Btrfs: make filesystem read-only when submitting barrier fails

So far the return code of barrier_all_devices() is ignored, which
means that errors are ignored. The result can be a corrupt
filesystem which is not consistent.
This commit adds code to evaluate the return code of
barrier_all_devices(). The normal btrfs_error() mechanism is used to
switch the filesystem into read-only mode when errors are detected.

In order to decide whether barrier_all_devices() should return
error or success, the number of disks that are allowed to fail the
barrier submission is calculated. This calculation accounts for the
worst RAID level of metadata, system and data. If single, dup or
RAID0 is in use, a single disk error is already considered to be
fatal. Otherwise a single disk error is tolerated.

The calculation of the number of disks that are tolerated to fail
the barrier operation is performed when the filesystem gets mounted,
when a balance operation is started and finished, and when devices
are added or removed.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>

1 files changed, 96 insertions, 13 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index c69995556f61..835523687707 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2505,6 +2505,8 @@ retry_root_backup:
                 printk(KERN_ERR "Failed to read block groups: %d\n", ret);
                 goto fail_block_groups;
         }
+        fs_info->num_tolerated_disk_barrier_failures =
+                btrfs_calc_num_tolerated_disk_barrier_failures(fs_info);
 
         fs_info->cleaner_kthread = kthread_run(cleaner_kthread, tree_root,
                                                "btrfs-cleaner");
@@ -2888,12 +2890,10 @@ static int write_dev_flush(struct btrfs_device *device, int wait)
                         printk_in_rcu("btrfs: disabling barriers on dev %s\n",
                                       rcu_str_deref(device->name));
                         device->nobarriers = 1;
-                }
-                if (!bio_flagged(bio, BIO_UPTODATE)) {
+                } else if (!bio_flagged(bio, BIO_UPTODATE)) {
                         ret = -EIO;
-                        if (!bio_flagged(bio, BIO_EOPNOTSUPP))
-                                btrfs_dev_stat_inc_and_print(device,
-                                        BTRFS_DEV_STAT_FLUSH_ERRS);
+                        btrfs_dev_stat_inc_and_print(device,
+                                BTRFS_DEV_STAT_FLUSH_ERRS);
                 }
 
                 /* drop the reference from the wait == 0 run */
@@ -2932,14 +2932,15 @@ static int barrier_all_devices(struct btrfs_fs_info *info)
 {
         struct list_head *head;
         struct btrfs_device *dev;
-        int errors = 0;
+        int errors_send = 0;
+        int errors_wait = 0;
         int ret;
 
         /* send down all the barriers */
         head = &info->fs_devices->devices;
         list_for_each_entry_rcu(dev, head, dev_list) {
                 if (!dev->bdev) {
-                        errors++;
+                        errors_send++;
                         continue;
                 }
                 if (!dev->in_fs_metadata || !dev->writeable)
@@ -2947,13 +2948,13 @@ static int barrier_all_devices(struct btrfs_fs_info *info)
 
                 ret = write_dev_flush(dev, 0);
                 if (ret)
-                        errors++;
+                        errors_send++;
         }
 
         /* wait for all the barriers */
         list_for_each_entry_rcu(dev, head, dev_list) {
                 if (!dev->bdev) {
-                        errors++;
+                        errors_wait++;
                         continue;
                 }
                 if (!dev->in_fs_metadata || !dev->writeable)
@@ -2961,13 +2962,87 @@ static int barrier_all_devices(struct btrfs_fs_info *info)
 
                 ret = write_dev_flush(dev, 1);
                 if (ret)
-                        errors++;
+                        errors_wait++;
         }
-        if (errors)
+        if (errors_send > info->num_tolerated_disk_barrier_failures ||
+            errors_wait > info->num_tolerated_disk_barrier_failures)
                 return -EIO;
         return 0;
 }
 
+int btrfs_calc_num_tolerated_disk_barrier_failures(
+        struct btrfs_fs_info *fs_info)
+{
+        struct btrfs_ioctl_space_info space;
+        struct btrfs_space_info *sinfo;
+        u64 types[] = {BTRFS_BLOCK_GROUP_DATA,
+                       BTRFS_BLOCK_GROUP_SYSTEM,
+                       BTRFS_BLOCK_GROUP_METADATA,
+                       BTRFS_BLOCK_GROUP_DATA | BTRFS_BLOCK_GROUP_METADATA};
+        int num_types = 4;
+        int i;
+        int c;
+        int num_tolerated_disk_barrier_failures =
+                (int)fs_info->fs_devices->num_devices;
+
+        for (i = 0; i < num_types; i++) {
+                struct btrfs_space_info *tmp;
+
+                sinfo = NULL;
+                rcu_read_lock();
+                list_for_each_entry_rcu(tmp, &fs_info->space_info, list) {
+                        if (tmp->flags == types[i]) {
+                                sinfo = tmp;
+                                break;
+                        }
+                }
+                rcu_read_unlock();
+
+                if (!sinfo)
+                        continue;
+
+                down_read(&sinfo->groups_sem);
+                for (c = 0; c < BTRFS_NR_RAID_TYPES; c++) {
+                        if (!list_empty(&sinfo->block_groups[c])) {
+                                u64 flags;
+
+                                btrfs_get_block_group_info(
+                                        &sinfo->block_groups[c], &space);
+                                if (space.total_bytes == 0 ||
+                                    space.used_bytes == 0)
+                                        continue;
+                                flags = space.flags;
+                                /*
+                                 * return
+                                 * 0: if dup, single or RAID0 is configured for
+                                 *    any of metadata, system or data, else
+                                 * 1: if RAID5 is configured, or if RAID1 or
+                                 *    RAID10 is configured and only two mirrors
+                                 *    are used, else
+                                 * 2: if RAID6 is configured, else
+                                 * num_mirrors - 1: if RAID1 or RAID10 is
+                                 *                  configured and more than
+                                 *                  2 mirrors are used.
+                                 */
+                                if (num_tolerated_disk_barrier_failures > 0 &&
+                                    ((flags & (BTRFS_BLOCK_GROUP_DUP |
+                                               BTRFS_BLOCK_GROUP_RAID0)) ||
+                                     ((flags & BTRFS_BLOCK_GROUP_PROFILE_MASK)
+                                      == 0)))
+                                        num_tolerated_disk_barrier_failures = 0;
+                                else if (num_tolerated_disk_barrier_failures > 1
+                                         &&
+                                         (flags & (BTRFS_BLOCK_GROUP_RAID1 |
+                                                   BTRFS_BLOCK_GROUP_RAID10)))
+                                        num_tolerated_disk_barrier_failures = 1;
+                        }
+                }
+                up_read(&sinfo->groups_sem);
+        }
+
+        return num_tolerated_disk_barrier_failures;
+}
+
 int write_all_supers(struct btrfs_root *root, int max_mirrors)
 {
         struct list_head *head;
@@ -2990,8 +3065,16 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors)
         mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
         head = &root->fs_info->fs_devices->devices;
 
-        if (do_barriers)
-                barrier_all_devices(root->fs_info);
+        if (do_barriers) {
+                ret = barrier_all_devices(root->fs_info);
+                if (ret) {
+                        mutex_unlock(
+                                &root->fs_info->fs_devices->device_list_mutex);
+                        btrfs_error(root->fs_info, ret,
+                                    "errors while submitting device barriers.");
+                        return ret;
+                }
+        }
 
         list_for_each_entry_rcu(dev, head, dev_list) {
                 if (!dev->bdev) {