Commit f59ed239 authored Feb 06, 2024 by Zhihao Cheng

ubi: fastmap: may_reserve_for_fm: Don't reserve PEB if fm_anchor exists

mainline inclusion
from mainline-v6.7-rc1
commit eada823e6a6fb856548f6e0c7a343cd5c41bb9d3
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I9195H
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=eada823e6a6fb856548f6e0c7a343cd5c41bb9d3

-------------------------------------------------

This is the part 1 to fix cyclically reusing single fastmap data PEBs.

After running fsstress on UBIFS for a while, UBI (16384 blocks, fastmap
takes 2 blocks) has an erase block(PEB: 8031) with big erase counter
greater than any other pebs:

=========================================================
from              to     count      min      avg      max
---------------------------------------------------------
0        ..        9:        0        0        0        0
10       ..       99:      532       84       92       99
100      ..      999:    15787      100      147      229
1000     ..     9999:       64     4699     4765     4826
10000    ..    99999:        0        0        0        0
100000   ..      inf:        1   272935   272935   272935
---------------------------------------------------------
Total               :    16384       84      180   272935

Not like fm_anchor, there is no candidate PEBs for fastmap data area,
so old fastmap data pebs will be reused after all free pebs are filled
into pool/wl_pool:
ubi_update_fastmap
 for (i = 1; i < new_fm->used_blocks; i++)
  erase_block(ubi, old_fm->e[i]->pnum)
  new_fm->e[i] = old_fm->e[i]

According to wear leveling algorithm, UBI selects one small erase
counter PEB from ubi->used and one big erase counter PEB from wl_pool,
the reused fastmap data PEB is not in these trees. UBI won't schedule
this PEB for wl even it is in ubi->used because wl algorithm expects
small erase counter for used PEB.

Don't reserve PEB for fastmap in may_reserve_for_fm() if fm_anchor
already exists. Otherwise, when UBI is running out of free PEBs,
the only one free PEB (pnum < 64) will be skipped and fastmap data
will be written on the same old PEB.

Fixes: dbb7d2a8 ("UBI: Add fastmap core")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217787


Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

parent c0eebecd

drivers/mtd/ubi/fastmap-wl.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -521,7 +521,7 @@ static void ubi_fastmap_close(struct ubi_device *ubi)
		static struct ubi_wl_entry may_reserve_for_fm(struct ubi_device ubi,
		struct ubi_wl_entry *e,
		struct rb_root *root) {
		if (e && !ubi->fm_disabled && !ubi->fm &&
		if (e && !ubi->fm_disabled && !ubi->fm && !ubi->fm_anchor &&
		e->pnum < UBI_FM_MAX_START)
		e = rb_entry(rb_next(root->rb_node),
		struct ubi_wl_entry, u.rb);

drivers/mtd/ubi/wl.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -367,9 +367,12 @@ static struct ubi_wl_entry find_mean_wl_entry(struct ubi_device ubi,
		if (last->ec - first->ec < WL_FREE_MAX_DIFF) {
		e = rb_entry(root->rb_node, struct ubi_wl_entry, u.rb);

		/* If no fastmap has been written and this WL entry can be used
		* as anchor PEB, hold it back and return the second best
		* WL entry such that fastmap can use the anchor PEB later. */
		/*
		* If no fastmap has been written and fm_anchor is not
		* reserved and this WL entry can be used as anchor PEB
		* hold it back and return the second best WL entry such
		* that fastmap can use the anchor PEB later.
		*/
		e = may_reserve_for_fm(ubi, e, root);
		} else
		e = find_wl_entry(ubi, root, WL_FREE_MAX_DIFF/2);