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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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