[PATCH] md: fix raid6 resync check/repair code

raid6 currently does not check the P/Q syndromes when doing a resync, it just
calculates the correct value and writes it.  Doing the check can reduce writes
(often to 0) for a resync, and it is needed to properly implement the

  echo check > sync_action

operation.

This patch implements the appropriate checks and tidies up some related code.

It also allows raid6 user-requested resync to bypass the intent bitmap.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 108 insertions, 76 deletions

diff --git a/drivers/md/raid6main.c b/drivers/md/raid6main.c
index 304455d236f9..52e8796bb8ac 100644
--- a/drivers/md/raid6main.c
+++ b/drivers/md/raid6main.c
@@ -805,7 +805,7 @@ static void compute_parity(struct stripe_head *sh, int method)
 }
 
 /* Compute one missing block */
-static void compute_block_1(struct stripe_head *sh, int dd_idx)
+static void compute_block_1(struct stripe_head *sh, int dd_idx, int nozero)
 {
         raid6_conf_t *conf = sh->raid_conf;
         int i, count, disks = conf->raid_disks;
@@ -821,7 +821,7 @@ static void compute_block_1(struct stripe_head *sh, int dd_idx)
                 compute_parity(sh, UPDATE_PARITY);
         } else {
                 ptr[0] = page_address(sh->dev[dd_idx].page);
-                memset(ptr[0], 0, STRIPE_SIZE);
+                if (!nozero) memset(ptr[0], 0, STRIPE_SIZE);
                 count = 1;
                 for (i = disks ; i--; ) {
                         if (i == dd_idx || i == qd_idx)
@@ -838,7 +838,8 @@ static void compute_block_1(struct stripe_head *sh, int dd_idx)
                 }
                 if (count != 1)
                         xor_block(count, STRIPE_SIZE, ptr);
-                set_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
+                if (!nozero) set_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
+                else clear_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
         }
 }
 
@@ -871,7 +872,7 @@ static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
                         return;
                 } else {
                         /* We're missing D+Q; recompute D from P */
-                        compute_block_1(sh, (dd_idx1 == qd_idx) ? dd_idx2 : dd_idx1);
+                        compute_block_1(sh, (dd_idx1 == qd_idx) ? dd_idx2 : dd_idx1, 0);
                         compute_parity(sh, UPDATE_PARITY); /* Is this necessary? */
                         return;
                 }
@@ -982,6 +983,12 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
 }
 
 
+static int page_is_zero(struct page *p)
+{
+        char *a = page_address(p);
+        return ((*(u32*)a) == 0 &&
+                memcmp(a, a+4, STRIPE_SIZE-4)==0);
+}
 /*
  * handle_stripe - do things to a stripe.
  *
@@ -1000,7 +1007,7 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
  *
  */
 
-static void handle_stripe(struct stripe_head *sh)
+static void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
 {
         raid6_conf_t *conf = sh->raid_conf;
         int disks = conf->raid_disks;
@@ -1228,7 +1235,7 @@ static void handle_stripe(struct stripe_head *sh)
                                 if (uptodate == disks-1) {
                                         PRINTK("Computing stripe %llu block %d\n",
                                                (unsigned long long)sh->sector, i);
-                                        compute_block_1(sh, i);
+                                        compute_block_1(sh, i, 0);
                                         uptodate++;
                                 } else if ( uptodate == disks-2 && failed >= 2 ) {
                                         /* Computing 2-failure is *very* expensive; only do it if failed >= 2 */
@@ -1323,7 +1330,7 @@ static void handle_stripe(struct stripe_head *sh)
                                 /* We have failed blocks and need to compute them */
                                 switch ( failed ) {
                                 case 0: BUG();
-                                case 1: compute_block_1(sh, failed_num[0]); break;
+                                case 1: compute_block_1(sh, failed_num[0], 0); break;
                                 case 2: compute_block_2(sh, failed_num[0], failed_num[1]); break;
                                 default: BUG(); /* This request should have been failed? */
                                 }
@@ -1338,12 +1345,10 @@ static void handle_stripe(struct stripe_head *sh)
                                                (unsigned long long)sh->sector, i);
                                         locked++;
                                         set_bit(R5_Wantwrite, &sh->dev[i].flags);
-#if 0 /**** FIX: I don't understand the logic here... ****/
-                                        if (!test_bit(R5_Insync, &sh->dev[i].flags)
-                                            || ((i==pd_idx || i==qd_idx) && failed == 0)) /* FIX? */
-                                                set_bit(STRIPE_INSYNC, &sh->state);
-#endif
                                 }
+                        /* after a RECONSTRUCT_WRITE, the stripe MUST be in-sync */
+                        set_bit(STRIPE_INSYNC, &sh->state);
+
                         if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                 atomic_dec(&conf->preread_active_stripes);
                                 if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
@@ -1356,79 +1361,97 @@ static void handle_stripe(struct stripe_head *sh)
          * Any reads will already have been scheduled, so we just see if enough data
          * is available
          */
-        if (syncing && locked == 0 &&
-            !test_bit(STRIPE_INSYNC, &sh->state) && failed <= 2) {
-                set_bit(STRIPE_HANDLE, &sh->state);
-#if 0 /* RAID-6: Don't support CHECK PARITY yet */
-                if (failed == 0) {
-                        char *pagea;
-                        if (uptodate != disks)
-                                BUG();
-                        compute_parity(sh, CHECK_PARITY);
-                        uptodate--;
-                        pagea = page_address(sh->dev[pd_idx].page);
-                        if ((*(u32*)pagea) == 0 &&
-                            !memcmp(pagea, pagea+4, STRIPE_SIZE-4)) {
-                                /* parity is correct (on disc, not in buffer any more) */
-                                set_bit(STRIPE_INSYNC, &sh->state);
-                        }
-                }
-#endif
-                if (!test_bit(STRIPE_INSYNC, &sh->state)) {
-                        int failed_needupdate[2];
-                        struct r5dev *adev, *bdev;
-
-                        if ( failed < 1 )
-                                failed_num[0] = pd_idx;
-                        if ( failed < 2 )
-                                failed_num[1] = (failed_num[0] == qd_idx) ? pd_idx : qd_idx;
+        if (syncing && locked == 0 && !test_bit(STRIPE_INSYNC, &sh->state)) {
+                int update_p = 0, update_q = 0;
+                struct r5dev *dev;
 
-                        failed_needupdate[0] = !test_bit(R5_UPTODATE, &sh->dev[failed_num[0]].flags);
-                        failed_needupdate[1] = !test_bit(R5_UPTODATE, &sh->dev[failed_num[1]].flags);
+                set_bit(STRIPE_HANDLE, &sh->state);
 
-                        PRINTK("sync: failed=%d num=%d,%d fnu=%u%u\n",
-                               failed, failed_num[0], failed_num[1], failed_needupdate[0], failed_needupdate[1]);
+                BUG_ON(failed>2);
+                BUG_ON(uptodate < disks);
+                /* Want to check and possibly repair P and Q.
+                 * However there could be one 'failed' device, in which
+                 * case we can only check one of them, possibly using the
+                 * other to generate missing data
+                 */
 
-#if 0  /* RAID-6: This code seems to require that CHECK_PARITY destroys the uptodateness of the parity */
-                        /* should be able to compute the missing block(s) and write to spare */
-                        if ( failed_needupdate[0] ^ failed_needupdate[1] ) {
-                                if (uptodate+1 != disks)
-                                        BUG();
-                                compute_block_1(sh, failed_needupdate[0] ? failed_num[0] : failed_num[1]);
-                                uptodate++;
-                        } else if ( failed_needupdate[0] & failed_needupdate[1] ) {
-                                if (uptodate+2 != disks)
-                                        BUG();
-                                compute_block_2(sh, failed_num[0], failed_num[1]);
-                                uptodate += 2;
+                /* If !tmp_page, we cannot do the calculations,
+                 * but as we have set STRIPE_HANDLE, we will soon be called
+                 * by stripe_handle with a tmp_page - just wait until then.
+                 */
+                if (tmp_page) {
+                        if (failed == q_failed) {
+                                /* The only possible failed device holds 'Q', so it makes
+                                 * sense to check P (If anything else were failed, we would
+                                 * have used P to recreate it).
+                                 */
+                                compute_block_1(sh, pd_idx, 1);
+                                if (!page_is_zero(sh->dev[pd_idx].page)) {
+                                        compute_block_1(sh,pd_idx,0);
+                                        update_p = 1;
+                                }
+                        }
+                        if (!q_failed && failed < 2) {
+                                /* q is not failed, and we didn't use it to generate
+                                 * anything, so it makes sense to check it
+                                 */
+                                memcpy(page_address(tmp_page),
+                                       page_address(sh->dev[qd_idx].page),
+                                       STRIPE_SIZE);
+                                compute_parity(sh, UPDATE_PARITY);
+                                if (memcmp(page_address(tmp_page),
+                                           page_address(sh->dev[qd_idx].page),
+                                           STRIPE_SIZE)!= 0) {
+                                        clear_bit(STRIPE_INSYNC, &sh->state);
+                                        update_q = 1;
+                                }
+                        }
+                        if (update_p || update_q) {
+                                conf->mddev->resync_mismatches += STRIPE_SECTORS;
+                                if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
+                                        /* don't try to repair!! */
+                                        update_p = update_q = 0;
                         }
-#else
-                        compute_block_2(sh, failed_num[0], failed_num[1]);
-                        uptodate += failed_needupdate[0] + failed_needupdate[1];
-#endif
 
-                        if (uptodate != disks)
-                                BUG();
+                        /* now write out any block on a failed drive,
+                         * or P or Q if they need it
+                         */
 
-                        PRINTK("Marking for sync stripe %llu blocks %d,%d\n",
-                               (unsigned long long)sh->sector, failed_num[0], failed_num[1]);
+                        if (failed == 2) {
+                                dev = &sh->dev[failed_num[1]];
+                                locked++;
+                                set_bit(R5_LOCKED, &dev->flags);
+                                set_bit(R5_Wantwrite, &dev->flags);
+                                set_bit(R5_Syncio, &dev->flags);
+                        }
+                        if (failed >= 1) {
+                                dev = &sh->dev[failed_num[0]];
+                                locked++;
+                                set_bit(R5_LOCKED, &dev->flags);
+                                set_bit(R5_Wantwrite, &dev->flags);
+                                set_bit(R5_Syncio, &dev->flags);
+                        }
 
-                        /**** FIX: Should we really do both of these unconditionally? ****/
-                        adev = &sh->dev[failed_num[0]];
-                        locked += !test_bit(R5_LOCKED, &adev->flags);
-                        set_bit(R5_LOCKED, &adev->flags);
-                        set_bit(R5_Wantwrite, &adev->flags);
-                        bdev = &sh->dev[failed_num[1]];
-                        locked += !test_bit(R5_LOCKED, &bdev->flags);
-                        set_bit(R5_LOCKED, &bdev->flags);
+                        if (update_p) {
+                                dev = &sh->dev[pd_idx];
+                                locked ++;
+                                set_bit(R5_LOCKED, &dev->flags);
+                                set_bit(R5_Wantwrite, &dev->flags);
+                                set_bit(R5_Syncio, &dev->flags);
+                        }
+                        if (update_q) {
+                                dev = &sh->dev[qd_idx];
+                                locked++;
+                                set_bit(R5_LOCKED, &dev->flags);
+                                set_bit(R5_Wantwrite, &dev->flags);
+                                set_bit(R5_Syncio, &dev->flags);
+                        }
                         clear_bit(STRIPE_DEGRADED, &sh->state);
-                        set_bit(R5_Wantwrite, &bdev->flags);
 
                         set_bit(STRIPE_INSYNC, &sh->state);
-                        set_bit(R5_Syncio, &adev->flags);
-                        set_bit(R5_Syncio, &bdev->flags);
                 }
         }
+
         if (syncing && locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
                 md_done_sync(conf->mddev, STRIPE_SECTORS,1);
                 clear_bit(STRIPE_SYNCING, &sh->state);
@@ -1664,7 +1687,7 @@ static int make_request (request_queue_t *q, struct bio * bi)
                         }
                         finish_wait(&conf->wait_for_overlap, &w);
                         raid6_plug_device(conf);
-                        handle_stripe(sh);
+                        handle_stripe(sh, NULL);
                         release_stripe(sh);
                 } else {
                         /* cannot get stripe for read-ahead, just give-up */
@@ -1728,6 +1751,7 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
                 return rv;
         }
         if (!bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) &&
+            !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
             !conf->fullsync && sync_blocks >= STRIPE_SECTORS) {
                 /* we can skip this block, and probably more */
                 sync_blocks /= STRIPE_SECTORS;
@@ -1765,7 +1789,7 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
         clear_bit(STRIPE_INSYNC, &sh->state);
         spin_unlock(&sh->lock);
 
-        handle_stripe(sh);
+        handle_stripe(sh, NULL);
         release_stripe(sh);
 
         return STRIPE_SECTORS;
@@ -1821,7 +1845,7 @@ static void raid6d (mddev_t *mddev)
                 spin_unlock_irq(&conf->device_lock);
 
                 handled++;
-                handle_stripe(sh);
+                handle_stripe(sh, conf->spare_page);
                 release_stripe(sh);
 
                 spin_lock_irq(&conf->device_lock);
@@ -1860,6 +1884,10 @@ static int run(mddev_t *mddev)
                 goto abort;
         memset(conf->stripe_hashtbl, 0, HASH_PAGES * PAGE_SIZE);
 
+        conf->spare_page = alloc_page(GFP_KERNEL);
+        if (!conf->spare_page)
+                goto abort;
+
         spin_lock_init(&conf->device_lock);
         init_waitqueue_head(&conf->wait_for_stripe);
         init_waitqueue_head(&conf->wait_for_overlap);
@@ -1996,6 +2024,8 @@ static int run(mddev_t *mddev)
 abort:
         if (conf) {
                 print_raid6_conf(conf);
+                if (conf->spare_page)
+                        page_cache_release(conf->spare_page);
                 if (conf->stripe_hashtbl)
                         free_pages((unsigned long) conf->stripe_hashtbl,
                                                         HASH_PAGES_ORDER);
diff --git a/include/linux/raid/raid5.h b/include/linux/raid/raid5.h
index f025ba6fb14c..e9c1c0d4f90b 100644
--- a/include/linux/raid/raid5.h
+++ b/include/linux/raid/raid5.h
@@ -228,6 +228,8 @@ struct raid5_private_data {
                                             * Cleared when a sync completes.
                                             */
 
+        struct page             *spare_page; /* Used when checking P/Q in raid6 */
+
         /*
          * Free stripes pool
          */