cgroup: don't skip seq_open on write only opens on pidlist files

Currently, cgroup_pidlist_open() skips seq_open() and pidlist loading
if the file is opened write-only, which is a sensible optimization as
pidlist loading can be costly and there often are occasions where
tasks or cgroup.procs is opened write-only.  However, pidlist init and
release are planned to be moved to cgroup_pidlist_start/stop()
respectively which would make this optimization unnecessary.

This patch removes the optimization and always fully initializes
pidlist files regardless of open mode.  This will help moving pidlist
handling to start/stop by unifying rw paths and removes the need for
specifying cftype->release() in addition to .release in
cgroup_pidlist_operations as file->f_op is now always overridden.  As
pidlist files were the only user of cftype->release(), the next patch
will remove the method.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 34fd1be..1e09ded 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3781,12 +3781,7 @@ static void cgroup_release_pid_array(struct cgroup_pidlist *l)
 static int cgroup_pidlist_release(struct inode *inode, struct file *file)
 {
        struct cgroup_pidlist *l;
-       if (!(file->f_mode & FMODE_READ))
-               return 0;
-       /*
-        * the seq_file will only be initialized if the file was opened for
-        * reading; hence we check if it's not null only in that case.
-        */
+
        l = ((struct seq_file *)file->private_data)->private;
        cgroup_release_pid_array(l);
        return seq_release(inode, file);
@@ -3811,10 +3806,6 @@ static int cgroup_pidlist_open(struct file *file, enum cgroup_filetype type)
        struct cgroup_pidlist *l;
        int retval;
 
-       /* Nothing to do for write-only files */
-       if (!(file->f_mode & FMODE_READ))
-               return 0;
-
        /* have the array populated */
        retval = pidlist_array_load(cgrp, type, &l);
        if (retval)
@@ -3894,7 +3885,6 @@ static struct cftype cgroup_base_files[] = {
                .name = "cgroup.procs",
                .open = cgroup_procs_open,
                .write_u64 = cgroup_procs_write,
-               .release = cgroup_pidlist_release,
                .mode = S_IRUGO | S_IWUSR,
        },
        {
@@ -3919,7 +3909,6 @@ static struct cftype cgroup_base_files[] = {
                .flags = CFTYPE_INSANE,         /* use "procs" instead */
                .open = cgroup_tasks_open,
                .write_u64 = cgroup_tasks_write,
-               .release = cgroup_pidlist_release,
                .mode = S_IRUGO | S_IWUSR,
        },
        {