UBI: improve corrupted flash handling

This patch improves the way UBI handles corrupted flash, or flash
containing garbage or non-UBI data, which is the same from UBI POW.
Namely, we do the following:

* if 5% or more PEBs are corrupted, refuse the flash
* if less than 5% PEBs are corrupted, do not refuse the flash
  and format these PEBs
* if less than 8 PEBs are corrupted, format them silently, otherwise
  print a warning message.

Reported-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Tested-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>

1 files changed, 82 insertions, 19 deletions

diff --git a/drivers/mtd/ubi/scan.c b/drivers/mtd/ubi/scan.c
index a20f278d0c6c..6b7c0c4baf07 100644
--- a/drivers/mtd/ubi/scan.c
+++ b/drivers/mtd/ubi/scan.c
@@ -760,8 +760,6 @@ static int process_eb(struct ubi_device *ubi, struct ubi_scan_info *si,
                 bitflips = 1;
         }
 
-        si->is_empty = 0;
-
         if (!ec_corr) {
                 int image_seq;
 
@@ -892,6 +890,85 @@ adjust_mean_ec:
 }
 
 /**
+ * check_what_we_have - check what PEB were found by scanning.
+ * @ubi: UBI device description object
+ * @si: scanning information
+ *
+ * This is a helper function which takes a look what PEBs were found by
+ * scanning, and decides whether the flash is empty and should be formatted and
+ * whether there are too many corrupted PEBs and we should not attach this
+ * MTD device. Returns zero if we should proceed with attaching the MTD device,
+ * and %-EINVAL if we should not.
+ */
+static int check_what_we_have(const struct ubi_device *ubi,
+                              struct ubi_scan_info *si)
+{
+        struct ubi_scan_leb *seb;
+        int max_corr;
+
+        max_corr = ubi->peb_count - si->bad_peb_count - si->alien_peb_count;
+        max_corr = max_corr / 20 ?: 8;
+
+        /*
+         * Few corrupted PEBs are not a problem and may be just a result of
+         * unclean reboots. However, many of them may indicate some problems
+         * with the flash HW or driver.
+         */
+        if (si->corr_peb_count >= 8) {
+                ubi_warn("%d PEBs are corrupted", si->corr_peb_count);
+                printk(KERN_WARNING "corrupted PEBs are:");
+                list_for_each_entry(seb, &si->corr, u.list)
+                        printk(KERN_CONT " %d", seb->pnum);
+                printk(KERN_CONT "\n");
+
+                /*
+                 * If too many PEBs are corrupted, we refuse attaching,
+                 * otherwise, only print a warning.
+                 */
+                if (si->corr_peb_count >= max_corr) {
+                        ubi_err("too many corrupted PEBs, refusing this device");
+                        return -EINVAL;
+                }
+        }
+
+        if (si->free_peb_count + si->used_peb_count +
+            si->alien_peb_count == 0) {
+                /* No UBI-formatted eraseblocks were found */
+                if (si->corr_peb_count == si->read_err_count &&
+                    si->corr_peb_count < 8) {
+                        /* No or just few corrupted PEBs, and all of them had a
+                         * read error. We assume that those are bad PEBs, which
+                         * were just not marked as bad so far.
+                         *
+                         * This piece of code basically tries to distinguish
+                         * between the following 2 situations:
+                         *
+                         * 1. Flash is empty, but there are few bad PEBs, which
+                         *    are not marked as bad so far, and which were read
+                         *    with error. We want to go ahead and format this
+                         *    flash. While formating, the faulty PEBs will
+                         *    probably be marked as bad.
+                         *
+                         * 2. Flash probably contains non-UBI data and we do
+                         * not want to format it and destroy possibly needed
+                         * data (e.g., consider the case when the bootloader
+                         * MTD partition was accidentally fed to UBI).
+                         */
+                        si->is_empty = 1;
+                        ubi_msg("empty MTD device detected");
+                } else {
+                        ubi_err("MTD device possibly contains non-UBI data, "
+                                "refusing it");
+                        return -EINVAL;
+                }
+        }
+
+        if (si->corr_peb_count >= 0)
+                ubi_msg("corrupted PEBs will be formatted");
+        return 0;
+}
+
+/**
  * ubi_scan - scan an MTD device.
  * @ubi: UBI device description object
  *
@@ -915,7 +992,6 @@ struct ubi_scan_info *ubi_scan(struct ubi_device *ubi)
         INIT_LIST_HEAD(&si->erase);
         INIT_LIST_HEAD(&si->alien);
         si->volumes = RB_ROOT;
-        si->is_empty = 1;
 
         err = -ENOMEM;
         ech = kzalloc(ubi->ec_hdr_alsize, GFP_KERNEL);
@@ -941,22 +1017,9 @@ struct ubi_scan_info *ubi_scan(struct ubi_device *ubi)
         if (si->ec_count)
                 si->mean_ec = div_u64(si->ec_sum, si->ec_count);
 
-        if (si->is_empty)
-                ubi_msg("empty MTD device detected");
-
-        /*
-         * Few corrupted PEBs are not a problem and may be just a result of
-         * unclean reboots. However, many of them may indicate some problems
-         * with the flash HW or driver. Print a warning in this case.
-         */
-        if (si->corr_peb_count >= 8 ||
-            si->corr_peb_count >= ubi->peb_count / 4) {
-                ubi_warn("%d PEBs are corrupted", si->corr_peb_count);
-                printk(KERN_WARNING "corrupted PEBs are:");
-                list_for_each_entry(seb, &si->corr, u.list)
-                        printk(KERN_CONT " %d", seb->pnum);
-                printk(KERN_CONT "\n");
-        }
+        err = check_what_we_have(ubi, si);
+        if (err)
+                goto out_vidh;
 
         /*
          * In case of unknown erase counter we use the mean erase counter