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author | Waiman Long <longman@redhat.com> | 2021-04-15 22:54:26 +0300 |
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committer | Peter Zijlstra <peterz@infradead.org> | 2021-04-21 14:55:42 +0300 |
commit | ad789f84c9a145f8a18744c0387cec22ec51651e (patch) | |
tree | cc707b3f959392170239a2554edb5b2bab18a4ae /kernel/sched/debug.c | |
parent | 9d10a13d1e4c349b76f1c675a874a7f981d6d3b4 (diff) | |
download | linux-ad789f84c9a145f8a18744c0387cec22ec51651e.tar.xz |
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/sched/debug.c')
-rw-r--r-- | kernel/sched/debug.c | 42 |
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"); } |