Messages in this thread | | | From | Shan Hai <> | Subject | [PATCH 0/1] Fixup write permission of TLB on powerpc e500 core | Date | Fri, 15 Jul 2011 16:07:17 +0800 |
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The following test case could reveal a bug in the futex_lock_pi()
BUG: On FUTEX_LOCK_PI, there is a infinite loop in the futex_lock_pi() on Powerpc e500 core. Cause: The linux kernel on the e500 core has no write permission on the COW page, refer the head comment of the following test code.
ftrace on test case: [000] 353.990181: futex_lock_pi_atomic <-futex_lock_pi [000] 353.990185: cmpxchg_futex_value_locked <-futex_lock_pi_atomic [snip] [000] 353.990191: do_page_fault <-handle_page_fault [000] 353.990192: bad_page_fault <-handle_page_fault [000] 353.990193: search_exception_tables <-bad_page_fault [snip] [000] 353.990199: get_user_pages <-fault_in_user_writeable [snip] [000] 353.990208: mark_page_accessed <-follow_page [000] 353.990222: futex_lock_pi_atomic <-futex_lock_pi [snip] [000] 353.990230: cmpxchg_futex_value_locked <-futex_lock_pi_atomic [ a loop occures here ]
/* * A test case for revealing an infinite loop in the futex_lock_pi(). * - there are 2 processes, parent and a child * - the parent process allocates and initializes a pthread_mutex MUTEX in a * shared memory region * - the parent process holds the MUTEX and do long time computing * - the child process tries to hold the MUTEX during the parent holding it and * traps into the kernel for waiting on the MUTEX because of contention * - the kernel loops in futex_lock_pi() * - result of 'top' command reveals that the system usage of CPU is 100% */
#include <stdio.h> #include <stdlib.h> #include <sys/ipc.h> #include <sys/shm.h> #include <errno.h> #include <pthread.h> #include <string.h> #include <signal.h> #include <fcntl.h> #include <sys/types.h> #include <sys/mman.h>
enum { SHM_INIT, SHM_GET }; enum { PARENT, CHILD };
#define FIXED_MMAP_ADDR 0x20000000 #define MMAP_SIZE 0x2000000
static int shmid; static char shm_name[100]; static int sleep_period = 100000;
void * shmem_init(int flag) { int start = FIXED_MMAP_ADDR; int memory_size = MMAP_SIZE; int mode = 0666; void *addr; int ret;
sprintf(shm_name, "/shmem_1234");
shmid = shm_open (shm_name, O_RDWR | O_EXCL | O_CREAT | O_TRUNC, mode);
if (shmid < 0) { if (errno == EEXIST) { printf ("shm_open: %s\n", strerror(errno)); shmid = shm_open (shm_name, O_RDWR, mode); } else { printf("failed to shm_open, err=%s\n", strerror(errno)); return NULL; } }
ret = fcntl (shmid, F_SETFD, FD_CLOEXEC); if (ret < 0) { printf("fcntl: %s\n", strerror(errno)); return NULL; }
ret = ftruncate (shmid, memory_size); if (ret < 0) { printf("ftruncate: %s\n", strerror(errno)); return NULL; }
addr = mmap ((void *)start, memory_size, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED, shmid, 0);
if (addr == MAP_FAILED) { printf ("mmap: %s\n", strerror(errno)); close (shmid); shm_unlink (shm_name); return NULL; } if (flag == SHM_INIT) memset(addr, 0, memory_size); return (void *)start; }
pthread_mutex_t * shmem_mutex_init(int flag) { pthread_mutex_t * pmutex = (pthread_mutex_t *)shmem_init(flag); pthread_mutexattr_t attr;
if (flag == SHM_INIT) { pthread_mutexattr_init (&attr); pthread_mutexattr_setpshared (&attr, PTHREAD_PROCESS_SHARED); pthread_mutexattr_setprotocol (&attr, PTHREAD_PRIO_INHERIT); pthread_mutexattr_setrobust_np (&attr, PTHREAD_MUTEX_STALLED_NP); pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_ERRORCHECK); if (pthread_mutex_init (pmutex, &attr) != 0) { printf("Init mutex failed, err=%s\n", strerror(errno)); pthread_mutexattr_destroy (&attr); return NULL; } }
return pmutex; }
void long_running_task(int flag) { static int counter = 0;
if (flag == PARENT) usleep(5*sleep_period); else usleep(3*sleep_period);
counter = (counter + 1) % 100; printf("%d: completed %d computing\n", getpid(), counter); }
void sig_handler(int signum) { close(shmid); shm_unlink(shm_name); exit(0); }
int main(int argc, char *argv[]) { pthread_mutex_t *mutex_parent, *mutex_child;
signal(SIGUSR1, sig_handler);
if (fork()) { /* parent process */ if ((mutex_parent = shmem_mutex_init(SHM_INIT)) == NULL) { printf("failed to get the shmem_mutex\n"); exit(-1); } while (1) { printf("%d: try to hold the lock\n", getpid()); pthread_mutex_lock(mutex_parent); printf("%d: got the lock\n", getpid()); long_running_task(PARENT); pthread_mutex_unlock(mutex_parent); printf("%d: released the lock\n", getpid()); } } else { /* child process */ usleep(sleep_period); if ((mutex_child = shmem_mutex_init(SHM_GET)) == NULL) { printf("failed to get the shmem_mutex\n"); exit(-1); } while (1) { printf("%d: try to hold the lock\n", getpid()); pthread_mutex_lock(mutex_child); printf("%d: got the lock\n", getpid()); long_running_task(CHILD); pthread_mutex_unlock(mutex_child); printf("%d: released the lock\n", getpid()); } }
return 0; }
--- arch/powerpc/include/asm/futex.h | 11 ++++++++++- arch/powerpc/include/asm/tlb.h | 25 +++++++++++++++++++++++++ 2 files changed, 35 insertions(+), 1 deletions(-)
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