btrfs-progs: convert: Fix data race when reporting progress

The status display was reading the state while the task was updating
it. Use a mutex to prevent the race.

This race was detected using ThreadSanitizer and
misc-tests/005-convert-progress-thread-crash.

==================
WARNING: ThreadSanitizer: data race
  Write of size 8 by main thread:
    #0 ext2_copy_inodes btrfs-progs/convert/source-ext2.c:853
    #1 copy_inodes btrfs-progs/convert/main.c:145
    #2 do_convert btrfs-progs/convert/main.c:1297
    #3 main btrfs-progs/convert/main.c:1924

  Previous read of size 8 by thread T1:
    #0 print_copied_inodes btrfs-progs/convert/main.c:124

  Location is stack of main thread.

  Thread T1 (running) created by main thread at:
    #0 pthread_create <null>
    #1 task_start btrfs-progs/task-utils.c:50
    #2 do_convert btrfs-progs/convert/main.c:1295
    #3 main btrfs-progs/convert/main.c:1924

SUMMARY: ThreadSanitizer: data race
btrfs-progs/convert/source-ext2.c:853 in ext2_copy_inodes

Signed-off-by: Adam Buchbinder <abuchbinder@google.com>
Signed-off-by: David Sterba <dsterba@suse.com>

convert/main.c

@@ -88,6 +88,7 @@
 #include <fcntl.h>
 #include <unistd.h>
 #include <getopt.h>
+#include <pthread.h>
 #include <stdbool.h>
 
 #include "ctree.h"
@@ -119,10 +120,12 @@ static void *print_copied_inodes(void *p)
 	task_period_start(priv->info, 1000 /* 1s */);
 	while (1) {
 		count++;
+		pthread_mutex_lock(&priv->mutex);
 		printf("copy inodes [%c] [%10llu/%10llu]\r",
 		       work_indicator[count % 4],
 		       (unsigned long long)priv->cur_copy_inodes,
 		       (unsigned long long)priv->max_copy_inodes);
+		pthread_mutex_unlock(&priv->mutex);
 		fflush(stdout);
 		task_period_wait(priv->info);
 	}
@@ -1287,6 +1290,11 @@ static int do_convert(const char *devname, u32 convert_flags, u32 nodesize,
 	}
 
 	printf("creating btrfs metadata");
+	ret = pthread_mutex_init(&ctx.mutex, NULL);
+	if (ret) {
+		error("failed to initialize mutex: %d", ret);
+		goto fail;
+	}
 	ctx.max_copy_inodes = (cctx.inodes_count - cctx.free_inodes_count);
 	ctx.cur_copy_inodes = 0;
 

convert/source-ext2.c

@@ -18,6 +18,7 @@
 
 #include "kerncompat.h"
 #include <linux/limits.h>
+#include <pthread.h>
 #include "disk-io.h"
 #include "transaction.h"
 #include "utils.h"
@@ -850,7 +851,9 @@ static int ext2_copy_inodes(struct btrfs_convert_context *cctx,
 		ret = ext2_copy_single_inode(trans, root,
 					objectid, ext2_fs, ext2_ino,
 					&ext2_inode, convert_flags);
+		pthread_mutex_lock(&p->mutex);
 		p->cur_copy_inodes++;
+		pthread_mutex_unlock(&p->mutex);
 		if (ret)
 			return ret;
 		if (trans->blocks_used >= 4096) {

convert/source-fs.h

@@ -18,6 +18,8 @@
 #define __BTRFS_CONVERT_SOURCE_FS_H__
 
 #include "kerncompat.h"
+#include <pthread.h>
+
 
 #define CONV_IMAGE_SUBVOL_OBJECTID BTRFS_FIRST_FREE_OBJECTID
 
@@ -37,6 +39,7 @@ extern const struct simple_range btrfs_reserved_ranges[3];
 struct task_info;
 
 struct task_ctx {
+	pthread_mutex_t mutex;
 	u64 max_copy_inodes;
 	u64 cur_copy_inodes;
 	struct task_info *info;