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cgroup: pids: use atomic64_t for pids->limit

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Because pids->limit can be changed concurrently (but we don't want to
take a lock because it would be needlessly expensive), use atomic64_ts
instead.

Fixes: commit 49b786ea14 ("cgroup: implement the PIDs subsystem")
Cc: stable@vger.kernel.org # v4.3+
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Aleksa Sarai 2019-10-17 02:50:01 +11:00 committed by Tejun Heo
parent 1a99fcc035
commit a713af394c
1 changed files with 6 additions and 5 deletions
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11
kernel/cgroup/pids.c
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@ -45,7 +45,7 @@ struct pids_cgroup {
* %PIDS_MAX = (%PID_MAX_LIMIT + 1).
*/
atomic64_t counter;
int64_t limit;
atomic64_t limit;
/* Handle for "pids.events" */
struct cgroup_file events_file;
@ -73,8 +73,8 @@ pids_css_alloc(struct cgroup_subsys_state *parent)
if (!pids)
return ERR_PTR(-ENOMEM);
pids->limit = PIDS_MAX;
atomic64_set(&pids->counter, 0);
atomic64_set(&pids->limit, PIDS_MAX);
atomic64_set(&pids->events_limit, 0);
return &pids->css;
}
@ -146,13 +146,14 @@ static int pids_try_charge(struct pids_cgroup *pids, int num)
for (p = pids; parent_pids(p); p = parent_pids(p)) {
int64_t new = atomic64_add_return(num, &p->counter);
int64_t limit = atomic64_read(&p->limit);
/*
* Since new is capped to the maximum number of pid_t, if
* p->limit is %PIDS_MAX then we know that this test will never
* fail.
*/
if (new > p->limit)
if (new > limit)
goto revert;
}
@ -277,7 +278,7 @@ static ssize_t pids_max_write(struct kernfs_open_file *of, char *buf,
* Limit updates don't need to be mutex'd, since it isn't
* critical that any racing fork()s follow the new limit.
*/
pids->limit = limit;
atomic64_set(&pids->limit, limit);
return nbytes;
}
@ -285,7 +286,7 @@ static int pids_max_show(struct seq_file *sf, void *v)
{
struct cgroup_subsys_state *css = seq_css(sf);
struct pids_cgroup *pids = css_pids(css);
int64_t limit = pids->limit;
int64_t limit = atomic64_read(&pids->limit);
if (limit >= PIDS_MAX)
seq_printf(sf, "%s\n", PIDS_MAX_STR);