kernel.git/drivers/mtd/ubi/fastmap.c, branch linux-4.1.y

UBI: Fix static volume checks when Fastmap is used

2016-06-06T23:12:34Z

[ Upstream commit 1900149c835ab5b48bea31a823ea5e5a401fb560 ] 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: [] dump_stack+0x63/0x82 [] ubi_eba_read_leb+0x486/0x4a0 [ubi] [] ubi_check_volume+0x83/0xf0 [ubi] [] ubi_open_volume+0x177/0x350 [ubi] [] vol_cdev_open+0x58/0xb0 [ubi] [] chrdev_open+0xae/0x1d0 [] do_dentry_open+0x1ff/0x300 [] ? cdev_put+0x30/0x30 [] vfs_open+0x56/0x60 [] path_openat+0x4f4/0x1190 [] do_filp_open+0x91/0x100 [] ? __alloc_fd+0xc7/0x190 [] do_sys_open+0x13f/0x210 [] SyS_open+0x1e/0x20 [] 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: Reported-by: Ezequiel Garcia Tested-by: Ezequiel Garcia Signed-off-by: Richard Weinberger Signed-off-by: Sasha Levin

UBI: Fastmap: Wire up WL accessor functions

2015-03-26T21:47:35Z

Use the new WL accessor functions in fastmap. Signed-off-by: Richard Weinberger

UBI: Fastmap: Add self check to detect absent PEBs

2015-03-26T21:46:05Z

This self check allows Fastmap to detect absent PEBs while writing a new fastmap to the MTD device. It will help to find implementation issues in Fastmap. Signed-off-by: Richard Weinberger

UBI: Fastmap: Rework fastmap error paths

2015-03-26T21:46:03Z

If UBI is unable to write the fastmap to the device we have make sure that upon next attach UBI will fall back to scanning mode. In case we cannot ensure that they only thing we can do is falling back to read-only mode. The current error handling code is not powercut proof. It could happen that a powercut while invalidating would lead to a state where an too old fastmap could be used upon attach. This patch addresses the issue by writing a fake fastmap super block to a fresh PEB instead of reerasing the existing one. The fake fastmap super block will UBI case to do a full scan. Signed-off-by: Richard Weinberger

UBI: Fastmap: Prepare for variable sized fastmaps

2015-03-26T21:46:02Z

The current code assumes that each fastmap has the same amount of PEBs. So far this is true but will change soon. Signed-off-by: Richard Weinberger

UBI: Fastmap: Locking updates

2015-03-26T21:46:02Z

a) Rename ubi->fm_sem to ubi->fm_eba_sem as this semaphore protects EBA changes. b) Turn ubi->fm_mutex into a rw semaphore. It will still serialize fastmap writes but also ensures that ubi_wl_put_peb() is not interrupted by a fastmap write. We use a rw semaphore to allow ubi_wl_put_peb() still to be executed in parallel if no fastmap write is happening. Signed-off-by: Richard Weinberger

UBI: Fastmap: Set used_ebs only for static volumes

2015-03-26T21:46:01Z

If we set it for dynamic ones we might confuse various self checks. Signed-off-by: Richard Weinberger

UBI: Fastmap: Fix leb_count unbalance

2015-03-26T21:46:00Z

If a LEB is unmapped we have to decrement leb_count as well. Signed-off-by: Richard Weinberger

UBI: Fastmap: Switch to ro mode if invalidate_fastmap() fails

2015-03-26T21:45:59Z

We have to switch to ro mode to guarantee that upon next UBI attach all data is consistent. Signed-off-by: Richard Weinberger

UBI: Fastmap: Remove eba_orphans logic

2015-03-26T21:45:59Z

This logic is in vain as we treat protected PEBs also as used, so this case must not happen. If a PEB is found which is in the EBA table but not known as used has to be issued as fatal error. Signed-off-by: Richard Weinberger