[PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up.

[PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up.

[Tetsuo Handa]

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-kernel@I-love.SAKURA.ne.jp>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
---
 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 cf1edc0..2aaaf49 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1183,6 +1183,7 @@ 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..03d7d9b 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 +83,29 @@ 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;
@@ -130,6 +154,7 @@ 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

Re: [PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up.

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 6382 bytes --]

Hi Tetsuo,

I love your patch! Yet something to improve:

[auto build test ERROR on next-20180706]
[also build test ERROR on v4.18-rc3]
[cannot apply to tip/auto-latest tip/sched/core linus/master v4.18-rc3 v4.18-rc2 v4.18-rc1]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Tetsuo-Handa/locking-lockdep-Dump-state-of-percpu_rwsem-upon-hung-up/20180707-143406
config: mips-allmodconfig (attached as .config)
compiler: mips-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.2.0 make.cross ARCH=mips 

All error/warnings (new ones prefixed by >>):

   In file included from include/linux/kernel.h:14:0,
                    from include/asm-generic/bug.h:18,
                    from arch/mips/include/asm/bug.h:42,
                    from include/linux/bug.h:5,
                    from include/linux/mmdebug.h:5,
                    from include/linux/mm.h:9,
                    from kernel/hung_task.c:8:
   kernel/hung_task.c: In function 'dump_percpu_rwsem_state':
>> kernel/hung_task.c:95:20: error: passing argument 1 of 'atomic_long_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
      atomic_long_read(&sem->rw_sem.count));
                       ^
   include/linux/printk.h:311:34: note: in definition of macro 'pr_info'
     printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
                                     ^~~~~~~~~~~
   In file included from include/linux/atomic.h:1309:0,
                    from arch/mips/include/asm/processor.h:14,
                    from arch/mips/include/asm/thread_info.h:16,
                    from include/linux/thread_info.h:38,
                    from include/asm-generic/preempt.h:5,
                    from ./arch/mips/include/generated/asm/preempt.h:1,
                    from include/linux/preempt.h:81,
                    from include/linux/spinlock.h:51,
                    from include/linux/mmzone.h:8,
                    from include/linux/gfp.h:6,
                    from include/linux/mm.h:10,
                    from kernel/hung_task.c:8:
   include/asm-generic/atomic-long.h:41:20: note: expected 'const atomic_long_t * {aka const struct <anonymous> *}' but argument is of type '__s32 * {aka int *}'
    static inline long atomic_long_read##mo(const atomic_long_t *l)  \
                       ^
>> include/asm-generic/atomic-long.h:47:1: note: in expansion of macro 'ATOMIC_LONG_READ_OP'
    ATOMIC_LONG_READ_OP()
    ^~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/atomic_long_read +95 kernel/hung_task.c

   > 8	#include <linux/mm.h>
     9	#include <linux/cpu.h>
    10	#include <linux/nmi.h>
    11	#include <linux/init.h>
    12	#include <linux/delay.h>
    13	#include <linux/freezer.h>
    14	#include <linux/kthread.h>
    15	#include <linux/lockdep.h>
    16	#include <linux/export.h>
    17	#include <linux/sysctl.h>
    18	#include <linux/utsname.h>
    19	#include <linux/sched/signal.h>
    20	#include <linux/sched/debug.h>
    21	#include <linux/percpu-rwsem.h>
    22	
    23	#include <trace/events/sched.h>
    24	
    25	/*
    26	 * The number of tasks checked:
    27	 */
    28	int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
    29	
    30	/*
    31	 * Limit number of tasks checked in a batch.
    32	 *
    33	 * This value controls the preemptibility of khungtaskd since preemption
    34	 * is disabled during the critical section. It also controls the size of
    35	 * the RCU grace period. So it needs to be upper-bound.
    36	 */
    37	#define HUNG_TASK_BATCHING 1024
    38	
    39	/*
    40	 * Zero means infinite timeout - no checking done:
    41	 */
    42	unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
    43	
    44	/*
    45	 * Zero (default value) means use sysctl_hung_task_timeout_secs:
    46	 */
    47	unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
    48	
    49	int __read_mostly sysctl_hung_task_warnings = 10;
    50	
    51	static int __read_mostly did_panic;
    52	static bool hung_task_show_lock;
    53	static bool hung_task_call_panic;
    54	
    55	static struct task_struct *watchdog_task;
    56	
    57	/*
    58	 * Should we panic (and reboot, if panic_timeout= is set) when a
    59	 * hung task is detected:
    60	 */
    61	unsigned int __read_mostly sysctl_hung_task_panic =
    62					CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
    63	
    64	static int __init hung_task_panic_setup(char *str)
    65	{
    66		int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
    67	
    68		if (rc)
    69			return rc;
    70		return 1;
    71	}
    72	__setup("hung_task_panic=", hung_task_panic_setup);
    73	
    74	static int
    75	hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
    76	{
    77		did_panic = 1;
    78	
    79		return NOTIFY_DONE;
    80	}
    81	
    82	static struct notifier_block panic_block = {
    83		.notifier_call = hung_task_panic,
    84	};
    85	
    86	static void dump_percpu_rwsem_state(struct percpu_rw_semaphore *sem)
    87	{
    88		unsigned int sum = 0;
    89		int cpu;
    90	
    91		if (!sem)
    92			return;
    93		pr_info("percpu_rw_semaphore(%p)\n", sem);
    94		pr_info("  ->rw_sem.count=0x%lx\n",
  > 95			atomic_long_read(&sem->rw_sem.count));
    96		pr_info("  ->rss.gp_state=%d\n", sem->rss.gp_state);
    97		pr_info("  ->rss.gp_count=%d\n", sem->rss.gp_count);
    98		pr_info("  ->rss.cb_state=%d\n", sem->rss.cb_state);
    99		pr_info("  ->rss.gp_type=%d\n", sem->rss.gp_type);
   100		pr_info("  ->readers_block=%d\n", sem->readers_block);
   101		for_each_possible_cpu(cpu)
   102			sum += per_cpu(*sem->read_count, cpu);
   103		pr_info("  ->read_count=%d\n", sum);
   104		pr_info("  ->list_empty(rw_sem.wait_list)=%d\n",
   105		       list_empty(&sem->rw_sem.wait_list));
   106		pr_info("  ->writer.task=%p\n", sem->writer.task);
   107	}
   108	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 56614 bytes --]

Re: [PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up.

[Tetsuo Handa]

Hello.

Thanks for doing build test, but I don't understand what is wrong.
As far as I can see, "struct percpu_rw_semaphore" contains "struct rw_semaphore"
and "struct rw_semaphore" contains "atomic_long_t count".
Then, why trying to read using atomic_long_read(&sem->rw_sem.count) causes

  note: expected 'const atomic_long_t * {aka const struct <anonymous> *}' but argument is of type '__s32 * {aka int *}'

warning? Is mips using different type?

struct percpu_rw_semaphore {
        struct rcu_sync         rss;
        unsigned int __percpu   *read_count;
        struct rw_semaphore     rw_sem; /* slowpath */
        struct rcuwait          writer; /* blocked writer */
        int                     readers_block;
};

/* All arch specific implementations share the same struct */
struct rw_semaphore {
        atomic_long_t count;
        struct list_head wait_list;
        raw_spinlock_t wait_lock;
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
        struct optimistic_spin_queue osq; /* spinner MCS lock */
        /*
         * Write owner. Used as a speculative check to see
         * if the owner is running on the cpu.
         */
        struct task_struct *owner;
#endif
#ifdef CONFIG_DEBUG_LOCK_ALLOC
        struct lockdep_map      dep_map;
#endif
};

On 2018/07/07 20:31, kbuild test robot wrote:
> Hi Tetsuo,
> 
> I love your patch! Yet something to improve:
> 
> [auto build test ERROR on next-20180706]
> [also build test ERROR on v4.18-rc3]
> [cannot apply to tip/auto-latest tip/sched/core linus/master v4.18-rc3 v4.18-rc2 v4.18-rc1]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> 
> url:    https://github.com/0day-ci/linux/commits/Tetsuo-Handa/locking-lockdep-Dump-state-of-percpu_rwsem-upon-hung-up/20180707-143406
> config: mips-allmodconfig (attached as .config)
> compiler: mips-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         GCC_VERSION=7.2.0 make.cross ARCH=mips 
> 
> All error/warnings (new ones prefixed by >>):
> 
>    In file included from include/linux/kernel.h:14:0,
>                     from include/asm-generic/bug.h:18,
>                     from arch/mips/include/asm/bug.h:42,
>                     from include/linux/bug.h:5,
>                     from include/linux/mmdebug.h:5,
>                     from include/linux/mm.h:9,
>                     from kernel/hung_task.c:8:
>    kernel/hung_task.c: In function 'dump_percpu_rwsem_state':
>>> kernel/hung_task.c:95:20: error: passing argument 1 of 'atomic_long_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
>       atomic_long_read(&sem->rw_sem.count));
>                        ^
>    include/linux/printk.h:311:34: note: in definition of macro 'pr_info'
>      printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
>                                      ^~~~~~~~~~~
>    In file included from include/linux/atomic.h:1309:0,
>                     from arch/mips/include/asm/processor.h:14,
>                     from arch/mips/include/asm/thread_info.h:16,
>                     from include/linux/thread_info.h:38,
>                     from include/asm-generic/preempt.h:5,
>                     from ./arch/mips/include/generated/asm/preempt.h:1,
>                     from include/linux/preempt.h:81,
>                     from include/linux/spinlock.h:51,
>                     from include/linux/mmzone.h:8,
>                     from include/linux/gfp.h:6,
>                     from include/linux/mm.h:10,
>                     from kernel/hung_task.c:8:
>    include/asm-generic/atomic-long.h:41:20: note: expected 'const atomic_long_t * {aka const struct <anonymous> *}' but argument is of type '__s32 * {aka int *}'
>     static inline long atomic_long_read##mo(const atomic_long_t *l)  \
>                        ^
>>> include/asm-generic/atomic-long.h:47:1: note: in expansion of macro 'ATOMIC_LONG_READ_OP'
>     ATOMIC_LONG_READ_OP()
>     ^~~~~~~~~~~~~~~~~~~
>    cc1: some warnings being treated as errors

Re: [PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up.

[Tetsuo Handa]

From 2642b4a1904259384f2018ea8df03ac49509c57a Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SKAURA.ne.jp>
Date: Tue, 10 Jul 2018 15:01:20 +0900
Subject: [PATCH] locking/rwsem: Convert the other sem->count to 'atomic_long_t'

Since "locking/rwsem: Convert sem->count to 'atomic_long_t'" forgot to
convert "struct rw_semaphore"->count in linux/rwsem-spinlock.h which is
used when CONFIG_RWSEM_GENERIC_SPINLOCK=y, trying to access it in MIPS
architecture causes build error due to type mismatch.

  error: passing argument 1 of 'atomic_long_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
  note: expected 'const atomic_long_t * {aka const struct <anonymous> *}' but argument is of type '__s32 * {aka int *}'

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SKAURA.ne.jp>
Reported-by: kbuild test robot <lkp@intel.com>
Fixes: 8ee62b1870be8e63 ("locking/rwsem: Convert sem->count to 'atomic_long_t'")
Cc: stable <stable@vger.kernel.org> # v4.8+
Cc: Jason Low <jason.low2@hpe.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 include/linux/rwsem-spinlock.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rwsem-spinlock.h b/include/linux/rwsem-spinlock.h
index e475683..1164965 100644
--- a/include/linux/rwsem-spinlock.h
+++ b/include/linux/rwsem-spinlock.h
@@ -22,7 +22,7 @@
  * - if wait_list is not empty, then there are processes waiting for the semaphore
  */
 struct rw_semaphore {
-	__s32			count;
+	atomic_long_t		count;
 	raw_spinlock_t		wait_lock;
 	struct list_head	wait_list;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-- 
2.7.4

Re: [PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up.

[Will Deacon]

On Tue, Jul 10, 2018 at 03:10:51PM +0900, Tetsuo Handa wrote:
> From 2642b4a1904259384f2018ea8df03ac49509c57a Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SKAURA.ne.jp>
> Date: Tue, 10 Jul 2018 15:01:20 +0900
> Subject: [PATCH] locking/rwsem: Convert the other sem->count to 'atomic_long_t'
> 
> Since "locking/rwsem: Convert sem->count to 'atomic_long_t'" forgot to
> convert "struct rw_semaphore"->count in linux/rwsem-spinlock.h which is
> used when CONFIG_RWSEM_GENERIC_SPINLOCK=y, trying to access it in MIPS
> architecture causes build error due to type mismatch.
> 
>   error: passing argument 1 of 'atomic_long_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
>   note: expected 'const atomic_long_t * {aka const struct <anonymous> *}' but argument is of type '__s32 * {aka int *}'
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SKAURA.ne.jp>
> Reported-by: kbuild test robot <lkp@intel.com>
> Fixes: 8ee62b1870be8e63 ("locking/rwsem: Convert sem->count to 'atomic_long_t'")
> Cc: stable <stable@vger.kernel.org> # v4.8+
> Cc: Jason Low <jason.low2@hpe.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> ---
>  include/linux/rwsem-spinlock.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Hmm, how come you don't have to update kernel/locking/rwsem-spinlock.c
as well? I see stuff such as:

	sem->count += woken;

in there.

Will

Re: [PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up.

[Peter Zijlstra]

On Tue, Jul 10, 2018 at 03:10:51PM +0900, Tetsuo Handa wrote:
> From 2642b4a1904259384f2018ea8df03ac49509c57a Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SKAURA.ne.jp>
> Date: Tue, 10 Jul 2018 15:01:20 +0900
> Subject: [PATCH] locking/rwsem: Convert the other sem->count to 'atomic_long_t'
> 
> Since "locking/rwsem: Convert sem->count to 'atomic_long_t'" forgot to
> convert "struct rw_semaphore"->count in linux/rwsem-spinlock.h which is
> used when CONFIG_RWSEM_GENERIC_SPINLOCK=y, trying to access it in MIPS
> architecture causes build error due to type mismatch.
> 
>   error: passing argument 1 of 'atomic_long_read' from incompatible pointer type [-Werror=incompatible-pointer-types]
>   note: expected 'const atomic_long_t * {aka const struct <anonymous> *}' but argument is of type '__s32 * {aka int *}'
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SKAURA.ne.jp>
> Reported-by: kbuild test robot <lkp@intel.com>
> Fixes: 8ee62b1870be8e63 ("locking/rwsem: Convert sem->count to 'atomic_long_t'")
> Cc: stable <stable@vger.kernel.org> # v4.8+
> Cc: Jason Low <jason.low2@hpe.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> ---
>  include/linux/rwsem-spinlock.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/rwsem-spinlock.h b/include/linux/rwsem-spinlock.h
> index e475683..1164965 100644
> --- a/include/linux/rwsem-spinlock.h
> +++ b/include/linux/rwsem-spinlock.h
> @@ -22,7 +22,7 @@
>   * - if wait_list is not empty, then there are processes waiting for the semaphore
>   */
>  struct rw_semaphore {
> -	__s32			count;
> +	atomic_long_t		count;

Uhhh... how does this even build? rwsem-spinlock.c doesn't use
atomic_long primitives to change count.

And the atomic_long count usage is completely private to rwsem-xadd.c,
nothing outside of that should use that field, ever.

Re: [PATCH] locking/rwsem: Convert the other sem->count to 'atomic_long_t'

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 2792 bytes --]

Hi Tetsuo,

I love your patch! Perhaps something to improve:

[auto build test WARNING on tip/locking/core]
[also build test WARNING on v4.18-rc4 next-20180709]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Tetsuo-Handa/locking-rwsem-Convert-the-other-sem-count-to-atomic_long_t/20180710-141553
config: m68k-m5475evb_defconfig (attached as .config)
compiler: m68k-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.2.0 make.cross ARCH=m68k 

All warnings (new ones prefixed by >>):

   In file included from include/linux/notifier.h:15:0,
                    from include/linux/memory_hotplug.h:7,
                    from include/linux/mmzone.h:777,
                    from include/linux/gfp.h:6,
                    from include/linux/idr.h:16,
                    from include/linux/kernfs.h:14,
                    from include/linux/sysfs.h:16,
                    from include/linux/kobject.h:20,
                    from include/linux/pci.h:29,
                    from drivers//pci/search.c:11:
   include/linux/rwsem.h:87:2: warning: missing braces around initializer [-Wmissing-braces]
     { __RWSEM_INIT_COUNT(name),    \
     ^
   include/linux/rwsem.h:94:29: note: in expansion of macro '__RWSEM_INITIALIZER'
     struct rw_semaphore name = __RWSEM_INITIALIZER(name)
                                ^~~~~~~~~~~~~~~~~~~
>> drivers//pci/search.c:17:1: note: in expansion of macro 'DECLARE_RWSEM'
    DECLARE_RWSEM(pci_bus_sem);
    ^~~~~~~~~~~~~

vim +/DECLARE_RWSEM +17 drivers//pci/search.c

^1da177e Linus Torvalds 2005-04-16 @11  #include <linux/pci.h>
5a0e3ad6 Tejun Heo      2010-03-24  12  #include <linux/slab.h>
^1da177e Linus Torvalds 2005-04-16  13  #include <linux/module.h>
^1da177e Linus Torvalds 2005-04-16  14  #include <linux/interrupt.h>
^1da177e Linus Torvalds 2005-04-16  15  #include "pci.h"
^1da177e Linus Torvalds 2005-04-16  16  
d71374da Zhang Yanmin   2006-06-02 @17  DECLARE_RWSEM(pci_bus_sem);
ce29ca3e Amos Kong      2012-05-23  18  EXPORT_SYMBOL_GPL(pci_bus_sem);
ce29ca3e Amos Kong      2012-05-23  19  

:::::: The code at line 17 was first introduced by commit
:::::: d71374dafbba7ec3f67371d3b7e9f6310a588808 [PATCH] PCI: fix race with pci_walk_bus and pci_destroy_dev

:::::: TO: Zhang Yanmin <yanmin.zhang@intel.com>
:::::: CC: Greg Kroah-Hartman <gregkh@suse.de>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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Re: [PATCH] locking/rwsem: Convert the other sem->count to 'atomic_long_t'

[kbuild test robot]

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Hi Tetsuo,

I love your patch! Perhaps something to improve:

[auto build test WARNING on tip/locking/core]
[also build test WARNING on v4.18-rc4 next-20180709]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Tetsuo-Handa/locking-rwsem-Convert-the-other-sem-count-to-atomic_long_t/20180710-141553
config: parisc-c3000_defconfig (attached as .config)
compiler: hppa-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.2.0 make.cross ARCH=parisc 

All warnings (new ones prefixed by >>):

   In file included from include/linux/notifier.h:15:0,
                    from include/linux/memory_hotplug.h:7,
                    from include/linux/mmzone.h:777,
                    from include/linux/gfp.h:6,
                    from include/linux/umh.h:4,
                    from include/linux/kmod.h:22,
                    from include/linux/module.h:13,
                    from drivers/usb/core/hcd-pci.c:7:
   include/linux/rwsem.h:87:2: warning: missing braces around initializer [-Wmissing-braces]
     { __RWSEM_INIT_COUNT(name),    \
     ^
   include/linux/rwsem.h:94:29: note: in expansion of macro '__RWSEM_INITIALIZER'
     struct rw_semaphore name = __RWSEM_INITIALIZER(name)
                                ^~~~~~~~~~~~~~~~~~~
>> drivers/usb/core/hcd-pci.c:31:8: note: in expansion of macro 'DECLARE_RWSEM'
    static DECLARE_RWSEM(companions_rwsem);
           ^~~~~~~~~~~~~

vim +/DECLARE_RWSEM +31 drivers/usb/core/hcd-pci.c

^1da177e4 Linus Torvalds 2005-04-16  @7  #include <linux/module.h>
^1da177e4 Linus Torvalds 2005-04-16   8  #include <linux/pci.h>
21b1861fb David Brownell 2005-11-23   9  #include <linux/usb.h>
27729aadd Eric Lescouet  2010-04-24  10  #include <linux/usb/hcd.h>
21b1861fb David Brownell 2005-11-23  11  
^1da177e4 Linus Torvalds 2005-04-16  12  #include <asm/io.h>
^1da177e4 Linus Torvalds 2005-04-16  13  #include <asm/irq.h>
21b1861fb David Brownell 2005-11-23  14  
21b1861fb David Brownell 2005-11-23  15  #ifdef CONFIG_PPC_PMAC
21b1861fb David Brownell 2005-11-23  16  #include <asm/machdep.h>
21b1861fb David Brownell 2005-11-23  17  #include <asm/pmac_feature.h>
21b1861fb David Brownell 2005-11-23  18  #include <asm/prom.h>
21b1861fb David Brownell 2005-11-23  19  #endif
5f827ea3c David Brownell 2005-09-22  20  
5f827ea3c David Brownell 2005-09-22  21  #include "usb.h"
^1da177e4 Linus Torvalds 2005-04-16  22  
^1da177e4 Linus Torvalds 2005-04-16  23  
c6053ecff David Brownell 2005-04-18  24  /* PCI-based HCs are common, but plenty of non-PCI HCs are used too */
^1da177e4 Linus Torvalds 2005-04-16  25  
05768918b Alan Stern     2013-03-28  26  /*
05768918b Alan Stern     2013-03-28  27   * Coordinate handoffs between EHCI and companion controllers
05768918b Alan Stern     2013-03-28  28   * during EHCI probing and system resume.
6d19c009c Alan Stern     2010-02-12  29   */
6d19c009c Alan Stern     2010-02-12  30  
05768918b Alan Stern     2013-03-28 @31  static DECLARE_RWSEM(companions_rwsem);
6d19c009c Alan Stern     2010-02-12  32  

:::::: The code at line 31 was first introduced by commit
:::::: 05768918b9a122ce21bd55950df5054ff6c57f28 USB: improve port transitions when EHCI starts up

:::::: TO: Alan Stern <stern@rowland.harvard.edu>
:::::: CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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Re: [PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up.

[Tetsuo Handa]

On 2018/07/10 18:30, Peter Zijlstra wrote:
>> diff --git a/include/linux/rwsem-spinlock.h b/include/linux/rwsem-spinlock.h
>> index e475683..1164965 100644
>> --- a/include/linux/rwsem-spinlock.h
>> +++ b/include/linux/rwsem-spinlock.h
>> @@ -22,7 +22,7 @@
>>   * - if wait_list is not empty, then there are processes waiting for the semaphore
>>   */
>>  struct rw_semaphore {
>> -	__s32			count;
>> +	atomic_long_t		count;
> 
> Uhhh... how does this even build? rwsem-spinlock.c doesn't use
> atomic_long primitives to change count.

Sorry, I forgot to build test rwsem-spinlock.c side.

> 
> And the atomic_long count usage is completely private to rwsem-xadd.c,
> nothing outside of that should use that field, ever.
> 

The reason I made above patch is to make
"[PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up." patch
possible to build on x86_64. Although "nothing outside of that should use
that field", I want to check "struct rw_semaphore"->count for isolating
the problem.

Should I update
"[PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up." side
to use "#ifndef CONFIG_RWSEM_GENERIC_SPINLOCK" ?

Re: [PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up.

[Peter Zijlstra]

On Tue, Jul 10, 2018 at 07:48:31PM +0900, Tetsuo Handa wrote:
> Should I update
> "[PATCH] locking/lockdep: Dump state of percpu_rwsem upon hung up." side
> to use "#ifndef CONFIG_RWSEM_GENERIC_SPINLOCK" ?

Since it's a debug patch, who cares if there's a config for which it
doesn't build?

[PATCH v2] locking/lockdep: Dump state of percpu_rwsem upon hung up.

[Tetsuo Handa]

Added "#ifndef CONFIG_RWSEM_GENERIC_SPINLOCK" check.

From 88f979f8f019f32de94327878ef1f7ccb7500321 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@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-kernel@I-love.SAKURA.ne.jp>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Dmitry Vyukov <dvyukov@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