Added "#ifndef CONFIG_RWSEM_GENERIC_SPINLOCK" check. >From 88f979f8f019f32de94327878ef1f7ccb7500321 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> Date: Tue, 10 Jul 2018 20:43:18 +0900 Subject: [PATCH v2] locking/lockdep: Dump state of percpu_rwsem upon hung up.
This is a temporary patch which should not go to linux.git. syzbot is hitting hung task problems at __sb_start_write() [1]. While hung tasks at __sb_start_write() suggest that filesystem was frozen, syzbot is not doing ioctl(FIFREEZE) requests. Therefore, the root cause of hung tasks is currently unknown. As a first step for debugging this problem, let's check what atomic_long_read(&sem->rw_sem.count) says when hung task is reported. Since it is impossible to reproduce this problem locally, this patch was made in order to test linux-next.git using syzbot infrastructure. [1] https://syzkaller.appspot.com/bug?id=287aa8708bc940d0ca1645223c53dd4c2d203be6 Signed-off-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Ingo Molnar <mi...@redhat.com> Cc: Will Deacon <will.dea...@arm.com> Cc: Dmitry Vyukov <dvyu...@google.com> --- include/linux/sched.h | 1 + kernel/hung_task.c | 27 +++++++++++++++++++++++++++ kernel/locking/percpu-rwsem.c | 2 ++ 3 files changed, 30 insertions(+) diff --git a/include/linux/sched.h b/include/linux/sched.h index 2974378..df56c65 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1191,6 +1191,7 @@ struct task_struct { /* Used by LSM modules for access restriction: */ void *security; #endif + struct percpu_rw_semaphore *pcpu_rwsem_read_waiting; #ifdef CONFIG_GCC_PLUGIN_STACKLEAK unsigned long lowest_stack; diff --git a/kernel/hung_task.c b/kernel/hung_task.c index b9132d1..43975df 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> @@ -82,6 +83,31 @@ 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) +{ +#ifndef CONFIG_RWSEM_GENERIC_SPINLOCK + 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); +#endif +} + static void check_hung_task(struct task_struct *t, unsigned long timeout) { unsigned long switch_count = t->nvcsw + t->nivcsw; @@ -130,6 +156,7 @@ 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
