On 2018/06/16 4:40, Tetsuo Handa wrote:
> Hmm, there might be other locations calling percpu_rwsem_release() ?
There are other locations calling percpu_rwsem_release(), but quite few.
include/linux/fs.h:1494:#define __sb_writers_release(sb, lev) \
include/linux/fs.h-1495-
percpu_rwsem_release(&(sb)->s_writers.rw_sem[(lev)-1], 1, _THIS_IP_)
fs/btrfs/transaction.c:1821: __sb_writers_release(fs_info->sb,
SB_FREEZE_FS);
fs/aio.c:1566: __sb_writers_release(file_inode(file)->i_sb,
SB_FREEZE_WRITE);
fs/xfs/xfs_aops.c:211: __sb_writers_release(ioend->io_inode->i_sb,
SB_FREEZE_FS);
I'd like to check what atomic_long_read(&sem->rw_sem.count) says
when hung task is reported.
Dmitry, if you succeed to reproduce khungtaskd messages, can you try this patch?
---
include/linux/sched.h | 1 +
kernel/hung_task.c | 25 +++++++++++++++++++++++++
kernel/locking/percpu-rwsem.c | 2 ++
3 files changed, 28 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 87bf02d..af95251 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1179,6 +1179,7 @@ struct task_struct {
/* Used by LSM modules for access restriction: */
void *security;
#endif
+ struct percpu_rw_semaphore *pcpu_rwsem_read_waiting;
/*
* New fields for task_struct should be added above here, so that
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 32b4794..409cc82 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -18,6 +18,7 @@
#include <linux/utsname.h>
#include <linux/sched/signal.h>
#include <linux/sched/debug.h>
+#include <linux/percpu-rwsem.h>
#include <trace/events/sched.h>
@@ -77,6 +78,29 @@ static int __init hung_task_panic_setup(char *str)
.notifier_call = hung_task_panic,
};
+static void dump_percpu_rwsem_state(struct percpu_rw_semaphore *sem)
+{
+ unsigned int sum = 0;
+ int cpu;
+
+ if (!sem)
+ return;
+ pr_info("percpu_rw_semaphore(%p)\n", sem);
+ pr_info(" ->rw_sem.count=0x%lx\n",
+ atomic_long_read(&sem->rw_sem.count));
+ pr_info(" ->rss.gp_state=%d\n", sem->rss.gp_state);
+ pr_info(" ->rss.gp_count=%d\n", sem->rss.gp_count);
+ pr_info(" ->rss.cb_state=%d\n", sem->rss.cb_state);
+ pr_info(" ->rss.gp_type=%d\n", sem->rss.gp_type);
+ pr_info(" ->readers_block=%d\n", sem->readers_block);
+ for_each_possible_cpu(cpu)
+ sum += per_cpu(*sem->read_count, cpu);
+ pr_info(" ->read_count=%d\n", sum);
+ pr_info(" ->list_empty(rw_sem.wait_list)=%d\n",
+ list_empty(&sem->rw_sem.wait_list));
+ pr_info(" ->writer.task=%p\n", sem->writer.task);
+}
+
static void check_hung_task(struct task_struct *t, unsigned long timeout)
{
unsigned long switch_count = t->nvcsw + t->nivcsw;
@@ -122,6 +146,7 @@ static void check_hung_task(struct task_struct *t, unsigned
long timeout)
pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
" disables this message.\n");
sched_show_task(t);
+ dump_percpu_rwsem_state(t->pcpu_rwsem_read_waiting);
hung_task_show_lock = true;
}
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 883cf1b..b3654ab 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -82,7 +82,9 @@ int __percpu_down_read(struct percpu_rw_semaphore *sem, int
try)
/*
* Avoid lockdep for the down/up_read() we already have them.
*/
+ current->pcpu_rwsem_read_waiting = sem;
__down_read(&sem->rw_sem);
+ current->pcpu_rwsem_read_waiting = NULL;
this_cpu_inc(*sem->read_count);
__up_read(&sem->rw_sem);
--
1.8.3.1
