linux/drivers/mtd
Richard Weinberger 1900149c83 UBI: Fix static volume checks when Fastmap is used
Ezequiel reported that he's facing UBI going into read-only
mode after power cut. It turned out that this behavior happens
only when updating a static volume is interrupted and Fastmap is
used.

A possible trace can look like:
ubi0 warning: ubi_io_read_vid_hdr [ubi]: no VID header found at PEB 2323, only 0xFF bytes
ubi0 warning: ubi_eba_read_leb [ubi]: switch to read-only mode
CPU: 0 PID: 833 Comm: ubiupdatevol Not tainted 4.6.0-rc2-ARCH #4
Hardware name: SAMSUNG ELECTRONICS CO., LTD. 300E4C/300E5C/300E7C/NP300E5C-AD8AR, BIOS P04RAP 10/15/2012
0000000000000286 00000000eba949bd ffff8800c45a7b38 ffffffff8140d841
ffff8801964be000 ffff88018eaa4800 ffff8800c45a7bb8 ffffffffa003abf6
ffffffff850e2ac0 8000000000000163 ffff8801850e2ac0 ffff8801850e2ac0
Call Trace:
[<ffffffff8140d841>] dump_stack+0x63/0x82
[<ffffffffa003abf6>] ubi_eba_read_leb+0x486/0x4a0 [ubi]
[<ffffffffa00453b3>] ubi_check_volume+0x83/0xf0 [ubi]
[<ffffffffa0039d97>] ubi_open_volume+0x177/0x350 [ubi]
[<ffffffffa00375d8>] vol_cdev_open+0x58/0xb0 [ubi]
[<ffffffff8124b08e>] chrdev_open+0xae/0x1d0
[<ffffffff81243bcf>] do_dentry_open+0x1ff/0x300
[<ffffffff8124afe0>] ? cdev_put+0x30/0x30
[<ffffffff81244d36>] vfs_open+0x56/0x60
[<ffffffff812545f4>] path_openat+0x4f4/0x1190
[<ffffffff81256621>] do_filp_open+0x91/0x100
[<ffffffff81263547>] ? __alloc_fd+0xc7/0x190
[<ffffffff812450df>] do_sys_open+0x13f/0x210
[<ffffffff812451ce>] SyS_open+0x1e/0x20
[<ffffffff81a99e32>] entry_SYSCALL_64_fastpath+0x1a/0xa4

UBI checks static volumes for data consistency and reads the
whole volume upon first open. If the volume is found erroneous
users of UBI cannot read from it, but another volume update is
possible to fix it. The check is performed by running
ubi_eba_read_leb() on every allocated LEB of the volume.
For static volumes ubi_eba_read_leb() computes the checksum of all
data stored in a LEB. To verify the computed checksum it has to read
the LEB's volume header which stores the original checksum.
If the volume header is not found UBI treats this as fatal internal
error and switches to RO mode. If the UBI device was attached via a
full scan the assumption is correct, the volume header has to be
present as it had to be there while scanning to get known as mapped.
If the attach operation happened via Fastmap the assumption is no
longer correct. When attaching via Fastmap UBI learns the mapping
table from Fastmap's snapshot of the system state and not via a full
scan. It can happen that a LEB got unmapped after a Fastmap was
written to the flash. Then UBI can learn the LEB still as mapped and
accessing it returns only 0xFF bytes. As UBI is not a FTL it is
allowed to have mappings to empty PEBs, it assumes that the layer
above takes care of LEB accounting and referencing.
UBIFS does so using the LEB property tree (LPT).
For static volumes UBI blindly assumes that all LEBs are present and
therefore special actions have to be taken.

The described situation can happen when updating a static volume is
interrupted, either by a user or a power cut.
The volume update code first unmaps all LEBs of a volume and then
writes LEB by LEB. If the sequence of operations is interrupted UBI
detects this either by the absence of LEBs, no volume header present
at scan time, or corrupted payload, detected via checksum.
In the Fastmap case the former method won't trigger as no scan
happened and UBI automatically thinks all LEBs are present.
Only by reading data from a LEB it detects that the volume header is
missing and incorrectly treats this as fatal error.
To deal with the situation ubi_eba_read_leb() from now on checks
whether we attached via Fastmap and handles the absence of a
volume header like a data corruption error.
This way interrupted static volume updates will correctly get detected
also when Fastmap is used.

Cc: <stable@vger.kernel.org>
Reported-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Richard Weinberger <richard@nod.at>
2016-05-24 15:24:37 +02:00
..
chips mtd: cfi_cmdset_0001: fixing memory leak and handling failed kmalloc 2016-01-06 17:23:10 -08:00
devices mm, fs: get rid of PAGE_CACHE_* and page_cache_{get,release} macros 2016-04-04 10:41:08 -07:00
lpddr mtd: lpddr: show parent device in sysfs 2015-10-13 09:21:17 -07:00
maps MTD updates for v4.5: 2016-01-13 11:25:54 -08:00
nand One MTD fix for v4.6-rc4: 2016-04-15 15:25:09 -07:00
onenand MTD updates for v4.6 2016-03-24 19:57:15 -07:00
spi-nor mtd: spi-nor: support lock/unlock for a few Winbond chips 2016-03-07 18:01:58 -08:00
tests MTD updates for v4.6 2016-03-24 19:57:15 -07:00
ubi UBI: Fix static volume checks when Fastmap is used 2016-05-24 15:24:37 +02:00
afs.c mtd: partitions: make parsers return 'const' partition arrays 2015-12-09 10:21:57 -08:00
ar7part.c mtd: partitions: make parsers return 'const' partition arrays 2015-12-09 10:21:57 -08:00
bcm47xxpart.c mtd: bcm47xxpart: don't fail because of bit-flips 2016-01-23 14:40:47 -08:00
bcm63xxpart.c mtd: bcm63xxpart: give width specifier an 'int', not 'size_t' 2016-03-07 13:13:58 -08:00
cmdlinepart.c mtd: partitions: make parsers return 'const' partition arrays 2015-12-09 10:21:57 -08:00
ftl.c mtd: ftl: use swap() in copy_erase_unit() 2015-12-18 16:56:07 -08:00
inftlcore.c
inftlmount.c mtd: intflmount: fix off by one error in INFTL_dumpVUchains() 2014-11-05 13:19:21 -08:00
Kconfig mtd: bcm63xxpart: Remove dependency on mach-bcm63xx 2016-02-12 10:27:48 -08:00
Makefile mtd: spi-nor: shorten Kconfig naming 2014-04-14 11:23:01 -07:00
mtd_blkdevs.c mtd: blkdevs: fix potential deadlock + lockdep warnings 2015-10-30 17:24:43 -07:00
mtdblock_ro.c
mtdblock.c mtd: mtdblock: remove the needless mtdblks_lock 2015-01-07 12:51:56 -08:00
mtdchar.c mtd: provide proper 32/64-bit compat_ioctl() support for BLKPG 2015-09-29 13:37:04 -07:00
mtdconcat.c MTD updates for 3.20-rc1 2015-02-18 08:01:44 -08:00
mtdcore.c mtd: merge MTD development from v4.4 into for-v4.5 development 2016-01-05 16:05:56 -08:00
mtdcore.h mtd: partitions: support a cleanup callback for parsers 2015-12-09 14:57:44 -08:00
mtdoops.c
mtdpart.c mtd: create an mtd_oobavail() helper and make use of it 2016-03-07 16:23:09 -08:00
mtdsuper.c
mtdswap.c mtd: mtdswap: remove useless if (!mtd->ecclayout) test 2016-03-07 16:23:09 -08:00
nftlcore.c
nftlmount.c mtd: nftl: reorganize operations in condition check 2015-01-09 15:26:29 -08:00
ofpart.c mtd: partitions: make parsers return 'const' partition arrays 2015-12-09 10:21:57 -08:00
redboot.c mtd: partitions: make parsers return 'const' partition arrays 2015-12-09 10:21:57 -08:00
rfd_ftl.c
sm_ftl.c mtd: sm_ftl: fix wrong do_div() usage 2015-11-16 15:07:16 -08:00
sm_ftl.h
ssfdc.c