btrfs: add framework to handle device flush error as a volume

This adds comments to the flush error handling part of the code, and
hopes to maintain the same logic with a framework which can be used to
handle the errors at the volume level.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 53 insertions, 4 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 5f678dcb20e6..bafdd2fe8f88 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3509,6 +3509,10 @@ static int write_dev_flush(struct btrfs_device *device, int wait)
         if (wait) {
                 bio = device->flush_bio;
                 if (!bio)
+                        /*
+                         * This means the alloc has failed with ENOMEM, however
+                         * here we return 0, as its not a device error.
+                         */
                         return 0;
 
                 wait_for_completion(&device->flush_wait);
@@ -3548,6 +3552,32 @@ static int write_dev_flush(struct btrfs_device *device, int wait)
         return 0;
 }
 
+static int check_barrier_error(struct btrfs_fs_devices *fsdevs)
+{
+        int submit_flush_error = 0;
+        int dev_flush_error = 0;
+        struct btrfs_device *dev;
+        int tolerance;
+
+        list_for_each_entry_rcu(dev, &fsdevs->devices, dev_list) {
+                if (!dev->bdev) {
+                        submit_flush_error++;
+                        dev_flush_error++;
+                        continue;
+                }
+                if (dev->last_flush_error == -ENOMEM)
+                        submit_flush_error++;
+                if (dev->last_flush_error && dev->last_flush_error != -ENOMEM)
+                        dev_flush_error++;
+        }
+
+        tolerance = fsdevs->fs_info->num_tolerated_disk_barrier_failures;
+        if (submit_flush_error > tolerance || dev_flush_error > tolerance)
+                return -EIO;
+
+        return 0;
+}
+
 /*
  * send an empty flush down to each device in parallel,
  * then wait for them
@@ -3575,6 +3605,7 @@ static int barrier_all_devices(struct btrfs_fs_info *info)
                 ret = write_dev_flush(dev, 0);
                 if (ret)
                         errors_send++;
+                dev->last_flush_error = ret;
         }
 
         /* wait for all the barriers */
@@ -3589,12 +3620,30 @@ static int barrier_all_devices(struct btrfs_fs_info *info)
                         continue;
 
                 ret = write_dev_flush(dev, 1);
-                if (ret)
+                if (ret) {
+                        dev->last_flush_error = ret;
                         errors_wait++;
+                }
+        }
+
+        /*
+         * Try hard in case of flush. Lets say, in RAID1 we have
+         * the following situation
+         *  dev1: EIO dev2: ENOMEM
+         * this is not a fatal error as we hope to recover from
+         * ENOMEM in the next attempt to flush.
+         * But the following is considered as fatal
+         *  dev1: ENOMEM dev2: ENOMEM
+         *  dev1: bdev == NULL dev2: ENOMEM
+         */
+        if (errors_send || errors_wait) {
+                /*
+                 * At some point we need the status of all disks
+                 * to arrive at the volume status. So error checking
+                 * is being pushed to a separate loop.
+                 */
+                return check_barrier_error(info->fs_devices);
         }
-        if (errors_send > info->num_tolerated_disk_barrier_failures ||
-            errors_wait > info->num_tolerated_disk_barrier_failures)
-                return -EIO;
         return 0;
 }