/******************************************************************************/ /* Copyright (c) Tim LaBerge , 2009 */ /* */ /* This program is free software; you can redistribute it and/or modify */ /* it under the terms of the GNU General Public License as published by */ /* the Free Software Foundation; either version 2 of the License, or */ /* (at your option) any later version. */ /* */ /* This program is distributed in the hope that it will be useful, */ /* but WITHOUT ANY WARRANTY; without even the implied warranty of */ /* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See */ /* the GNU General Public License for more details. */ /* */ /* You should have received a copy of the GNU General Public License */ /* along with this program; if not, write to the Free Software Foundation, */ /* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ /* */ /******************************************************************************/ /******************************************************************************/ /* */ /* File: dma_thread_diotest7.c */ /* */ /* Description: The man page for open(2) states the following: */ /* O_DIRECT (Since Linux 2.6.10). Try to minimize cache effects of the I/O */ /* to and from this file. In general this will degrade performance, but it */ /* is useful in special situations, such as when applications do their own */ /* caching. File I/O is done directly to/from user space buffers. The I/O is*/ /* synchronous, that is, at the completion of a read(2) or write(2), data is*/ /* guranteed to have been transferred. Under Linux 2.4 transfer sizes, and */ /* the alignment of user buffer and file offset must all be multiples of */ /* the logical block size of the file system. Under Linux 2.6 alignment to */ /* 512-byte bound-aries suffices. */ /* However, it appears that data corruption may occur when a multithreaded */ /* process reads into a non-page size aligned user buffer. A test program */ /* which reliably reproduces the problem on ext3 and xfs is attached. The */ /* program creates, patterns, reads, and verify a series of files. In the */ /* read phase, a file is opened with O_DIRECT n times, where n is the */ /* number of cpu's. A single buffer large enough to contain the file is */ /* allocated and patterned with data not found in any of the files. The */ /* alignment of the buffer is controlled by a command line option. Each file*/ /* is read in parallel by n threads, where n is the number of cpu's. Thread */ /* 0 reads the first page of data from the file into the first page of the */ /* buffer, thread 1 reads the second page of data in to the second page of */ /* the buffer, and so on. Thread n - 1 reads the remainder of the file into*/ /* the remainder of the buffer. */ /* After a thread reads data into the buffer, it immediately verifies that */ /* the contents of the buffer are correct. If the buffer contains corrupt */ /* data, the thread dumps the data surrounding the corruption and calls */ /* abort(). Otherwise, the thread exits. */ /* Crucially, before the reader threads are dispatched, another thread is */ /* started which calls fork()/msleep() in a loop until all reads are compl- */ /* eted. The child created by fork() does nothing but call exit(0). A comm- */ /* and line option controls whether the buffer is aligned. In the case wh- */ /* ere the buffer is aligned on a page boundary, all is well. In the case */ /* where the buffer is aligned on a page + 512 byte offset, corruption is */ /* seen frequently. */ /* I believe that what is happening is that in the direct IO path, because */ /* the user's buffer is not aligned, some user pages are being mapped twice.*/ /* When a fork() happens in between the calls to map the page, the page will*/ /* be marked as COW. When the second map happens (via get_user_pages()), a */ /* new physical page will be allocated and copied. Thus, there is a race */ /* between the completion of the first read from disk (and write to the user*/ /* page) and get_user_pages() mapping the page for the second time. If the */ /* write does not complete before the page is copied, the user will see */ /* stale data in the first 512 bytes of this page of their buffer. Indeed, */ /* this is corruption most frequently seen. (It's also possible for the race*/ /* to be lost the other way, so that the last 3584 bytes of the page are */ /* stale.) */ /* The attached program (which is a heavily modified version of a program */ /* provided by a customer seeing this problem) reliably reproduces the pro- */ /* blem on any multicore linux machine on both ext3 and xfs, although any */ /* filesystem using the generic blockdev_direct_IO() routine is probably */ /* vulnerable. I've seen a few threads that mention the potential for this */ /* kind of problem, but no definitive solution or workaround (other than */ /* "Don't do that"). */ /* http://marc.info/?l=linux-mm&m=122668235304637&w=2 */ /* */ /* Total Tests: 1 */ /* */ /* Test Name: dma_thread_diotest7 */ /* */ /* Author: Tim LaBerge */ /* */ /* History: Reported - Jan 07 2009 - Li Zefan */ /* Ported - Jan 23 2009 - Subrata */ /* */ /******************************************************************************/ #define _GNU_SOURCE 1 #include #include #include #include #include #include #include #include #include #include #include #include #include "test.h" #include "safe_macros.h" #define FILESIZE (12*1024*1024) #define READSIZE (1024*1024) #define MNT_POINT "mntpoint" #define FILE_BASEPATH MNT_POINT "/_dma_thread_test_%.04d.tmp" #define DIR_MODE (S_IRUSR|S_IWUSR|S_IXUSR|S_IRGRP| \ S_IXGRP|S_IROTH|S_IXOTH) #define FILECOUNT 100 #define PATTERN (0xfa) #define PAGE_SIZE getpagesize() #define MIN_WORKERS 2 #define MAX_WORKERS (READSIZE/PAGE_SIZE) char *TCID = "dma_thread_diotest"; int TST_TOTAL = 1; static void setup(void); static void dma_thread_diotest_verify(void); static void cleanup(void); static void help(void); static unsigned char *buffer; static char *align_str; static int align; static char *workers_str; static int workers; static char *device; static int mount_flag; static option_t options[] = { {"a:", NULL, &align_str}, {"w:", NULL, &workers_str}, {NULL, NULL, NULL} }; static volatile int done; static volatile int tst_result; typedef struct { pthread_t tid; int worker_number; int fd; int offset; int length; int pattern; unsigned char *buffer; } worker_t; static worker_t *worker; static void *worker_thread(void *arg) { int i, k; int nread; worker_t *worker = (worker_t *)arg; int offset = worker->offset; int fd = worker->fd; unsigned char *buffer = worker->buffer; int pattern = worker->pattern; int length = worker->length; if (lseek(fd, offset, SEEK_SET) < 0) { fprintf(stderr, "Failed to lseek to %d on fd %d: %s.\n", offset, fd, strerror(errno)); return (void *) 1; } nread = read(fd, buffer, length); if (nread == -1 || nread != length) { fprintf(stderr, "read failed in worker thread%d: %s", worker->worker_number, strerror(errno)); return (void *) 1; } /* Corruption check */ for (i = 0; i < length; i++) { if (buffer[i] != pattern) { printf("Bad data at 0x%.06x: %p, \n", i, buffer + i); printf("Data dump starting at 0x%.06x:\n", i - 8); printf("Expect 0x%x followed by 0x%x:\n", pattern, PATTERN); for (k = 0; k < 16; k++) { printf("%02x ", buffer[i - 8 + k]); if (k == 7) { printf("\n"); } } printf("\n"); tst_result = 1; return NULL; } } return NULL; } static void *fork_thread(void *arg) { pid_t pid; (void) arg; while (!done) { pid = tst_fork(); if (pid == 0) { exit(0); } else if (pid < 0) { fprintf(stderr, "Failed to fork child: %s.\n", strerror(errno)); return (void *) 1; } waitpid(pid, NULL, 0); usleep(100); } return NULL; } int main(int argc, char *argv[]) { int i, lc; workers = sysconf(_SC_NPROCESSORS_ONLN); if (workers > MAX_WORKERS) workers = MAX_WORKERS; tst_parse_opts(argc, argv, options, help); setup(); for (lc = 0; TEST_LOOPING(lc); lc++) { tst_count = 0; for (i = 0; i < TST_TOTAL; i++) dma_thread_diotest_verify(); } cleanup(); tst_exit(); } static void dma_thread_diotest_verify(void) { int n, j, offset, rc; void *retval; char filename[PATH_MAX]; pthread_t fork_tid; tst_result = 0; for (n = 1; n <= FILECOUNT; n++) { snprintf(filename, sizeof(filename), FILE_BASEPATH, n); for (j = 0; j < workers; j++) { worker[j].fd = SAFE_OPEN(cleanup, filename, O_RDONLY | O_DIRECT); worker[j].pattern = n; } tst_resm(TINFO, "Reading file %d.", n); for (offset = 0; offset < FILESIZE; offset += READSIZE) { memset(buffer, PATTERN, READSIZE + align); for (j = 0; j < workers; j++) { worker[j].offset = offset + j * PAGE_SIZE; worker[j].buffer = buffer + align + j * PAGE_SIZE; worker[j].length = PAGE_SIZE; } /* The final worker reads whatever is left over. */ worker[workers - 1].length = READSIZE - PAGE_SIZE * (workers - 1); done = 0; rc = pthread_create(&fork_tid, NULL, fork_thread, NULL); if (rc != 0) { tst_brkm(TBROK, cleanup, "pthread_create " "failed: %s", strerror(rc)); } for (j = 0; j < workers; j++) { rc = pthread_create(&worker[j].tid, NULL, worker_thread, worker + j); if (rc != 0) { tst_brkm(TBROK, cleanup, "Can't create" "worker thread %d: %s", j, strerror(rc)); } } for (j = 0; j < workers; j++) { rc = pthread_join(worker[j].tid, &retval); if (rc != 0) { tst_brkm(TBROK, cleanup, "Failed to " "join worker thread %d: %s.", j, strerror(rc)); } if ((intptr_t)retval != 0) { tst_brkm(TBROK, cleanup, "there is" "some errors in worker[%d]," "return value: %ld", j, (intptr_t)retval); } } /* Let the fork thread know it's ok to exit */ done = 1; rc = pthread_join(fork_tid, &retval); if (rc != 0) { tst_brkm(TBROK, cleanup, "Failed to join fork thread: %s.", strerror(rc)); } if ((intptr_t)retval != 0) { tst_brkm(TBROK, cleanup, "fork() failed in fork thread:" "return value: %ld", (intptr_t)retval); } } /* Close the fd's for the next file. */ for (j = 0; j < workers; j++) SAFE_CLOSE(cleanup, worker[j].fd); if (tst_result) break; } if (tst_result) tst_resm(TFAIL, "data corruption is detected"); else tst_resm(TPASS, "data corruption is not detected"); } static void setup(void) { char filename[PATH_MAX]; int n, j, fd, directflag = 1; long type; if (align_str) { align = atoi(align_str); if (align < 0 || align > PAGE_SIZE) tst_brkm(TCONF, NULL, "Bad alignment %d.", align); } tst_resm(TINFO, "using alignment %d", align); if (workers_str) { workers = atoi(workers_str); if (workers < MIN_WORKERS || workers > MAX_WORKERS) { tst_brkm(TCONF, NULL, "Worker count %d not between " "%d and %d, inclusive", workers, MIN_WORKERS, MAX_WORKERS); } } tst_resm(TINFO, "using %d workers.", workers); tst_sig(FORK, DEF_HANDLER, NULL); tst_require_root(); TEST_PAUSE; tst_tmpdir(); /* * Some file systems may not implement the O_DIRECT flag and open() will * fail with EINVAL if it is used. So add this check for current * filesystem current directory is in, if not supported, we choose to * have this test in LTP_BIG_DEV and mkfs it as ext3. */ fd = open("testfile", O_CREAT | O_DIRECT, 0644); if (fd < 0 && errno == EINVAL) { type = tst_fs_type(NULL, "."); tst_resm(TINFO, "O_DIRECT flag is not supported on %s " "filesystem", tst_fs_type_name(type)); directflag = 0; } else if (fd > 0) { SAFE_CLOSE(NULL, fd); } SAFE_MKDIR(cleanup, MNT_POINT, DIR_MODE); /* * verify whether the current directory has enough free space, * if it is not satisfied, we will use the LTP_BIG_DEV, which * will be exported by runltp with "-z" option. */ if (!directflag || !tst_fs_has_free(NULL, ".", 1300, TST_MB)) { device = getenv("LTP_BIG_DEV"); if (device == NULL) { tst_brkm(TCONF, NULL, "you must specify a big blockdevice(>1.3G)"); } else { tst_mkfs(NULL, device, "ext3", NULL, NULL); } if (mount(device, MNT_POINT, "ext3", 0, NULL) < 0) { tst_brkm(TBROK | TERRNO, NULL, "mount device:%s failed", device); } mount_flag = 1; } worker = SAFE_MALLOC(cleanup, workers * sizeof(worker_t)); for (j = 0; j < workers; j++) worker[j].worker_number = j; for (n = 1; n <= FILECOUNT; n++) { snprintf(filename, sizeof(filename), FILE_BASEPATH, n); if (tst_fill_file(filename, n, FILESIZE, 1)) { tst_brkm(TBROK, cleanup, "failed to create file: %s", filename); } } if (posix_memalign((void **)&buffer, PAGE_SIZE, READSIZE + align) != 0) tst_brkm(TBROK, cleanup, "call posix_memalign failed"); } static void cleanup(void) { free(buffer); if (mount_flag && tst_umount(MNT_POINT) < 0) tst_resm(TWARN | TERRNO, "umount device:%s failed", device); free(worker); tst_rmdir(); } static void help(void) { printf("-a align read buffer to offset .\n"); printf("-w number of worker threads, 2 (default) to %d," " defaults to number of cores.\n", MAX_WORKERS); }