| From 1900149c835ab5b48bea31a823ea5e5a401fb560 Mon Sep 17 00:00:00 2001 |
| From: Richard Weinberger <richard@nod.at> |
| Date: Tue, 26 Apr 2016 16:39:48 +0200 |
| Subject: UBI: Fix static volume checks when Fastmap is used |
| |
| From: Richard Weinberger <richard@nod.at> |
| |
| commit 1900149c835ab5b48bea31a823ea5e5a401fb560 upstream. |
| |
| 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. |
| |
| Reported-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar> |
| Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar> |
| Signed-off-by: Richard Weinberger <richard@nod.at> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| drivers/mtd/ubi/eba.c | 21 +++++++++++++++++++-- |
| drivers/mtd/ubi/fastmap.c | 1 + |
| drivers/mtd/ubi/ubi.h | 2 ++ |
| 3 files changed, 22 insertions(+), 2 deletions(-) |
| |
| --- a/drivers/mtd/ubi/eba.c |
| +++ b/drivers/mtd/ubi/eba.c |
| @@ -426,8 +426,25 @@ retry: |
| pnum, vol_id, lnum); |
| err = -EBADMSG; |
| } else { |
| - err = -EINVAL; |
| - ubi_ro_mode(ubi); |
| + /* |
| + * Ending up here in the non-Fastmap case |
| + * is a clear bug as the VID header had to |
| + * be present at scan time to have it referenced. |
| + * With fastmap the story is more complicated. |
| + * Fastmap has the mapping info without the need |
| + * of a full scan. So the LEB could have been |
| + * unmapped, Fastmap cannot know this and keeps |
| + * the LEB referenced. |
| + * This is valid and works as the layer above UBI |
| + * has to do bookkeeping about used/referenced |
| + * LEBs in any case. |
| + */ |
| + if (ubi->fast_attach) { |
| + err = -EBADMSG; |
| + } else { |
| + err = -EINVAL; |
| + ubi_ro_mode(ubi); |
| + } |
| } |
| } |
| goto out_free; |
| --- a/drivers/mtd/ubi/fastmap.c |
| +++ b/drivers/mtd/ubi/fastmap.c |
| @@ -1058,6 +1058,7 @@ int ubi_scan_fastmap(struct ubi_device * |
| ubi_msg(ubi, "fastmap WL pool size: %d", |
| ubi->fm_wl_pool.max_size); |
| ubi->fm_disabled = 0; |
| + ubi->fast_attach = 1; |
| |
| ubi_free_vid_hdr(ubi, vh); |
| kfree(ech); |
| --- a/drivers/mtd/ubi/ubi.h |
| +++ b/drivers/mtd/ubi/ubi.h |
| @@ -466,6 +466,7 @@ struct ubi_debug_info { |
| * @fm_eba_sem: allows ubi_update_fastmap() to block EBA table changes |
| * @fm_work: fastmap work queue |
| * @fm_work_scheduled: non-zero if fastmap work was scheduled |
| + * @fast_attach: non-zero if UBI was attached by fastmap |
| * |
| * @used: RB-tree of used physical eraseblocks |
| * @erroneous: RB-tree of erroneous used physical eraseblocks |
| @@ -574,6 +575,7 @@ struct ubi_device { |
| size_t fm_size; |
| struct work_struct fm_work; |
| int fm_work_scheduled; |
| + int fast_attach; |
| |
| /* Wear-leveling sub-system's stuff */ |
| struct rb_root used; |
