[LTP] [PATCH] kernel/mem/mtest06/mmap1.c: Update the synchronization logic

[LTP] [PATCH] kernel/mem/mtest06/mmap1.c: Update the synchronization logic

[shuang.qiu]

From: Shuang Qiu <shuang.qiu@oracle.com>

Currently in mmap1.c,the reader and writer cannot synchronize with each other.
Added one more lock and update the logic a little to make it work.

Signed-off-by: Shuang Qiu <shuang.qiu@oracle.com>
---
 testcases/kernel/mem/mtest06/mmap1.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/testcases/kernel/mem/mtest06/mmap1.c b/testcases/kernel/mem/mtest06/mmap1.c
index cd1127f..6bdbf75 100644
--- a/testcases/kernel/mem/mtest06/mmap1.c
+++ b/testcases/kernel/mem/mtest06/mmap1.c
@@ -65,6 +65,7 @@ static int verbose_print = 0;
 static char *volatile map_address;
 static jmp_buf jmpbuf;
 static volatile char read_lock = 0;
+static volatile char write_lock = 0;
 
 char *TCID = "mmap1";
 int TST_TOTAL = 1;
@@ -157,6 +158,7 @@ void *map_write_unmap(void *ptr)
 
 		while (read_lock)
 			sched_yield();
+		read_lock = 1;
 
 		sigfillset(&sa.sa_mask);
 		sigdelset(&sa.sa_mask, SIGSEGV);
@@ -197,6 +199,7 @@ void *map_write_unmap(void *ptr)
 			perror("map_write_unmap(): mmap()");
 			pthread_exit((void *)1);
 		}
+		write_lock = 0;
 	}
 
 	pthread_exit((void *)0);
@@ -218,6 +221,9 @@ void *read_mem(void *ptr)
 
 	for (i = 0; i < args[2]; i++) {
 
+		while (write_lock)
+			sched_yield();
+		write_lock = 1;
 		if (verbose_print)
 			tst_resm(TINFO, "read_mem() in while loop %ld times "
 				 "to go %ld times", i, args[2]);
@@ -229,20 +235,17 @@ void *read_mem(void *ptr)
 					 "a read after an unmap");
 		} else {
 			if (verbose_print) {
-				read_lock = 1;
 				tst_resm(TINFO,
 					 "read_mem(): content of memory: %s",
 					 (char *)map_address);
-				read_lock = 0;
 			}
 			for (j = 0; j < args[1]; j++) {
-				read_lock = 1;
 				if (map_address[j] != 'a')
 					pthread_exit((void *)-1);
-				read_lock = 0;
 				if (random() % 2)
 					sched_yield();
 			}
+			read_lock = 0;
 		}
 	}
 
-- 
1.7.9.5


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Re: [LTP] [PATCH] kernel/mem/mtest06/mmap1.c: Update the synchronization logic

[chrubis]

Hi!
> Currently in mmap1.c,the reader and writer cannot synchronize with each other.
> Added one more lock and update the logic a little to make it work.
> 
> Signed-off-by: Shuang Qiu <shuang.qiu@oracle.com>
> ---
>  testcases/kernel/mem/mtest06/mmap1.c |   11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/testcases/kernel/mem/mtest06/mmap1.c b/testcases/kernel/mem/mtest06/mmap1.c
> index cd1127f..6bdbf75 100644
> --- a/testcases/kernel/mem/mtest06/mmap1.c
> +++ b/testcases/kernel/mem/mtest06/mmap1.c
> @@ -65,6 +65,7 @@ static int verbose_print = 0;
>  static char *volatile map_address;
>  static jmp_buf jmpbuf;
>  static volatile char read_lock = 0;
> +static volatile char write_lock = 0;
>  
>  char *TCID = "mmap1";
>  int TST_TOTAL = 1;
> @@ -157,6 +158,7 @@ void *map_write_unmap(void *ptr)
>  
>  		while (read_lock)
>  			sched_yield();
> +		read_lock = 1;

This is obviously wrong because combined with the removal of the
read_lock = 1 from the read_mem() thread you just disabled the writer
thread entirely.

>  		sigfillset(&sa.sa_mask);
>  		sigdelset(&sa.sa_mask, SIGSEGV);
> @@ -197,6 +199,7 @@ void *map_write_unmap(void *ptr)
>  			perror("map_write_unmap(): mmap()");
>  			pthread_exit((void *)1);
>  		}
> +		write_lock = 0;
>  	}
>  
>  	pthread_exit((void *)0);
> @@ -218,6 +221,9 @@ void *read_mem(void *ptr)
>  
>  	for (i = 0; i < args[2]; i++) {
>  
> +		while (write_lock)
> +			sched_yield();
> +		write_lock = 1;

The same here, this disables the thread.


Can you describe precisely what race condition are you trying to fix?

-- 
Cyril Hrubis
chrubis@suse.cz

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