UBI : Atomic change LEB
Artem Bityutskiy
dedekind at infradead.org
Thu Sep 13 07:13:52 EDT 2007
Hi,
On Thu, 2007-09-13 at 13:32 +0530, Brijesh Singh wrote:
> I think there is a problem in atomic change LEB.
> I was trying to think how ubi will behave when device is full.
> Suppose device is full.And
> LEBn maps to pebn
> i.e. Ln->pn
> If we used automic_change_leb, wear-levelling has no free blocks as
> all lebs are mapped to pebs.And no change in LEB is possible to any
> LEB.
> I think we will need atleast one extra block at any instance of time
> to avoid this situation.
> This is similar to block movement situation where we need extra block
> for block movement.
yeah, you are right, thank you! The below patch should fix the problem.
Comments?
>From f02c2e8a10838d80c763f6ccd65398cccd3cfac0 Mon Sep 17 00:00:00 2001
From: Artem Bityutskiy <Artem.Bityutskiy at nokia.com>
Date: Thu, 13 Sep 2007 14:28:14 +0300
Subject: [PATCH] UBI: fix atomic LEB change problems
When the UBI device is nearly full, i.e. all LEBs are mapped, we have
only one spare LEB left - the one we reserved for WL purposes. Well,
I do not count the LEBs which were reserved for bad PEB handling -
suppose NOR flash for simplicity. If an "atomic LEB change operation"
is run, and the WL unit is moving a LEB, we have no spare LEBs to
finish the operation and fail, which is not good. Moreover, if there
are 2 or more simultanious "atomic LEB change" requests, only one of
them has chances to succeed, the other will fail with -ENOSPC. Not
good either.
This patch does 2 things:
1. Reserves one PEB for the "atomic LEB change" operation.
2. Serealize the operations so that only on of them may run
at a time (by means of a mutex).
Pointed-to-by: Brijesh Singh <brijesh.s.singh at gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy at nokia.com>
---
drivers/mtd/ubi/eba.c | 48 +++++++++++++++++++++++++++++-------------------
drivers/mtd/ubi/ubi.h | 6 ++++--
2 files changed, 33 insertions(+), 21 deletions(-)
diff --git a/drivers/mtd/ubi/eba.c b/drivers/mtd/ubi/eba.c
index 81bb6a3..7b7add6 100644
--- a/drivers/mtd/ubi/eba.c
+++ b/drivers/mtd/ubi/eba.c
@@ -46,6 +46,9 @@
#include <linux/err.h>
#include "ubi.h"
+/* Number of physical eraseblocks reserved for atomic LEB change operation */
+#define EBA_RESERVED_PEBS 1
+
/**
* struct ltree_entry - an entry in the lock tree.
* @rb: links RB-tree nodes
@@ -827,6 +830,9 @@ write_error:
* data, which has to be aligned. This function guarantees that in case of an
* unclean reboot the old contents is preserved. Returns zero in case of
* success and a negative error code in case of failure.
+ *
+ * UBI reserves one LEB for the "atomic LEB change" operation, so only one
+ * LEB change may be done at a time. This is ensured by @ubi->alc_mutex.
*/
int ubi_eba_atomic_leb_change(struct ubi_device *ubi, int vol_id, int lnum,
const void *buf, int len, int dtype)
@@ -843,11 +849,10 @@ int ubi_eba_atomic_leb_change(struct ubi_device *ubi, int vol_id, int lnum,
if (!vid_hdr)
return -ENOMEM;
+ mutex_lock(&ubi->alc_mutex);
err = leb_write_lock(ubi, vol_id, lnum);
- if (err) {
- ubi_free_vid_hdr(ubi, vid_hdr);
- return err;
- }
+ if (err)
+ goto out_mutex;
vid_hdr->sqnum = cpu_to_be64(next_sqnum(ubi));
vid_hdr->vol_id = cpu_to_be32(vol_id);
@@ -864,9 +869,8 @@ int ubi_eba_atomic_leb_change(struct ubi_device *ubi, int vol_id, int lnum,
retry:
pnum = ubi_wl_get_peb(ubi, dtype);
if (pnum < 0) {
- ubi_free_vid_hdr(ubi, vid_hdr);
- leb_write_unlock(ubi, vol_id, lnum);
- return pnum;
+ err = pnum;
+ goto out_leb_unlock;
}
dbg_eba("change LEB %d:%d, PEB %d, write VID hdr to PEB %d",
@@ -888,17 +892,18 @@ retry:
if (vol->eba_tbl[lnum] >= 0) {
err = ubi_wl_put_peb(ubi, vol->eba_tbl[lnum], 1);
- if (err) {
- ubi_free_vid_hdr(ubi, vid_hdr);
- leb_write_unlock(ubi, vol_id, lnum);
- return err;
- }
+ if (err)
+ goto out_leb_unlock;
}
vol->eba_tbl[lnum] = pnum;
+
+out_leb_unlock:
leb_write_unlock(ubi, vol_id, lnum);
+out_mutex:
+ mutex_unlock(&ubi->alc_mutex);
ubi_free_vid_hdr(ubi, vid_hdr);
- return 0;
+ return err;
write_error:
if (err != -EIO || !ubi->bad_allowed) {
@@ -908,17 +913,13 @@ write_error:
* mode just in case.
*/
ubi_ro_mode(ubi);
- leb_write_unlock(ubi, vol_id, lnum);
- ubi_free_vid_hdr(ubi, vid_hdr);
- return err;
+ goto out_leb_unlock;
}
err = ubi_wl_put_peb(ubi, pnum, 1);
if (err || ++tries > UBI_IO_RETRIES) {
ubi_ro_mode(ubi);
- leb_write_unlock(ubi, vol_id, lnum);
- ubi_free_vid_hdr(ubi, vid_hdr);
- return err;
+ goto out_leb_unlock;
}
vid_hdr->sqnum = cpu_to_be64(next_sqnum(ubi));
@@ -1122,6 +1123,7 @@ int ubi_eba_init_scan(struct ubi_device *ubi, struct ubi_scan_info *si)
dbg_eba("initialize EBA unit");
spin_lock_init(&ubi->ltree_lock);
+ mutex_init(&ubi->alc_mutex);
ubi->ltree = RB_ROOT;
if (ubi_devices_cnt == 0) {
@@ -1183,6 +1185,14 @@ int ubi_eba_init_scan(struct ubi_device *ubi, struct ubi_scan_info *si)
ubi->rsvd_pebs += ubi->beb_rsvd_pebs;
}
+ if (ubi->avail_pebs < EBA_RESERVED_PEBS) {
+ ubi_err("no enough physical eraseblocks (%d, need %d)",
+ ubi->avail_pebs, EBA_RESERVED_PEBS);
+ goto out_free;
+ }
+ ubi->avail_pebs -= EBA_RESERVED_PEBS;
+ ubi->rsvd_pebs += EBA_RESERVED_PEBS;
+
dbg_eba("EBA unit is initialized");
return 0;
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index cc01011..5e941a6 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -221,14 +221,15 @@ struct ubi_wl_entry;
* @vtbl_slots: how many slots are available in the volume table
* @vtbl_size: size of the volume table in bytes
* @vtbl: in-RAM volume table copy
+ * @vtbl_mutex: protects on-flash volume table
*
* @max_ec: current highest erase counter value
* @mean_ec: current mean erase counter value
*
- * global_sqnum: global sequence number
+ * @global_sqnum: global sequence number
* @ltree_lock: protects the lock tree and @global_sqnum
* @ltree: the lock tree
- * @vtbl_mutex: protects on-flash volume table
+ * @alc_mutex: serializes "atomic LEB change" operations
*
* @used: RB-tree of used physical eraseblocks
* @free: RB-tree of free physical eraseblocks
@@ -308,6 +309,7 @@ struct ubi_device {
unsigned long long global_sqnum;
spinlock_t ltree_lock;
struct rb_root ltree;
+ struct mutex alc_mutex;
/* Wear-leveling unit's stuff */
struct rb_root used;
--
1.5.0.6
--
Best regards,
Artem Bityutskiy (Битюцкий Артём)
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