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authorWaiman Long <longman@redhat.com>2021-04-15 15:54:26 -0400
committerPeter Zijlstra <peterz@infradead.org>2021-04-21 13:55:42 +0200
commitad789f84c9a145f8a18744c0387cec22ec51651e (patch)
treecc707b3f959392170239a2554edb5b2bab18a4ae /kernel
parent9d10a13d1e4c349b76f1c675a874a7f981d6d3b4 (diff)
sched/debug: Fix cgroup_path[] serialization
The handling of sysrq key can be activated by echoing the key to /proc/sysrq-trigger or via the magic key sequence typed into a terminal that is connected to the system in some way (serial, USB or other mean). In the former case, the handling is done in a user context. In the latter case, it is likely to be in an interrupt context. Currently in print_cpu() of kernel/sched/debug.c, sched_debug_lock is taken with interrupt disabled for the whole duration of the calls to print_*_stats() and print_rq() which could last for the quite some time if the information dump happens on the serial console. If the system has many cpus and the sched_debug_lock is somehow busy (e.g. parallel sysrq-t), the system may hit a hard lockup panic depending on the actually serial console implementation of the system. The purpose of sched_debug_lock is to serialize the use of the global cgroup_path[] buffer in print_cpu(). The rests of the printk calls don't need serialization from sched_debug_lock. Calling printk() with interrupt disabled can still be problematic if multiple instances are running. Allocating a stack buffer of PATH_MAX bytes is not feasible because of the limited size of the kernel stack. The solution implemented in this patch is to allow only one caller at a time to use the full size group_path[], while other simultaneous callers will have to use shorter stack buffers with the possibility of path name truncation. A "..." suffix will be printed if truncation may have happened. The cgroup path name is provided for informational purpose only, so occasional path name truncation should not be a big problem. Fixes: efe25c2c7b3a ("sched: Reinstate group names in /proc/sched_debug") Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20210415195426.6677-1-longman@redhat.com
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/debug.c42
1 files changed, 29 insertions, 13 deletions
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 7251fc477a11..9c882f20803e 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -8,8 +8,6 @@
*/
#include "sched.h"
-static DEFINE_SPINLOCK(sched_debug_lock);
-
/*
* This allows printing both to /proc/sched_debug and
* to the console
@@ -476,16 +474,37 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group
#endif
#ifdef CONFIG_CGROUP_SCHED
+static DEFINE_SPINLOCK(sched_debug_lock);
static char group_path[PATH_MAX];
-static char *task_group_path(struct task_group *tg)
+static void task_group_path(struct task_group *tg, char *path, int plen)
{
- if (autogroup_path(tg, group_path, PATH_MAX))
- return group_path;
+ if (autogroup_path(tg, path, plen))
+ return;
- cgroup_path(tg->css.cgroup, group_path, PATH_MAX);
+ cgroup_path(tg->css.cgroup, path, plen);
+}
- return group_path;
+/*
+ * Only 1 SEQ_printf_task_group_path() caller can use the full length
+ * group_path[] for cgroup path. Other simultaneous callers will have
+ * to use a shorter stack buffer. A "..." suffix is appended at the end
+ * of the stack buffer so that it will show up in case the output length
+ * matches the given buffer size to indicate possible path name truncation.
+ */
+#define SEQ_printf_task_group_path(m, tg, fmt...) \
+{ \
+ if (spin_trylock(&sched_debug_lock)) { \
+ task_group_path(tg, group_path, sizeof(group_path)); \
+ SEQ_printf(m, fmt, group_path); \
+ spin_unlock(&sched_debug_lock); \
+ } else { \
+ char buf[128]; \
+ char *bufend = buf + sizeof(buf) - 3; \
+ task_group_path(tg, buf, bufend - buf); \
+ strcpy(bufend - 1, "..."); \
+ SEQ_printf(m, fmt, buf); \
+ } \
}
#endif
@@ -512,7 +531,7 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
SEQ_printf(m, " %d %d", task_node(p), task_numa_group_id(p));
#endif
#ifdef CONFIG_CGROUP_SCHED
- SEQ_printf(m, " %s", task_group_path(task_group(p)));
+ SEQ_printf_task_group_path(m, task_group(p), " %s")
#endif
SEQ_printf(m, "\n");
@@ -549,7 +568,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
#ifdef CONFIG_FAIR_GROUP_SCHED
SEQ_printf(m, "\n");
- SEQ_printf(m, "cfs_rq[%d]:%s\n", cpu, task_group_path(cfs_rq->tg));
+ SEQ_printf_task_group_path(m, cfs_rq->tg, "cfs_rq[%d]:%s\n", cpu);
#else
SEQ_printf(m, "\n");
SEQ_printf(m, "cfs_rq[%d]:\n", cpu);
@@ -620,7 +639,7 @@ void print_rt_rq(struct seq_file *m, int cpu, struct rt_rq *rt_rq)
{
#ifdef CONFIG_RT_GROUP_SCHED
SEQ_printf(m, "\n");
- SEQ_printf(m, "rt_rq[%d]:%s\n", cpu, task_group_path(rt_rq->tg));
+ SEQ_printf_task_group_path(m, rt_rq->tg, "rt_rq[%d]:%s\n", cpu);
#else
SEQ_printf(m, "\n");
SEQ_printf(m, "rt_rq[%d]:\n", cpu);
@@ -672,7 +691,6 @@ void print_dl_rq(struct seq_file *m, int cpu, struct dl_rq *dl_rq)
static void print_cpu(struct seq_file *m, int cpu)
{
struct rq *rq = cpu_rq(cpu);
- unsigned long flags;
#ifdef CONFIG_X86
{
@@ -723,13 +741,11 @@ do { \
}
#undef P
- spin_lock_irqsave(&sched_debug_lock, flags);
print_cfs_stats(m, cpu);
print_rt_stats(m, cpu);
print_dl_stats(m, cpu);
print_rq(m, rq, cpu);
- spin_unlock_irqrestore(&sched_debug_lock, flags);
SEQ_printf(m, "\n");
}