Merge branch 'mpi-master' into wip-k-fmlpwip-k-fmlp

Conflicts:
	litmus/sched_cedf.c

1 files changed, 317 insertions, 133 deletions

diff --git a/drivers/mtd/ubi/scan.c b/drivers/mtd/ubi/scan.c
index 69b52e9c9489..2135a53732ff 100644
--- a/drivers/mtd/ubi/scan.c
+++ b/drivers/mtd/ubi/scan.c
@@ -29,7 +29,7 @@
  * objects which are kept in volume RB-tree with root at the @volumes field.
  * The RB-tree is indexed by the volume ID.
  *
- * Found logical eraseblocks are represented by &struct ubi_scan_leb objects.
+ * Scanned logical eraseblocks are represented by &struct ubi_scan_leb objects.
  * These objects are kept in per-volume RB-trees with the root at the
  * corresponding &struct ubi_scan_volume object. To put it differently, we keep
  * an RB-tree of per-volume objects and each of these objects is the root of
@@ -38,6 +38,47 @@
  * Corrupted physical eraseblocks are put to the @corr list, free physical
  * eraseblocks are put to the @free list and the physical eraseblock to be
  * erased are put to the @erase list.
+ *
+ * About corruptions
+ * ~~~~~~~~~~~~~~~~~
+ *
+ * UBI protects EC and VID headers with CRC-32 checksums, so it can detect
+ * whether the headers are corrupted or not. Sometimes UBI also protects the
+ * data with CRC-32, e.g., when it executes the atomic LEB change operation, or
+ * when it moves the contents of a PEB for wear-leveling purposes.
+ *
+ * UBI tries to distinguish between 2 types of corruptions.
+ *
+ * 1. Corruptions caused by power cuts. These are expected corruptions and UBI
+ * tries to handle them gracefully, without printing too many warnings and
+ * error messages. The idea is that we do not lose important data in these case
+ * - we may lose only the data which was being written to the media just before
+ * the power cut happened, and the upper layers (e.g., UBIFS) are supposed to
+ * handle such data losses (e.g., by using the FS journal).
+ *
+ * When UBI detects a corruption (CRC-32 mismatch) in a PEB, and it looks like
+ * the reason is a power cut, UBI puts this PEB to the @erase list, and all
+ * PEBs in the @erase list are scheduled for erasure later.
+ *
+ * 2. Unexpected corruptions which are not caused by power cuts. During
+ * scanning, such PEBs are put to the @corr list and UBI preserves them.
+ * Obviously, this lessens the amount of available PEBs, and if at some  point
+ * UBI runs out of free PEBs, it switches to R/O mode. UBI also loudly informs
+ * about such PEBs every time the MTD device is attached.
+ *
+ * However, it is difficult to reliably distinguish between these types of
+ * corruptions and UBI's strategy is as follows. UBI assumes corruption type 2
+ * if the VID header is corrupted and the data area does not contain all 0xFFs,
+ * and there were no bit-flips or integrity errors while reading the data area.
+ * Otherwise UBI assumes corruption type 1. So the decision criteria are as
+ * follows.
+ *   o If the data area contains only 0xFFs, there is no data, and it is safe
+ *     to just erase this PEB - this is corruption type 1.
+ *   o If the data area has bit-flips or data integrity errors (ECC errors on
+ *     NAND), it is probably a PEB which was being erased when power cut
+ *     happened, so this is corruption type 1. However, this is just a guess,
+ *     which might be wrong.
+ *   o Otherwise this it corruption type 2.
  */
 
 #include <linux/err.h>
@@ -47,7 +88,7 @@
 #include <linux/random.h>
 #include "ubi.h"
 
-#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID
+#ifdef CONFIG_MTD_UBI_DEBUG
 static int paranoid_check_si(struct ubi_device *ubi, struct ubi_scan_info *si);
 #else
 #define paranoid_check_si(ubi, si) 0
@@ -62,39 +103,69 @@ static struct ubi_vid_hdr *vidh;
  * @si: scanning information
  * @pnum: physical eraseblock number to add
  * @ec: erase counter of the physical eraseblock
+ * @to_head: if not zero, add to the head of the list
  * @list: the list to add to
  *
- * This function adds physical eraseblock @pnum to free, erase, corrupted or
- * alien lists. Returns zero in case of success and a negative error code in
- * case of failure.
+ * This function adds physical eraseblock @pnum to free, erase, or alien lists.
+ * If @to_head is not zero, PEB will be added to the head of the list, which
+ * basically means it will be processed first later. E.g., we add corrupted
+ * PEBs (corrupted due to power cuts) to the head of the erase list to make
+ * sure we erase them first and get rid of corruptions ASAP. This function
+ * returns zero in case of success and a negative error code in case of
+ * failure.
  */
-static int add_to_list(struct ubi_scan_info *si, int pnum, int ec,
+static int add_to_list(struct ubi_scan_info *si, int pnum, int ec, int to_head,
                        struct list_head *list)
 {
         struct ubi_scan_leb *seb;
 
         if (list == &si->free) {
                 dbg_bld("add to free: PEB %d, EC %d", pnum, ec);
-                si->free_peb_count += 1;
         } else if (list == &si->erase) {
                 dbg_bld("add to erase: PEB %d, EC %d", pnum, ec);
-                si->erase_peb_count += 1;
-        } else if (list == &si->corr) {
-                dbg_bld("add to corrupted: PEB %d, EC %d", pnum, ec);
-                si->corr_peb_count += 1;
         } else if (list == &si->alien) {
                 dbg_bld("add to alien: PEB %d, EC %d", pnum, ec);
                 si->alien_peb_count += 1;
         } else
                 BUG();
 
-        seb = kmalloc(sizeof(struct ubi_scan_leb), GFP_KERNEL);
+        seb = kmem_cache_alloc(si->scan_leb_slab, GFP_KERNEL);
+        if (!seb)
+                return -ENOMEM;
+
+        seb->pnum = pnum;
+        seb->ec = ec;
+        if (to_head)
+                list_add(&seb->u.list, list);
+        else
+                list_add_tail(&seb->u.list, list);
+        return 0;
+}
+
+/**
+ * add_corrupted - add a corrupted physical eraseblock.
+ * @si: scanning information
+ * @pnum: physical eraseblock number to add
+ * @ec: erase counter of the physical eraseblock
+ *
+ * This function adds corrupted physical eraseblock @pnum to the 'corr' list.
+ * The corruption was presumably not caused by a power cut. Returns zero in
+ * case of success and a negative error code in case of failure.
+ */
+static int add_corrupted(struct ubi_scan_info *si, int pnum, int ec)
+{
+        struct ubi_scan_leb *seb;
+
+        dbg_bld("add to corrupted: PEB %d, EC %d", pnum, ec);
+
+        seb = kmem_cache_alloc(si->scan_leb_slab, GFP_KERNEL);
         if (!seb)
                 return -ENOMEM;
 
+        si->corr_peb_count += 1;
         seb->pnum = pnum;
         seb->ec = ec;
-        list_add_tail(&seb->u.list, list);
+        list_add(&seb->u.list, &si->corr);
         return 0;
 }
 
@@ -258,8 +329,8 @@ static int compare_lebs(struct ubi_device *ubi, const struct ubi_scan_leb *seb,
                  * created before sequence numbers support has been added. At
                  * that times we used 32-bit LEB versions stored in logical
                  * eraseblocks. That was before UBI got into mainline. We do not
-                 * support these images anymore. Well, those images will work
-                 * still work, but only if no unclean reboots happened.
+                 * support these images anymore. Well, those images still work,
+                 * but only if no unclean reboots happened.
                  */
                 ubi_err("unsupported on-flash UBI format\n");
                 return -EINVAL;
@@ -285,19 +356,25 @@ static int compare_lebs(struct ubi_device *ubi, const struct ubi_scan_leb *seb,
                         return 1;
                 }
         } else {
-                pnum = seb->pnum;
+                if (!seb->copy_flag) {
+                        /* It is not a copy, so it is newer */
+                        dbg_bld("first PEB %d is newer, copy_flag is unset",
+                                pnum);
+                        return bitflips << 1;
+                }
 
                 vh = ubi_zalloc_vid_hdr(ubi, GFP_KERNEL);
                 if (!vh)
                         return -ENOMEM;
 
+                pnum = seb->pnum;
                 err = ubi_io_read_vid_hdr(ubi, pnum, vh, 0);
                 if (err) {
                         if (err == UBI_IO_BITFLIPS)
                                 bitflips = 1;
                         else {
                                 dbg_err("VID of PEB %d header is bad, but it "
-                                        "was OK earlier", pnum);
+                                        "was OK earlier, err %d", pnum, err);
                                 if (err > 0)
                                         err = -EIO;
 
@@ -305,14 +382,6 @@ static int compare_lebs(struct ubi_device *ubi, const struct ubi_scan_leb *seb,
                         }
                 }
 
-                if (!vh->copy_flag) {
-                        /* It is not a copy, so it is newer */
-                        dbg_bld("first PEB %d is newer, copy_flag is unset",
-                                pnum);
-                        err = bitflips << 1;
-                        goto out_free_vidh;
-                }
-
                 vid_hdr = vh;
         }
 
@@ -463,18 +532,15 @@ int ubi_scan_add_used(struct ubi_device *ubi, struct ubi_scan_info *si,
                         if (err)
                                 return err;
 
-                        if (cmp_res & 4)
-                                err = add_to_list(si, seb->pnum, seb->ec,
-                                                  &si->corr);
-                        else
-                                err = add_to_list(si, seb->pnum, seb->ec,
-                                                  &si->erase);
+                        err = add_to_list(si, seb->pnum, seb->ec, cmp_res & 4,
+                                          &si->erase);
                         if (err)
                                 return err;
 
                         seb->ec = ec;
                         seb->pnum = pnum;
                         seb->scrub = ((cmp_res & 2) || bitflips);
+                        seb->copy_flag = vid_hdr->copy_flag;
                         seb->sqnum = sqnum;
 
                         if (sv->highest_lnum == lnum)
@@ -487,10 +553,8 @@ int ubi_scan_add_used(struct ubi_device *ubi, struct ubi_scan_info *si,
                          * This logical eraseblock is older than the one found
                          * previously.
                          */
-                        if (cmp_res & 4)
-                                return add_to_list(si, pnum, ec, &si->corr);
-                        else
-                                return add_to_list(si, pnum, ec, &si->erase);
+                        return add_to_list(si, pnum, ec, cmp_res & 4,
+                                           &si->erase);
                 }
         }
 
@@ -503,15 +567,16 @@ int ubi_scan_add_used(struct ubi_device *ubi, struct ubi_scan_info *si,
         if (err)
                 return err;
 
-        seb = kmalloc(sizeof(struct ubi_scan_leb), GFP_KERNEL);
+        seb = kmem_cache_alloc(si->scan_leb_slab, GFP_KERNEL);
         if (!seb)
                 return -ENOMEM;
 
         seb->ec = ec;
         seb->pnum = pnum;
         seb->lnum = lnum;
-        seb->sqnum = sqnum;
         seb->scrub = bitflips;
+        seb->copy_flag = vid_hdr->copy_flag;
+        seb->sqnum = sqnum;
 
         if (sv->highest_lnum <= lnum) {
                 sv->highest_lnum = lnum;
@@ -521,7 +586,6 @@ int ubi_scan_add_used(struct ubi_device *ubi, struct ubi_scan_info *si,
         sv->leb_count += 1;
         rb_link_node(&seb->u.rb, parent, p);
         rb_insert_color(&seb->u.rb, &sv->root);
-        si->used_peb_count += 1;
         return 0;
 }
 
@@ -668,8 +732,8 @@ out_free:
 struct ubi_scan_leb *ubi_scan_get_free_peb(struct ubi_device *ubi,
                                            struct ubi_scan_info *si)
 {
-        int err = 0, i;
-        struct ubi_scan_leb *seb;
+        int err = 0;
+        struct ubi_scan_leb *seb, *tmp_seb;
 
         if (!list_empty(&si->free)) {
                 seb = list_entry(si->free.next, struct ubi_scan_leb, u.list);
@@ -678,38 +742,88 @@ struct ubi_scan_leb *ubi_scan_get_free_peb(struct ubi_device *ubi,
                 return seb;
         }
 
-        for (i = 0; i < 2; i++) {
-                struct list_head *head;
-                struct ubi_scan_leb *tmp_seb;
+        /*
+         * We try to erase the first physical eraseblock from the erase list
+         * and pick it if we succeed, or try to erase the next one if not. And
+         * so forth. We don't want to take care about bad eraseblocks here -
+         * they'll be handled later.
+         */
+        list_for_each_entry_safe(seb, tmp_seb, &si->erase, u.list) {
+                if (seb->ec == UBI_SCAN_UNKNOWN_EC)
+                        seb->ec = si->mean_ec;
 
-                if (i == 0)
-                        head = &si->erase;
-                else
-                        head = &si->corr;
+                err = ubi_scan_erase_peb(ubi, si, seb->pnum, seb->ec+1);
+                if (err)
+                        continue;
 
+                seb->ec += 1;
+                list_del(&seb->u.list);
+                dbg_bld("return PEB %d, EC %d", seb->pnum, seb->ec);
+                return seb;
+        }
+
+        ubi_err("no free eraseblocks");
+        return ERR_PTR(-ENOSPC);
+}
+
+/**
+ * check_corruption - check the data area of PEB.
+ * @ubi: UBI device description object
+ * @vid_hrd: the (corrupted) VID header of this PEB
+ * @pnum: the physical eraseblock number to check
+ *
+ * This is a helper function which is used to distinguish between VID header
+ * corruptions caused by power cuts and other reasons. If the PEB contains only
+ * 0xFF bytes in the data area, the VID header is most probably corrupted
+ * because of a power cut (%0 is returned in this case). Otherwise, it was
+ * probably corrupted for some other reasons (%1 is returned in this case). A
+ * negative error code is returned if a read error occurred.
+ *
+ * If the corruption reason was a power cut, UBI can safely erase this PEB.
+ * Otherwise, it should preserve it to avoid possibly destroying important
+ * information.
+ */
+static int check_corruption(struct ubi_device *ubi, struct ubi_vid_hdr *vid_hdr,
+                            int pnum)
+{
+        int err;
+
+        mutex_lock(&ubi->buf_mutex);
+        memset(ubi->peb_buf1, 0x00, ubi->leb_size);
+
+        err = ubi_io_read(ubi, ubi->peb_buf1, pnum, ubi->leb_start,
+                          ubi->leb_size);
+        if (err == UBI_IO_BITFLIPS || err == -EBADMSG) {
                 /*
-                 * We try to erase the first physical eraseblock from the @head
-                 * list and pick it if we succeed, or try to erase the
-                 * next one if not. And so forth. We don't want to take care
-                 * about bad eraseblocks here - they'll be handled later.
+                 * Bit-flips or integrity errors while reading the data area.
+                 * It is difficult to say for sure what type of corruption is
+                 * this, but presumably a power cut happened while this PEB was
+                 * erased, so it became unstable and corrupted, and should be
+                 * erased.
                  */
-                list_for_each_entry_safe(seb, tmp_seb, head, u.list) {
-                        if (seb->ec == UBI_SCAN_UNKNOWN_EC)
-                                seb->ec = si->mean_ec;
+                err = 0;
+                goto out_unlock;
+        }
 
-                        err = ubi_scan_erase_peb(ubi, si, seb->pnum, seb->ec+1);
-                        if (err)
-                                continue;
+        if (err)
+                goto out_unlock;
 
-                        seb->ec += 1;
-                        list_del(&seb->u.list);
-                        dbg_bld("return PEB %d, EC %d", seb->pnum, seb->ec);
-                        return seb;
-                }
-        }
+        if (ubi_check_pattern(ubi->peb_buf1, 0xFF, ubi->leb_size))
+                goto out_unlock;
 
-        ubi_err("no eraseblocks found");
-        return ERR_PTR(-ENOSPC);
+        ubi_err("PEB %d contains corrupted VID header, and the data does not "
+                "contain all 0xFF, this may be a non-UBI PEB or a severe VID "
+                "header corruption which requires manual inspection", pnum);
+        ubi_dbg_dump_vid_hdr(vid_hdr);
+        dbg_msg("hexdump of PEB %d offset %d, length %d",
+                pnum, ubi->leb_start, ubi->leb_size);
+        ubi_dbg_print_hex_dump(KERN_DEBUG, "", DUMP_PREFIX_OFFSET, 32, 1,
+                               ubi->peb_buf1, ubi->leb_size, 1);
+        err = 1;
+
+out_unlock:
+        mutex_unlock(&ubi->buf_mutex);
+        return err;
 }
 
 /**
@@ -725,7 +839,7 @@ static int process_eb(struct ubi_device *ubi, struct ubi_scan_info *si,
                       int pnum)
 {
         long long uninitialized_var(ec);
-        int err, bitflips = 0, vol_id, ec_corr = 0;
+        int err, bitflips = 0, vol_id, ec_err = 0;
 
         dbg_bld("scan PEB %d", pnum);
 
@@ -746,22 +860,37 @@ static int process_eb(struct ubi_device *ubi, struct ubi_scan_info *si,
         err = ubi_io_read_ec_hdr(ubi, pnum, ech, 0);
         if (err < 0)
                 return err;
-        else if (err == UBI_IO_BITFLIPS)
+        switch (err) {
+        case 0:
+                break;
+        case UBI_IO_BITFLIPS:
                 bitflips = 1;
-        else if (err == UBI_IO_PEB_EMPTY)
-                return add_to_list(si, pnum, UBI_SCAN_UNKNOWN_EC, &si->erase);
-        else if (err == UBI_IO_BAD_HDR_READ || err == UBI_IO_BAD_HDR) {
+                break;
+        case UBI_IO_FF:
+                si->empty_peb_count += 1;
+                return add_to_list(si, pnum, UBI_SCAN_UNKNOWN_EC, 0,
+                                   &si->erase);
+        case UBI_IO_FF_BITFLIPS:
+                si->empty_peb_count += 1;
+                return add_to_list(si, pnum, UBI_SCAN_UNKNOWN_EC, 1,
+                                   &si->erase);
+        case UBI_IO_BAD_HDR_EBADMSG:
+        case UBI_IO_BAD_HDR:
                 /*
                  * We have to also look at the VID header, possibly it is not
                  * corrupted. Set %bitflips flag in order to make this PEB be
                  * moved and EC be re-created.
                  */
-                ec_corr = err;
+                ec_err = err;
                 ec = UBI_SCAN_UNKNOWN_EC;
                 bitflips = 1;
+                break;
+        default:
+                ubi_err("'ubi_io_read_ec_hdr()' returned unknown code %d", err);
+                return -EINVAL;
         }
 
-        if (!ec_corr) {
+        if (!ec_err) {
                 int image_seq;
 
                 /* Make sure UBI version is OK */
@@ -814,24 +943,71 @@ static int process_eb(struct ubi_device *ubi, struct ubi_scan_info *si,
         err = ubi_io_read_vid_hdr(ubi, pnum, vidh, 0);
         if (err < 0)
                 return err;
-        else if (err == UBI_IO_BITFLIPS)
+        switch (err) {
+        case 0:
+                break;
+        case UBI_IO_BITFLIPS:
                 bitflips = 1;
-        else if (err == UBI_IO_BAD_HDR_READ || err == UBI_IO_BAD_HDR ||
-                 (err == UBI_IO_PEB_FREE && ec_corr)) {
-                /* VID header is corrupted */
-                if (err == UBI_IO_BAD_HDR_READ ||
-                    ec_corr == UBI_IO_BAD_HDR_READ)
-                        si->read_err_count += 1;
-                err = add_to_list(si, pnum, ec, &si->corr);
+                break;
+        case UBI_IO_BAD_HDR_EBADMSG:
+                if (ec_err == UBI_IO_BAD_HDR_EBADMSG)
+                        /*
+                         * Both EC and VID headers are corrupted and were read
+                         * with data integrity error, probably this is a bad
+                         * PEB, bit it is not marked as bad yet. This may also
+                         * be a result of power cut during erasure.
+                         */
+                        si->maybe_bad_peb_count += 1;
+        case UBI_IO_BAD_HDR:
+                if (ec_err)
+                        /*
+                         * Both headers are corrupted. There is a possibility
+                         * that this a valid UBI PEB which has corresponding
+                         * LEB, but the headers are corrupted. However, it is
+                         * impossible to distinguish it from a PEB which just
+                         * contains garbage because of a power cut during erase
+                         * operation. So we just schedule this PEB for erasure.
+                         *
+                         * Besides, in case of NOR flash, we deliberately
+                         * corrupt both headers because NOR flash erasure is
+                         * slow and can start from the end.
+                         */
+                        err = 0;
+                else
+                        /*
+                         * The EC was OK, but the VID header is corrupted. We
+                         * have to check what is in the data area.
+                         */
+                        err = check_corruption(ubi, vidh, pnum);
+
+                if (err < 0)
+                        return err;
+                else if (!err)
+                        /* This corruption is caused by a power cut */
+                        err = add_to_list(si, pnum, ec, 1, &si->erase);
+                else
+                        /* This is an unexpected corruption */
+                        err = add_corrupted(si, pnum, ec);
+                if (err)
+                        return err;
+                goto adjust_mean_ec;
+        case UBI_IO_FF_BITFLIPS:
+                err = add_to_list(si, pnum, ec, 1, &si->erase);
                 if (err)
                         return err;
                 goto adjust_mean_ec;
-        } else if (err == UBI_IO_PEB_FREE) {
-                /* No VID header - the physical eraseblock is free */
-                err = add_to_list(si, pnum, ec, &si->free);
+        case UBI_IO_FF:
+                if (ec_err)
+                        err = add_to_list(si, pnum, ec, 1, &si->erase);
+                else
+                        err = add_to_list(si, pnum, ec, 0, &si->free);
                 if (err)
                         return err;
                 goto adjust_mean_ec;
+        default:
+                ubi_err("'ubi_io_read_vid_hdr()' returned unknown code %d",
+                        err);
+                return -EINVAL;
         }
 
         vol_id = be32_to_cpu(vidh->vol_id);
@@ -843,7 +1019,7 @@ static int process_eb(struct ubi_device *ubi, struct ubi_scan_info *si,
                 case UBI_COMPAT_DELETE:
                         ubi_msg("\"delete\" compatible internal volume %d:%d"
                                 " found, will remove it", vol_id, lnum);
-                        err = add_to_list(si, pnum, ec, &si->erase);
+                        err = add_to_list(si, pnum, ec, 1, &si->erase);
                         if (err)
                                 return err;
                         return 0;
@@ -858,7 +1034,7 @@ static int process_eb(struct ubi_device *ubi, struct ubi_scan_info *si,
                 case UBI_COMPAT_PRESERVE:
                         ubi_msg("\"preserve\" compatible internal volume %d:%d"
                                 " found", vol_id, lnum);
-                        err = add_to_list(si, pnum, ec, &si->alien);
+                        err = add_to_list(si, pnum, ec, 0, &si->alien);
                         if (err)
                                 return err;
                         return 0;
@@ -870,7 +1046,7 @@ static int process_eb(struct ubi_device *ubi, struct ubi_scan_info *si,
                 }
         }
 
-        if (ec_corr)
+        if (ec_err)
                 ubi_warn("valid VID header but corrupted EC header at PEB %d",
                          pnum);
         err = ubi_scan_add_used(ubi, si, pnum, ec, vidh, bitflips);
@@ -878,7 +1054,7 @@ static int process_eb(struct ubi_device *ubi, struct ubi_scan_info *si,
                 return err;
 
 adjust_mean_ec:
-        if (!ec_corr) {
+        if (!ec_err) {
                 si->ec_sum += ec;
                 si->ec_count += 1;
                 if (ec > si->max_ec)
@@ -904,19 +1080,20 @@ adjust_mean_ec:
 static int check_what_we_have(struct ubi_device *ubi, struct ubi_scan_info *si)
 {
         struct ubi_scan_leb *seb;
-        int max_corr;
+        int max_corr, peb_count;
 
-        max_corr = ubi->peb_count - si->bad_peb_count - si->alien_peb_count;
-        max_corr = max_corr / 20 ?: 8;
+        peb_count = ubi->peb_count - si->bad_peb_count - si->alien_peb_count;
+        max_corr = peb_count / 20 ?: 8;
 
         /*
-         * Few corrupted PEBs are not a problem and may be just a result of
+         * Few corrupted PEBs is 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:");
+        if (si->corr_peb_count) {
+                ubi_err("%d PEBs are corrupted and preserved",
+                        si->corr_peb_count);
+                printk(KERN_ERR "Corrupted PEBs are:");
                 list_for_each_entry(seb, &si->corr, u.list)
                         printk(KERN_CONT " %d", seb->pnum);
                 printk(KERN_CONT "\n");
@@ -926,46 +1103,40 @@ static int check_what_we_have(struct ubi_device *ubi, struct ubi_scan_info *si)
                  * otherwise, only print a warning.
                  */
                 if (si->corr_peb_count >= max_corr) {
-                        ubi_err("too many corrupted PEBs, refusing this device");
+                        ubi_err("too many corrupted PEBs, refusing");
                         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).
-                         */
+        if (si->empty_peb_count + si->maybe_bad_peb_count == peb_count) {
+                /*
+                 * All PEBs are empty, or almost all - a couple PEBs look like
+                 * they may be bad PEBs which were not marked as bad yet.
+                 *
+                 * This piece of code basically tries to distinguish between
+                 * the following 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 formatting,
+                 *    the faulty PEBs will probably be marked as bad.
+                 *
+                 * 2. Flash contains non-UBI data and we do not want to format
+                 *    it and destroy possibly important information.
+                 */
+                if (si->maybe_bad_peb_count <= 2) {
                         si->is_empty = 1;
                         ubi_msg("empty MTD device detected");
-                        get_random_bytes(&ubi->image_seq, sizeof(ubi->image_seq));
+                        get_random_bytes(&ubi->image_seq,
+                                         sizeof(ubi->image_seq));
                 } else {
-                        ubi_err("MTD device possibly contains non-UBI data, "
-                                "refusing it");
+                        ubi_err("MTD device is not UBI-formatted and possibly "
+                                "contains non-UBI data - refusing it");
                         return -EINVAL;
                 }
+
         }
 
-        if (si->corr_peb_count > 0)
-                ubi_msg("corrupted PEBs will be formatted");
         return 0;
 }
 
@@ -995,9 +1166,15 @@ struct ubi_scan_info *ubi_scan(struct ubi_device *ubi)
         si->volumes = RB_ROOT;
 
         err = -ENOMEM;
+        si->scan_leb_slab = kmem_cache_create("ubi_scan_leb_slab",
+                                              sizeof(struct ubi_scan_leb),
+                                              0, 0, NULL);
+        if (!si->scan_leb_slab)
+                goto out_si;
+
         ech = kzalloc(ubi->ec_hdr_alsize, GFP_KERNEL);
         if (!ech)
-                goto out_si;
+                goto out_slab;
 
         vidh = ubi_zalloc_vid_hdr(ubi, GFP_KERNEL);
         if (!vidh)
@@ -1058,6 +1235,8 @@ out_vidh:
         ubi_free_vid_hdr(ubi, vidh);
 out_ech:
         kfree(ech);
+out_slab:
+        kmem_cache_destroy(si->scan_leb_slab);
 out_si:
         ubi_scan_destroy_si(si);
         return ERR_PTR(err);
@@ -1066,11 +1245,12 @@ out_si:
 /**
  * destroy_sv - free the scanning volume information
  * @sv: scanning volume information
+ * @si: scanning information
  *
  * This function destroys the volume RB-tree (@sv->root) and the scanning
  * volume information.
  */
-static void destroy_sv(struct ubi_scan_volume *sv)
+static void destroy_sv(struct ubi_scan_info *si, struct ubi_scan_volume *sv)
 {
         struct ubi_scan_leb *seb;
         struct rb_node *this = sv->root.rb_node;
@@ -1090,7 +1270,7 @@ static void destroy_sv(struct ubi_scan_volume *sv)
                                         this->rb_right = NULL;
                         }
 
-                        kfree(seb);
+                        kmem_cache_free(si->scan_leb_slab, seb);
                 }
         }
         kfree(sv);
@@ -1108,19 +1288,19 @@ void ubi_scan_destroy_si(struct ubi_scan_info *si)
 
         list_for_each_entry_safe(seb, seb_tmp, &si->alien, u.list) {
                 list_del(&seb->u.list);
-                kfree(seb);
+                kmem_cache_free(si->scan_leb_slab, seb);
         }
         list_for_each_entry_safe(seb, seb_tmp, &si->erase, u.list) {
                 list_del(&seb->u.list);
-                kfree(seb);
+                kmem_cache_free(si->scan_leb_slab, seb);
         }
         list_for_each_entry_safe(seb, seb_tmp, &si->corr, u.list) {
                 list_del(&seb->u.list);
-                kfree(seb);
+                kmem_cache_free(si->scan_leb_slab, seb);
         }
         list_for_each_entry_safe(seb, seb_tmp, &si->free, u.list) {
                 list_del(&seb->u.list);
-                kfree(seb);
+                kmem_cache_free(si->scan_leb_slab, seb);
         }
 
         /* Destroy the volume RB-tree */
@@ -1141,14 +1321,15 @@ void ubi_scan_destroy_si(struct ubi_scan_info *si)
                                         rb->rb_right = NULL;
                         }
 
-                        destroy_sv(sv);
+                        destroy_sv(si, sv);
                 }
         }
 
+        kmem_cache_destroy(si->scan_leb_slab);
         kfree(si);
 }
 
-#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID
+#ifdef CONFIG_MTD_UBI_DEBUG
 
 /**
  * paranoid_check_si - check the scanning information.
@@ -1166,6 +1347,9 @@ static int paranoid_check_si(struct ubi_device *ubi, struct ubi_scan_info *si)
         struct ubi_scan_leb *seb, *last_seb;
         uint8_t *buf;
 
+        if (!(ubi_chk_flags & UBI_CHK_GEN))
+                return 0;
+
         /*
          * At first, check that scanning information is OK.
          */
@@ -1418,4 +1602,4 @@ out:
         return -EINVAL;
 }
 
-#endif /* CONFIG_MTD_UBI_DEBUG_PARANOID */
+#endif /* CONFIG_MTD_UBI_DEBUG */