@@ -2503,9 +2503,10 @@ 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();
+ }
+@@ -2513,7 +2514,8 @@ 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)
+@@ -2549,7 +2551,7 @@ 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)) {
+@@ -2577,7 +2579,7 @@ 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 5c7139aa2bda..4ee8239c055f 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_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/include/linux/fs.h b/include/linux/fs.h
+index 82316863c71f..a29a0b8a1eca 100644
+--- a/include/linux/fs.h
++++ b/include/linux/fs.h
+@@ -699,7 +699,7 @@ 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;
+--
+2.43.0
+