cgroup: don't guarantee cgroup.procs is sorted if sane_behavior (afb2bc14) · Commits · 戴 / test

include/linux/cgroup.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -275,6 +275,9 @@ enum {
		* - "tasks" is removed. Everything should be at process
		* granularity. Use "cgroup.procs" instead.
		*
		* - "cgroup.procs" is not sorted. pids will be unique unless they
		* got recycled inbetween reads.
		*
		* - "release_agent" and "notify_on_release" are removed.
		* Replacement notification mechanism will be implemented.
		*

kernel/cgroup.c

+46 −5

Original line number	Diff line number	Diff line
		@@ -3564,11 +3564,49 @@ after:
		return dest;
		}

		/*
		* The two pid files - task and cgroup.procs - guaranteed that the result
		* is sorted, which forced this whole pidlist fiasco. As pid order is
		* different per namespace, each namespace needs differently sorted list,
		* making it impossible to use, for example, single rbtree of member tasks
		* sorted by task pointer. As pidlists can be fairly large, allocating one
		* per open file is dangerous, so cgroup had to implement shared pool of
		* pidlists keyed by cgroup and namespace.
		*
		* All this extra complexity was caused by the original implementation
		* committing to an entirely unnecessary property. In the long term, we
		* want to do away with it. Explicitly scramble sort order if
		* sane_behavior so that no such expectation exists in the new interface.
		*
		* Scrambling is done by swapping every two consecutive bits, which is
		* non-identity one-to-one mapping which disturbs sort order sufficiently.
		*/
		static pid_t pid_fry(pid_t pid)
		{
		unsigned a = pid & 0x55555555;
		unsigned b = pid & 0xAAAAAAAA;

		return (a << 1) \| (b >> 1);
		}

		static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
		{
		if (cgroup_sane_behavior(cgrp))
		return pid_fry(pid);
		else
		return pid;
		}

		static int cmppid(const void a, const void b)
		{
		return (pid_t )a - (pid_t )b;
		}

		static int fried_cmppid(const void a, const void b)
		{
		return pid_fry((pid_t )a) - pid_fry((pid_t )b);
		}

		static struct cgroup_pidlist cgroup_pidlist_find(struct cgroup cgrp,
		enum cgroup_filetype type)
		{
		@@ -3656,6 +3694,9 @@ static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
		css_task_iter_end(&it);
		length = n;
		/* now sort & (if procs) strip out duplicates */
		if (cgroup_sane_behavior(cgrp))
		sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
		else
		sort(array, length, sizeof(pid_t), cmppid, NULL);
		if (type == CGROUP_FILE_PROCS)
		length = pidlist_uniq(array, length);
		@@ -3777,10 +3818,10 @@ static void cgroup_pidlist_start(struct seq_file s, loff_t *pos)

		while (index < end) {
		int mid = (index + end) / 2;
		if (l->list[mid] == pid) {
		if (cgroup_pid_fry(cgrp, l->list[mid]) == pid) {
		index = mid;
		break;
		} else if (l->list[mid] <= pid)
		} else if (cgroup_pid_fry(cgrp, l->list[mid]) <= pid)
		index = mid + 1;
		else
		end = mid;
		@@ -3791,7 +3832,7 @@ static void cgroup_pidlist_start(struct seq_file s, loff_t *pos)
		return NULL;
		/* Update the abstract position to be the actual pid that we found */
		iter = l->list + index;
		pos = iter;
		pos = cgroup_pid_fry(cgrp, iter);
		return iter;
		}

		@@ -3820,7 +3861,7 @@ static void cgroup_pidlist_next(struct seq_file s, void v, loff_t pos)
		if (p >= end) {
		return NULL;
		} else {
		pos = p;
		pos = cgroup_pid_fry(of->cgrp, p);
		return p;
		}
		}

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