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    Subject[PATCH 2/2] change close_files() to use rcu_lock_acquire() to shut up RCU-lockdep
    put_files_struct() and close_files() do rcu_read_lock() to make
    rcu_dereference_check_fdtable() happy.

    We can use rcu_lock_acquire(&rcu_lock_map) instead, this looks
    self-explanatory and this is nop without CONFIG_DEBUG_LOCK_ALLOC().

    While at it, change close_files() to return fdt, this avoids another
    rcu_read_lock() + files_fdtable() in put_files_struct().

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    ---
    fs/file.c | 20 +++++++++-----------
    1 files changed, 9 insertions(+), 11 deletions(-)

    diff --git a/fs/file.c b/fs/file.c
    index 957cbc0..716d747 100644
    --- a/fs/file.c
    +++ b/fs/file.c
    @@ -348,7 +348,7 @@ out:
    return NULL;
    }

    -static void close_files(struct files_struct * files)
    +static struct fdtable *close_files(struct files_struct * files)
    {
    int i, j;
    struct fdtable *fdt;
    @@ -358,11 +358,12 @@ static void close_files(struct files_struct * files)
    /*
    * It is safe to dereference the fd table without RCU or
    * ->file_lock because this is the last reference to the
    - * files structure. But use RCU to shut RCU-lockdep up.
    + * files structure. But we need to shut RCU-lockdep up.
    */
    - rcu_read_lock();
    + rcu_lock_acquire(&rcu_lock_map);
    fdt = files_fdtable(files);
    - rcu_read_unlock();
    + rcu_lock_release(&rcu_lock_map);
    +
    for (;;) {
    unsigned long set;
    i = j * BITS_PER_LONG;
    @@ -381,6 +382,8 @@ static void close_files(struct files_struct * files)
    set >>= 1;
    }
    }
    +
    + return fdt;
    }

    struct files_struct *get_files_struct(struct task_struct *task)
    @@ -398,14 +401,9 @@ struct files_struct *get_files_struct(struct task_struct *task)

    void put_files_struct(struct files_struct *files)
    {
    - struct fdtable *fdt;
    -
    if (atomic_dec_and_test(&files->count)) {
    - close_files(files);
    - /* not really needed, since nobody can see us */
    - rcu_read_lock();
    - fdt = files_fdtable(files);
    - rcu_read_unlock();
    + struct fdtable *fdt = close_files(files);
    +
    /* free the arrays if they are not embedded */
    if (fdt != &files->fdtab)
    __free_fdtable(fdt);
    --
    1.5.5.1


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