[PATCHSET cgroup/for-3.16] cgroup: post unified hierarchy fixes and updates

[PATCHSET cgroup/for-3.16] cgroup: post unified hierarchy fixes and updates

[Tejun Heo]

Hello,

This patchset contains the following four patches.

 0001-cgroup-fix-offlining-child-waiting-in-cgroup_subtree.patch
 0002-cgroup-only-allow-space-as-the-separator-for-cgroup..patch
 0003-cgroup-use-restart_syscall-for-retries-after-offline.patch
 0004-cgroup-use-release_agent_path_lock-in-cgroup_release.patch

0001 fixes two bugs in cgroup_subtree_control_write().

0002 makes subtree_control parsing stricter.

0003 simplifies cgroup_substree_control_write() retry path by using
restart_syscall().

0004 makes cgroup_release_agent_show() use release_path_lock.  The
original conversion missed this one.

This patchset is on top of cgroup/for-3.16 12d3089c192c
("kernel/cpuset.c: convert printk to pr_foo()") and available on the
following git branch.

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-post-unified-updates

diffstat follows.

 kernel/cgroup.c |   33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

Thanks.

--
tejun

[PATCH 1/4] cgroup: fix offlining child waiting in cgroup_subtree_control_write()

[Tejun Heo]

cgroup_subtree_control_write() waits for offline to complete
child-by-child before enabling a controller; however, it has a couple
bugs.

* It doesn't initialize the wait_queue_t.  This can lead to infinite
  hang on the following schedule() among other things.

* It forgets to pin the child before releasing cgroup_tree_mutex and
  performing schedule().  The child may already be gone by the time it
  wakes up and invokes finish_wait().  Pin the child being waited on.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/cgroup.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 07815ef..54fd12d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2594,16 +2594,18 @@ retry:
 			 * cases, wait till it's gone using offline_waitq.
 			 */
 			cgroup_for_each_live_child(child, cgrp) {
-				wait_queue_t wait;
+				DEFINE_WAIT(wait);
 
 				if (!cgroup_css(child, ss))
 					continue;
 
+				cgroup_get(child);
 				prepare_to_wait(&child->offline_waitq, &wait,
 						TASK_UNINTERRUPTIBLE);
 				mutex_unlock(&cgroup_tree_mutex);
 				schedule();
 				finish_wait(&child->offline_waitq, &wait);
+				cgroup_put(child);
 				goto retry;
 			}
 
-- 
1.9.0

[PATCH 2/4] cgroup: only allow space as the separator for "cgroup.subtree_control"

[Tejun Heo]

I was confused that strsep() was equivalent to strtok_r() in skipping
over consecutive delimiters.  strsep() just splits at the first
occurrence of one of the delimiters which makes the parsing very
inflexible, which makes allowing multiple whitespace chars as
delimters kinda moot.  Let's just be consistently strict and require
list of tokens separated by a single space.  This is what
Documentation/cgroups/unified-hierarchy.txt describes too.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/cgroup.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 54fd12d..9066fe9 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2542,11 +2542,11 @@ static int cgroup_subtree_control_write(struct cgroup_subsys_state *dummy_css,
 	int ssid, ret;
 
 	/*
-	 * Parse input - white space separated list of subsystem names
-	 * prefixed with either + or -.
+	 * Parse input - space separated list of subsystem names prefixed
+	 * with either + or -.
 	 */
 	p = buffer;
-	while ((tok = strsep(&p, " \t\n"))) {
+	while ((tok = strsep(&p, " "))) {
 		for_each_subsys(ss, ssid) {
 			if (ss->disabled || strcmp(tok + 1, ss->name))
 				continue;
-- 
1.9.0

[PATCH v2 2/9] cgroup: update and fix parsing of "cgroup.subtree_control"

[Tejun Heo]

I was confused that strsep() was equivalent to strtok_r() in skipping
over consecutive delimiters.  strsep() just splits at the first
occurrence of one of the delimiters which makes the parsing very
inflexible, which makes allowing multiple whitespace chars as
delimters kinda moot.  Let's just be consistently strict and require
list of tokens separated by spaces.  This is what
Documentation/cgroups/unified-hierarchy.txt describes too.

Also, parsing may access beyond the end of the string if the string
ends with spaces or is zero-length.  Make sure it skips zero-length
tokens.  Note that this also ensures that the parser doesn't puke on
multiple consecutive spaces.

v2: Add zero-length token skipping.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/cgroup.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 54fd12d..9e6b4ac 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2542,11 +2542,13 @@ static int cgroup_subtree_control_write(struct cgroup_subsys_state *dummy_css,
 	int ssid, ret;
 
 	/*
-	 * Parse input - white space separated list of subsystem names
-	 * prefixed with either + or -.
+	 * Parse input - space separated list of subsystem names prefixed
+	 * with either + or -.
 	 */
 	p = buffer;
-	while ((tok = strsep(&p, " \t\n"))) {
+	while ((tok = strsep(&p, " "))) {
+		if (tok[0] =='\0')
+			continue;
 		for_each_subsys(ss, ssid) {
 			if (ss->disabled || strcmp(tok + 1, ss->name))
 				continue;
-- 
1.9.0

[PATCH 3/4] cgroup: use restart_syscall() for retries after offline waits in cgroup_subtree_control_write()

[Tejun Heo]

After waiting for a child to finish offline,
cgroup_subtree_control_write() jumps up to retry from after the input
parsing and active protection breaking.  This retry makes the
scheduled locking update more difficult.  Let's simplify it by
returning with restart_syscall() for retries.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/cgroup.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 9066fe9..3ced79a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2535,7 +2535,7 @@ out_finish:
 static int cgroup_subtree_control_write(struct cgroup_subsys_state *dummy_css,
 					struct cftype *cft, char *buffer)
 {
-	unsigned int enable_req = 0, disable_req = 0, enable, disable;
+	unsigned int enable = 0, disable = 0;
 	struct cgroup *cgrp = dummy_css->cgroup, *child;
 	struct cgroup_subsys *ss;
 	char *tok, *p;
@@ -2552,11 +2552,11 @@ static int cgroup_subtree_control_write(struct cgroup_subsys_state *dummy_css,
 				continue;
 
 			if (*tok == '+') {
-				enable_req |= 1 << ssid;
-				disable_req &= ~(1 << ssid);
+				enable |= 1 << ssid;
+				disable &= ~(1 << ssid);
 			} else if (*tok == '-') {
-				disable_req |= 1 << ssid;
-				enable_req &= ~(1 << ssid);
+				disable |= 1 << ssid;
+				enable &= ~(1 << ssid);
 			} else {
 				return -EINVAL;
 			}
@@ -2574,9 +2574,6 @@ static int cgroup_subtree_control_write(struct cgroup_subsys_state *dummy_css,
 	 */
 	cgroup_get(cgrp);
 	kernfs_break_active_protection(cgrp->control_kn);
-retry:
-	enable = enable_req;
-	disable = disable_req;
 
 	mutex_lock(&cgroup_tree_mutex);
 
@@ -2606,7 +2603,9 @@ retry:
 				schedule();
 				finish_wait(&child->offline_waitq, &wait);
 				cgroup_put(child);
-				goto retry;
+
+				ret = restart_syscall();
+				goto out_unbreak;
 			}
 
 			/* unavailable or not enabled on the parent? */
@@ -2690,6 +2689,7 @@ out_unlock:
 	mutex_unlock(&cgroup_mutex);
 out_unlock_tree:
 	mutex_unlock(&cgroup_tree_mutex);
+out_unbreak:
 	kernfs_unbreak_active_protection(cgrp->control_kn);
 	cgroup_put(cgrp);
 	return ret;
-- 
1.9.0

[PATCH 4/4] cgroup: use release_agent_path_lock in cgroup_release_agent_show()

[Tejun Heo]

release_path is now protected by release_agent_path_lock to allow
accessing it without grabbing cgroup_mutex; however,
cgroup_release_agent_show() was still grabbing cgroup_mutex.  Let's
convert it to release_agent_path_lock so that we don't have to worry
about this one for the planned locking updates.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/cgroup.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3ced79a..57c2021 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2373,11 +2373,10 @@ static int cgroup_release_agent_show(struct seq_file *seq, void *v)
 {
 	struct cgroup *cgrp = seq_css(seq)->cgroup;
 
-	if (!cgroup_lock_live_group(cgrp))
-		return -ENODEV;
+	spin_lock(&release_agent_path_lock);
 	seq_puts(seq, cgrp->root->release_agent_path);
+	spin_unlock(&release_agent_path_lock);
 	seq_putc(seq, '\n');
-	mutex_unlock(&cgroup_mutex);
 	return 0;
 }
 
-- 
1.9.0