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Subject[PATCH 5/7] module: take rcu_read_lock_sched() for /proc read
Date
In the seq file operations, it still hold module_mutex for just reading
the module list, switch to rcu_read_lock_sched() too.

A new function seq_list_start_rcu() is introduced for this.

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>

---
fs/seq_file.c | 12 ++++++++++++
include/linux/seq_file.h | 2 ++
kernel/module.c | 6 +++---
3 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 4023d6b..5b01e04 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -674,6 +674,18 @@ struct list_head *seq_list_start(struct list_head *head, loff_t pos)
}
EXPORT_SYMBOL(seq_list_start);

+struct list_head *seq_list_start_rcu(struct list_head *head, loff_t pos)
+{
+ struct list_head *lh = head;
+
+ list_for_each_continue_rcu(lh, head)
+ if (pos-- == 0)
+ return lh;
+
+ return NULL;
+}
+EXPORT_SYMBOL(seq_list_start_rcu);
+
struct list_head *seq_list_start_head(struct list_head *head, loff_t pos)
{
if (!pos)
diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index 44f1514..7848189 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -130,6 +130,8 @@ int seq_release_private(struct inode *, struct file *);

extern struct list_head *seq_list_start(struct list_head *head,
loff_t pos);
+extern struct list_head *seq_list_start_rcu(struct list_head *head,
+ loff_t pos);
extern struct list_head *seq_list_start_head(struct list_head *head,
loff_t pos);
extern struct list_head *seq_list_next(void *v, struct list_head *head,
diff --git a/kernel/module.c b/kernel/module.c
index 73e1f95..06e7dc5 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3313,8 +3313,8 @@ static char *module_flags(struct module *mod, char *buf)
/* Called by the /proc file system to return a list of modules. */
static void *m_start(struct seq_file *m, loff_t *pos)
{
- mutex_lock(&module_mutex);
- return seq_list_start(&modules, *pos);
+ rcu_read_lock_sched();
+ return seq_list_start_rcu(&modules, *pos);
}

static void *m_next(struct seq_file *m, void *p, loff_t *pos)
@@ -3324,7 +3324,7 @@ static void *m_next(struct seq_file *m, void *p, loff_t *pos)

static void m_stop(struct seq_file *m, void *p)
{
- mutex_unlock(&module_mutex);
+ rcu_read_unlock_sched();
}

static int m_show(struct seq_file *m, void *p)
--
1.7.7.6


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