On 2012-07-31 21:06, Jens Axboe wrote: > On 2012-06-20 01:05, Erik Lattimore wrote: >> Lately it seems like we've been hitting this more frequently, so I figured I'd file a bug. Fio starts up a thread running the function disk_thread_main, which periodically calls update_io_ticks, which calls update_io_tick_disk on each entry in a circular linked list. The function disk_thread_main returns when the global variable "threads" is set to null, but it's only checked a couple of times in the loop. >> >> The main thread runs the test and exits, and has registered an atexit handler free_shm. This routine sets "threads" to null and frees up storage, including the storage where the linked list used by update_io_ticks is stored. >> >> Occasionally, somehow, update_io_tick_disk winds up getting called with a null pointer and crashing. The problem may be exacerbated when memory is tight. Here's the backtrace of the core dump: >> >> Program terminated with signal 11, Segmentation fault. >> #0 update_io_tick_disk (du=<optimized out>) at diskutil.c:80 >> 80 if (!du->users) >> (gdb) t apply all bt >> >> Thread 2 (Thread 0x7faab680b700 (LWP 23148)): >> #0 0x00007faab58df377 in shmdt () from /lib64/libc.so.6 >> #1 0x000000000040b98d in free_shm () at init.c:231 >> #2 0x00007faab583b7f5 in __run_exit_handlers () from /lib64/libc.so.6 >> #3 0x00007faab583b845 in exit () from /lib64/libc.so.6 >> #4 0x00007faab5824c3d in __libc_start_main () from /lib64/libc.so.6 >> #5 0x0000000000408ed9 in _start () >> >> Thread 1 (Thread 0x7faab32dd700 (LWP 23149)): >> #0 update_io_tick_disk (du=<optimized out>) at diskutil.c:80 >> #1 update_io_ticks () at diskutil.c:114 >> #2 0x000000000043b303 in disk_thread_main (data=<optimized out>) at backend.c:1589 >> #3 0x00007faab61907b6 in start_thread () from /lib64/libpthread.so.0 >> #4 0x00007faab58dd9cd in clone () from /lib64/libc.so.6 >> #5 0x0000000000000000 in ?? () >> (gdb) q-- > > This is clearly a race in how the disk util thread is shut down and the > structures freed. I'll take a look at a fix. It would be useful if you > told me how you are hitting this most easily, as I don't recall seeing > it. Would make me more confident in a fix. > > Also, are you sure it's threads == NULL, and not the du's themselves > being freed? They are in separate storage. It might be a good idea to > have diskutil.c:free_disk_util() signal and wait for the disk util > thread to shutdown before going further. Can you reproduce with this patch? diff --git a/backend.c b/backend.c index e1dc0ac..03d35df 100644 --- a/backend.c +++ b/backend.c @@ -50,6 +50,8 @@ #include "server.h" static pthread_t disk_util_thread; +struct fio_mutex *disk_util_mutex; +int disk_util_exit = 0; static struct fio_mutex *startup_mutex; static struct fio_mutex *writeout_mutex; static struct flist_head *cgroup_list; @@ -1592,9 +1594,9 @@ static void *disk_thread_main(void *data) { fio_mutex_up(startup_mutex); - while (threads) { + while (threads && !disk_util_exit) { usleep(DISK_UTIL_MSEC * 1000); - if (!threads) + if (!threads || disk_util_exit) break; update_io_ticks(); @@ -1602,6 +1604,7 @@ static void *disk_thread_main(void *data) print_thread_status(); } + fio_mutex_up(disk_util_mutex); return NULL; } @@ -1609,15 +1612,19 @@ static int create_disk_util_thread(void) { int ret; + disk_util_mutex = fio_mutex_init(0); + ret = pthread_create(&disk_util_thread, NULL, disk_thread_main, NULL); if (ret) { log_err("Can't create disk util thread: %s\n", strerror(ret)); + fio_mutex_remove(disk_util_mutex); return 1; } ret = pthread_detach(disk_util_thread); if (ret) { log_err("Can't detatch disk util thread: %s\n", strerror(ret)); + fio_mutex_remove(disk_util_mutex); return 1; } diff --git a/diskutil.c b/diskutil.c index feb8852..36b381f 100644 --- a/diskutil.c +++ b/diskutil.c @@ -521,6 +521,9 @@ void free_disk_util(void) { struct disk_util *du; + disk_util_exit = 1; + fio_mutex_down(disk_util_mutex); + while (!flist_empty(&disk_list)) { du = flist_entry(disk_list.next, struct disk_util, list); flist_del(&du->list); @@ -528,6 +531,7 @@ void free_disk_util(void) } last_majdev = last_mindev = -1; + fio_mutex_remove(disk_util_mutex); } void print_disk_util(struct disk_util_stat *dus, struct disk_util_agg *agg, diff --git a/diskutil.h b/diskutil.h index 5a9b079..c7212fa 100644 --- a/diskutil.h +++ b/diskutil.h @@ -3,6 +3,9 @@ #define FIO_DU_NAME_SZ 64 +extern struct fio_mutex *disk_util_mutex; +extern int disk_util_exit; + /* * Disk utils as read in /sys/block/<dev>/stat */ @@ -106,7 +109,10 @@ extern void update_io_ticks(void); #else #define print_disk_util(dus, agg, terse) #define show_disk_util(terse) -#define free_disk_util() +static inline void free_disk_util(void) +{ + fio_mutex_remove(disk_util_mutex); +} #define init_disk_util(td) #define update_io_ticks() #endif -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html