generic: Test races between processes doing mmap writes

Add test which spawns two processes both writing one file via mmap.
Then to the test when processes first prefault the file by reading it
via mmap. This is mainly interesting to uncover races in DAX fault
handling.

Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

src/holetest.c

@@ -61,6 +61,7 @@
 #include <pthread.h>
 #include <string.h>
 #include <getopt.h>
+#include <sys/wait.h>
 
 #define THREADS 2
 
@@ -68,6 +69,26 @@ long page_size;
 long page_offs[THREADS];
 int use_wr[THREADS];
 int prefault = 0;
+int use_fork = 0;
+
+uint64_t get_id(void)
+{
+	if (!use_fork)
+		return (uint64_t) pthread_self();
+	return getpid();
+}
+
+void prefault_mapping(char *addr, long npages)
+{
+	long i;
+
+	for (i = 0; i < npages; i++) {
+		if (addr[i * page_size] != 0) {
+			fprintf(stderr, "Prefaulting found non-zero value in "
+				"page %ld: %d\n", i, (int)addr[i * page_size]);
+		}
+	}
+}
 
 void *pt_page_marker(void *args)
 {
@@ -75,7 +96,10 @@ void *pt_page_marker(void *args)
 	char *va = (char *)a[1];
 	long npages = (long)a[2];
 	long pgoff = (long)a[3];
-	uint64_t tid = (uint64_t)pthread_self();
+	uint64_t tid = get_id();
+
+	if (prefault && use_fork)
+		prefault_mapping(va, npages);
 
 	va += pgoff;
 
@@ -92,7 +116,7 @@ void *pt_write_marker(void *args)
 	int fd = (long)a[0];
 	long npages = (long)a[2];
 	long pgoff = (long)a[3];
-	uint64_t tid = (uint64_t)pthread_self();
+	uint64_t tid = get_id();
 	long i;
 
 	/* mark pages */
@@ -123,15 +147,8 @@ int test_this(int fd, loff_t sz)
 		exit(20);
 	}
 
-	if (prefault) {
+	if (prefault && !use_fork)
-		for (i = 0; i < npages; i++) {
+		prefault_mapping(vastart, npages);
-			if (vastart[i * page_size] != 0) {
-				fprintf(stderr, "Prefaulting found non-zero "
-					"value in page %d: %d\n", i,
-					vastart[i * page_size]);
-			}
-		}
-	}
 
 	/* prepare the thread args */
 	for (i = 0; i < THREADS; i++) {
@@ -142,20 +159,49 @@ int test_this(int fd, loff_t sz)
 	}
 
 	for (i = 0; i < THREADS; i++) {
-		/* start two threads */
+		if (!use_fork) {
-		if (pthread_create(&t[i], NULL,
+			/* start two threads */
+			if (pthread_create(&t[i], NULL,
 				   use_wr[i] ? pt_write_marker : pt_page_marker,
 				   &targs[i])) {
-			perror("pthread_create");
+				perror("pthread_create");
-			exit(21);
+				exit(21);
+			}
+			tid[i] = (uint64_t)t[i];
+			printf("INFO: thread %d created\n", i);
+		} else {
+			/*
+			 * Flush stdout before fork, otherwise some lines get
+			 * duplicated... ?!?!?
+			 */
+			fflush(stdout);
+			tid[i] = fork();
+			if (tid[i] < 0) {
+				int j;
+
+				perror("fork");
+				for (j = 0; j < i; j++)
+					waitpid(tid[j], NULL, 0);
+				exit(21);
+			}
+			/* Child? */
+			if (!tid[i]) {
+				if (use_wr[i])
+					pt_write_marker(&targs[i]);
+				else
+					pt_page_marker(&targs[i]);
+				exit(0);
+			}
+			printf("INFO: process %d created\n", i);
 		}
-		tid[i] = (uint64_t)t[i];
-		printf("INFO: thread %d created\n", i);
 	}
 
 	/* wait for them to finish */
 	for (i = 0; i < THREADS; i++)
-		pthread_join(t[i], NULL);
+		if (!use_fork)
+			pthread_join(t[i], NULL);
+		else
+			waitpid(tid[i], NULL, 0);
 
 	/* check markers on each page */
 	errcnt = 0;
@@ -196,7 +242,7 @@ int main(int argc, char **argv)
 	for (i = 1; i < THREADS; i++)
 		page_offs[i] = page_offs[i-1] + step;
 
-	while ((opt = getopt(argc, argv, "fwr")) > 0) {
+	while ((opt = getopt(argc, argv, "fwrF")) > 0) {
 		switch (opt) {
 		case 'f':
 			/* ignore errors */
@@ -210,6 +256,10 @@ int main(int argc, char **argv)
 			/* prefault mmapped area by reading it */
 			prefault = 1;
 			break;
+		case 'F':
+			/* create processes instead of threads */
+			use_fork = 1;
+			break;
 		default:
 			fprintf(stderr, "ERROR: Unknown option character.\n");
 			exit(1);
@@ -217,7 +267,7 @@ int main(int argc, char **argv)
 	}
 
 	if (optind != argc - 2) {
-		fprintf(stderr, "ERROR: usage: holetest [-fwr] "
+		fprintf(stderr, "ERROR: usage: holetest [-fwrF] "
 			"FILENAME FILESIZEinMB\n");
 		exit(1);
 	}

tests/generic/345

@@ -0,0 +1,59 @@
+#! /bin/bash
+# FSQA Test No. 345
+#
+# Test races between mmap from racing processes with and without prefaulting.
+#
+#-----------------------------------------------------------------------
+#
+# Copyright (C) 2016 SUSE Linux Products GmbH. All Rights Reserved.
+# Author: Jan Kara <jack@suse.cz>
+#
+# 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.
+#
+# This program is distributed in the hope that it would 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 the Free Software Foundation,
+# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#-----------------------------------------------------------------------
+#
+
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+}
+
+# get standard environment and checks
+. ./common/rc
+
+# real QA test starts here
+_supported_fs generic
+_supported_os Linux
+_require_scratch
+_require_test_program "holetest"
+
+rm -f $seqres.full
+
+_scratch_mkfs >>$seqres.full 2>&1
+_scratch_mount
+
+src/holetest -f -F $SCRATCH_MNT/testfile 16
+src/holetest -f -F $SCRATCH_MNT/testfile 256
+src/holetest -f -F -r $SCRATCH_MNT/testfile 16
+src/holetest -f -F -r $SCRATCH_MNT/testfile 256
+
+status=0
+exit

tests/generic/345.out

@@ -0,0 +1,73 @@
+QA output created by 345
+
+INFO: zero-filled test...
+INFO: sz = 16777216
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected
+
+INFO: posix_fallocate test...
+INFO: sz = 16777216
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected
+
+INFO: ftruncate test...
+INFO: sz = 16777216
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected
+
+INFO: zero-filled test...
+INFO: sz = 268435456
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected
+
+INFO: posix_fallocate test...
+INFO: sz = 268435456
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected
+
+INFO: ftruncate test...
+INFO: sz = 268435456
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected
+
+INFO: zero-filled test...
+INFO: sz = 16777216
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected
+
+INFO: posix_fallocate test...
+INFO: sz = 16777216
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected
+
+INFO: ftruncate test...
+INFO: sz = 16777216
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected
+
+INFO: zero-filled test...
+INFO: sz = 268435456
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected
+
+INFO: posix_fallocate test...
+INFO: sz = 268435456
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected
+
+INFO: ftruncate test...
+INFO: sz = 268435456
+INFO: process 0 created
+INFO: process 1 created
+INFO: 0 error(s) detected

tests/generic/group

@@ -347,6 +347,7 @@
 342 auto quick metadata
 343 auto quick metadata
 344 auto
+345 auto
 346 auto
 705 blockdev quick rw
 706 blockdev quick rw