dm raid: add raid4/5/6 journal write-back support via journal_mode option

Commit 63c32ed4afc ("dm raid: add raid4/5/6 journaling support") added
journal support to close the raid4/5/6 "write hole" -- in terms of
writethrough caching.

Introduce a "journal_mode" feature and use the new
r5c_journal_mode_set() API to add support for switching the journal
device's cache mode between write-through (the current default) and
write-back.

NOTE: If the journal device is not layered on resilent storage and it
fails, write-through mode will cause the "write hole" to reoccur.  But
if the journal fails while in write-back mode it will cause data loss
for any dirty cache entries unless resilent storage is used for the
journal.

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

2 files changed, 101 insertions, 14 deletions

diff --git a/Documentation/device-mapper/dm-raid.txt b/Documentation/device-mapper/dm-raid.txt
index 95c4c8dd6dd1..7e06e65586d4 100644
--- a/Documentation/device-mapper/dm-raid.txt
+++ b/Documentation/device-mapper/dm-raid.txt
@@ -170,6 +170,13 @@ The target is named "raid" and it accepts the following parameters:
                 Takeover/reshape is not possible with a raid4/5/6 journal device;
                 it has to be deconfigured before requesting these.
 
+        [journal_mode <mode>]
+                This option sets the caching mode on journaled raid4/5/6 raid sets
+                (see 'journal_dev <dev>' above) to 'writethrough' or 'writeback'.
+                If 'writeback' is selected the journal device has to be resilient
+                and must not suffer from the 'write hole' problem itself (e.g. use
+                raid1 or raid10) to avoid a single point of failure.
+
 <#raid_devs>: The number of devices composing the array.
         Each device consists of two entries.  The first is the device
         containing the metadata (if any); the second is the one containing the
@@ -254,7 +261,8 @@ recovery.  Here is a fuller description of the individual fields:
         <data_offset>   The current data offset to the start of the user data on
                         each component device of a raid set (see the respective
                         raid parameter to support out-of-place reshaping).
-        <journal_char>  'A' - active raid4/5/6 journal device.
+        <journal_char>  'A' - active write-through journal device.
+                        'a' - active write-back journal device.
                         'D' - dead journal device.
                         '-' - no journal device.
 
@@ -334,3 +342,4 @@ Version History
 1.10.1  Fix data corruption on reshape request
 1.11.0  Fix table line argument order
         (wrong raid10_copies/raid10_format sequence)
+1.11.1  Add raid4/5/6 journal write-back support via journal_mode option
diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index e07185fca638..0f61bb659b73 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2010-2011 Neil Brown
- * Copyright (C) 2010-2016 Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2010-2017 Red Hat, Inc. All rights reserved.
  *
  * This file is released under the GPL.
  */
@@ -79,7 +79,10 @@ struct raid_dev {
 #define __CTR_FLAG_RAID10_USE_NEAR_SETS 14 /* 2 */ /* Only with raid10! */
 
 /* New for v1.10.0 */
-#define __CTR_FLAG_JOURNAL_DEV          15 /* 2 */ /* Only with raid4/5/6! */
+#define __CTR_FLAG_JOURNAL_DEV          15 /* 2 */ /* Only with raid4/5/6 (journal device)! */
+
+/* New for v1.11.1 */
+#define __CTR_FLAG_JOURNAL_MODE         16 /* 2 */ /* Only with raid4/5/6 (journal mode)! */
 
 /*
  * Flags for rs->ctr_flags field.
@@ -100,6 +103,7 @@ struct raid_dev {
 #define CTR_FLAG_DATA_OFFSET            (1 << __CTR_FLAG_DATA_OFFSET)
 #define CTR_FLAG_RAID10_USE_NEAR_SETS   (1 << __CTR_FLAG_RAID10_USE_NEAR_SETS)
 #define CTR_FLAG_JOURNAL_DEV            (1 << __CTR_FLAG_JOURNAL_DEV)
+#define CTR_FLAG_JOURNAL_MODE           (1 << __CTR_FLAG_JOURNAL_MODE)
 
 #define RESUME_STAY_FROZEN_FLAGS (CTR_FLAG_DELTA_DISKS | CTR_FLAG_DATA_OFFSET)
 
@@ -175,7 +179,8 @@ struct raid_dev {
                                  CTR_FLAG_REGION_SIZE | \
                                  CTR_FLAG_DELTA_DISKS | \
                                  CTR_FLAG_DATA_OFFSET | \
-                                 CTR_FLAG_JOURNAL_DEV)
+                                 CTR_FLAG_JOURNAL_DEV | \
+                                 CTR_FLAG_JOURNAL_MODE)
 
 #define RAID6_VALID_FLAGS       (CTR_FLAG_SYNC | \
                                  CTR_FLAG_REBUILD | \
@@ -186,7 +191,8 @@ struct raid_dev {
                                  CTR_FLAG_REGION_SIZE | \
                                  CTR_FLAG_DELTA_DISKS | \
                                  CTR_FLAG_DATA_OFFSET | \
-                                 CTR_FLAG_JOURNAL_DEV)
+                                 CTR_FLAG_JOURNAL_DEV | \
+                                 CTR_FLAG_JOURNAL_MODE)
 /* ...valid options definitions per raid level */
 
 /*
@@ -239,6 +245,7 @@ struct raid_set {
         struct journal_dev {
                 struct dm_dev *dev;
                 struct md_rdev rdev;
+                int mode;
         } journal_dev;
 
         struct raid_dev dev[0];
@@ -326,6 +333,7 @@ static struct arg_name_flag {
         { CTR_FLAG_DELTA_DISKS, "delta_disks"},
         { CTR_FLAG_RAID10_USE_NEAR_SETS, "raid10_use_near_sets"},
         { CTR_FLAG_JOURNAL_DEV, "journal_dev" },
+        { CTR_FLAG_JOURNAL_MODE, "journal_mode" },
 };
 
 /* Return argument name string for given @flag */
@@ -344,6 +352,39 @@ static const char *dm_raid_arg_name_by_flag(const uint32_t flag)
         return NULL;
 }
 
+/* Define correlation of raid456 journal cache modes and dm-raid target line parameters */
+static struct {
+        const int mode;
+        const char *param;
+} _raid456_journal_mode[] = {
+        { R5C_JOURNAL_MODE_WRITE_THROUGH , "writethrough" },
+        { R5C_JOURNAL_MODE_WRITE_BACK    , "writeback" }
+};
+
+/* Return MD raid4/5/6 journal mode for dm @journal_mode one */
+static int dm_raid_journal_mode_to_md(const char *mode)
+{
+        int m = ARRAY_SIZE(_raid456_journal_mode);
+
+        while (m--)
+                if (!strcasecmp(mode, _raid456_journal_mode[m].param))
+                        return _raid456_journal_mode[m].mode;
+
+        return -EINVAL;
+}
+
+/* Return dm-raid raid4/5/6 journal mode string for @mode */
+static const char *md_journal_mode_to_dm_raid(const int mode)
+{
+        int m = ARRAY_SIZE(_raid456_journal_mode);
+
+        while (m--)
+                if (mode == _raid456_journal_mode[m].mode)
+                        return _raid456_journal_mode[m].param;
+
+        return "unknown";
+}
+
 /*
  * Bool helpers to test for various raid levels of a raid set.
  * It's level as reported by the superblock rather than
@@ -1183,7 +1224,7 @@ static int parse_raid_params(struct raid_set *rs, struct dm_arg_set *as,
                         continue;
                 }
 
-                /* "journal_dev dev" */
+                /* "journal_dev <dev>" */
                 if (!strcasecmp(key, dm_raid_arg_name_by_flag(CTR_FLAG_JOURNAL_DEV))) {
                         int r;
                         struct md_rdev *jdev;
@@ -1211,10 +1252,32 @@ static int parse_raid_params(struct raid_set *rs, struct dm_arg_set *as,
                                 rs->ti->error = "No space for raid4/5/6 journal";
                                 return -ENOSPC;
                         }
+                        rs->journal_dev.mode = R5C_JOURNAL_MODE_WRITE_THROUGH;
                         set_bit(Journal, &jdev->flags);
                         continue;
                 }
 
+                /* "journal_mode <mode>" ("journal_dev" mandatory!) */
+                if (!strcasecmp(key, dm_raid_arg_name_by_flag(CTR_FLAG_JOURNAL_MODE))) {
+                        int r;
+
+                        if (!test_bit(__CTR_FLAG_JOURNAL_DEV, &rs->ctr_flags)) {
+                                rs->ti->error = "raid4/5/6 'journal_mode' is invalid without 'journal_dev'";
+                                return -EINVAL;
+                        }
+                        if (test_and_set_bit(__CTR_FLAG_JOURNAL_MODE, &rs->ctr_flags)) {
+                                rs->ti->error = "Only one raid4/5/6 'journal_mode' argument allowed";
+                                return -EINVAL;
+                        }
+                        r = dm_raid_journal_mode_to_md(arg);
+                        if (r < 0) {
+                                rs->ti->error = "Invalid 'journal_mode' argument";
+                                return r;
+                        }
+                        rs->journal_dev.mode = r;
+                        continue;
+                }
+
                 /*
                  * Parameters with number values from here on.
                  */
@@ -3076,6 +3139,16 @@ static int raid_ctr(struct dm_target *ti, unsigned int argc, char **argv)
         rs->callbacks.congested_fn = raid_is_congested;
         dm_table_add_target_callbacks(ti->table, &rs->callbacks);
 
+        /* If raid4/5/6 journal mode explictely requested (only possible with journal dev) -> set it */
+        if (test_bit(__CTR_FLAG_JOURNAL_MODE, &rs->ctr_flags)) {
+                r = r5c_journal_mode_set(&rs->md, rs->journal_dev.mode);
+                if (r) {
+                        ti->error = "Failed to set raid4/5/6 journal mode";
+                        mddev_unlock(&rs->md);
+                        goto bad_journal_mode_set;
+                }
+        }
+
         mddev_suspend(&rs->md);
 
         /* Try to adjust the raid4/5/6 stripe cache size to the stripe size */
@@ -3109,6 +3182,7 @@ static int raid_ctr(struct dm_target *ti, unsigned int argc, char **argv)
         mddev_unlock(&rs->md);
         return 0;
 
+bad_journal_mode_set:
 bad_stripe_cache:
 bad_check_reshape:
         md_stop(&rs->md);
@@ -3180,18 +3254,18 @@ static const char *decipher_sync_action(struct mddev *mddev)
  * Status characters:
  *
  *  'D' = Dead/Failed raid set component or raid4/5/6 journal device
- *  'a' = Alive but not in-sync
- *  'A' = Alive and in-sync raid set component or alive raid4/5/6 journal device
+ *  'a' = Alive but not in-sync raid set component _or_ alive raid4/5/6 'write_back' journal device
+ *  'A' = Alive and in-sync raid set component _or_ alive raid4/5/6 'write_through' journal device
  *  '-' = Non-existing device (i.e. uspace passed '- -' into the ctr)
  */
-static const char *__raid_dev_status(struct md_rdev *rdev, bool array_in_sync)
+static const char *__raid_dev_status(struct raid_set *rs, struct md_rdev *rdev, bool array_in_sync)
 {
         if (!rdev->bdev)
                 return "-";
         else if (test_bit(Faulty, &rdev->flags))
                 return "D";
         else if (test_bit(Journal, &rdev->flags))
-                return "A";
+                return (rs->journal_dev.mode == R5C_JOURNAL_MODE_WRITE_THROUGH) ? "A" : "a";
         else if (!array_in_sync || !test_bit(In_sync, &rdev->flags))
                 return "a";
         else
@@ -3315,7 +3389,7 @@ static void raid_status(struct dm_target *ti, status_type_t type,
 
                 /* HM FIXME: do we want another state char for raid0? It shows 'D'/'A'/'-' now */
                 for (i = 0; i < rs->raid_disks; i++)
-                        DMEMIT(__raid_dev_status(&rs->dev[i].rdev, array_in_sync));
+                        DMEMIT(__raid_dev_status(rs, &rs->dev[i].rdev, array_in_sync));
 
                 /*
                  * In-sync/Reshape ratio:
@@ -3366,7 +3440,7 @@ static void raid_status(struct dm_target *ti, status_type_t type,
                  * v1.10.0+:
                  */
                 DMEMIT(" %s", test_bit(__CTR_FLAG_JOURNAL_DEV, &rs->ctr_flags) ?
-                              __raid_dev_status(&rs->journal_dev.rdev, 0) : "-");
+                              __raid_dev_status(rs, &rs->journal_dev.rdev, 0) : "-");
                 break;
 
         case STATUSTYPE_TABLE:
@@ -3381,7 +3455,8 @@ static void raid_status(struct dm_target *ti, status_type_t type,
                                   write_mostly_params +
                                   hweight32(rs->ctr_flags & CTR_FLAG_OPTIONS_NO_ARGS) +
                                   hweight32(rs->ctr_flags & CTR_FLAG_OPTIONS_ONE_ARG) * 2 +
-                                  (test_bit(__CTR_FLAG_JOURNAL_DEV, &rs->ctr_flags) ? 2 : 0);
+                                  (test_bit(__CTR_FLAG_JOURNAL_DEV, &rs->ctr_flags) ? 2 : 0) +
+                                  (test_bit(__CTR_FLAG_JOURNAL_MODE, &rs->ctr_flags) ? 2 : 0);
 
                 /* Emit table line */
                 /* This has to be in the documented order for userspace! */
@@ -3433,6 +3508,9 @@ static void raid_status(struct dm_target *ti, status_type_t type,
                 if (test_bit(__CTR_FLAG_JOURNAL_DEV, &rs->ctr_flags))
                         DMEMIT(" %s %s", dm_raid_arg_name_by_flag(CTR_FLAG_JOURNAL_DEV),
                                         __get_dev_name(rs->journal_dev.dev));
+                if (test_bit(__CTR_FLAG_JOURNAL_MODE, &rs->ctr_flags))
+                        DMEMIT(" %s %s", dm_raid_arg_name_by_flag(CTR_FLAG_JOURNAL_MODE),
+                                         md_journal_mode_to_dm_raid(rs->journal_dev.mode));
                 DMEMIT(" %d", rs->raid_disks);
                 for (i = 0; i < rs->raid_disks; i++)
                         DMEMIT(" %s %s", __get_dev_name(rs->dev[i].meta_dev),
@@ -3793,7 +3871,7 @@ static void raid_resume(struct dm_target *ti)
 
 static struct target_type raid_target = {
         .name = "raid",
-        .version = {1, 11, 0},
+        .version = {1, 11, 1},
         .module = THIS_MODULE,
         .ctr = raid_ctr,
         .dtr = raid_dtr,