cgroup: don't skip seq_open on write only opens on pidlist files (ac1e69aa) · Commits · 戴 / test

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>

kernel/cgroup.c

+1 −12

Original line number	Diff line number	Diff line
		@@ -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,
		},
		{

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