[openwrt/openwrt] kernel: mtk_bmt: refactor to avoid deep recursion
LEDE Commits
lede-commits at lists.infradead.org
Sat Apr 29 03:59:53 PDT 2023
ynezz pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/626c84340d54c07f46f6ae111ff4389980a86c64
commit 626c84340d54c07f46f6ae111ff4389980a86c64
Author: Michał Kępień <openwrt at kempniu.pl>
AuthorDate: Sat Apr 29 07:41:32 2023 +0100
kernel: mtk_bmt: refactor to avoid deep recursion
A Linksys E8450 (mt7622) device running current master has recently
started crashing:
[ 0.562900] mtk-ecc 1100e000.ecc: probed
[ 0.570254] spi-nand spi2.0: Fidelix SPI NAND was found.
[ 0.575576] spi-nand spi2.0: 128 MiB, block size: 128 KiB, page size: 2048, OOB size: 64
[ 0.583780] mtk-snand 1100d000.spi: ECC strength: 4 bits per 512 bytes
[ 0.682930] Insufficient stack space to handle exception!
[ 0.682939] ESR: 0x0000000096000047 -- DABT (current EL)
[ 0.682946] FAR: 0xffffffc008c47fe0
[ 0.682948] Task stack: [0xffffffc008c48000..0xffffffc008c4c000]
[ 0.682951] IRQ stack: [0xffffffc008008000..0xffffffc00800c000]
[ 0.682954] Overflow stack: [0xffffff801feb00a0..0xffffff801feb10a0]
[ 0.682959] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G S 5.15.107 #0
[ 0.682966] Hardware name: Linksys E8450 (DT)
[ 0.682969] pstate: 800000c5 (Nzcv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 0.682975] pc : dequeue_entity+0x0/0x250
[ 0.682988] lr : dequeue_task_fair+0x98/0x290
[ 0.682992] sp : ffffffc008c48030
[ 0.682994] x29: ffffffc008c48030 x28: 0000000000000001 x27: ffffff801feb6380
[ 0.683004] x26: 0000000000000001 x25: ffffff801feb6300 x24: ffffff8000068000
[ 0.683011] x23: 0000000000000001 x22: 0000000000000009 x21: 0000000000000000
[ 0.683017] x20: ffffff801feb6380 x19: ffffff8000068080 x18: 0000000017a740a6
[ 0.683024] x17: ffffffc008bae748 x16: ffffffc008bae6d8 x15: ffffffffffffffff
[ 0.683031] x14: ffffffffffffffff x13: 0000000000000000 x12: 0000000f00000101
[ 0.683038] x11: 0000000000000449 x10: 0000000000000127 x9 : 0000000000000000
[ 0.683044] x8 : 0000000000000125 x7 : 0000000000116da1 x6 : 0000000000116da1
[ 0.683051] x5 : 00000000001165a1 x4 : ffffff801feb6e00 x3 : 0000000000000000
[ 0.683058] x2 : 0000000000000009 x1 : ffffff8000068080 x0 : ffffff801feb6380
[ 0.683066] Kernel panic - not syncing: kernel stack overflow
[ 0.683069] SMP: stopping secondary CPUs
[ 1.648361] SMP: failed to stop secondary CPUs 0-1
[ 1.648366] Kernel Offset: disabled
[ 1.648368] CPU features: 0x00003000,00000802
[ 1.648372] Memory Limit: none
Several factors contributed to this issue:
1. The mtk_bmt driver recursively calls its scan_bmt() helper function
during device initialization, while looking for a valid block
mapping table (BMT).
2. Commit fa4dc86e98 ("kernel: backport MEMREAD ioctl"):
- increased the size of some stack-allocated structures (like
struct mtd_oob_ops, used in bbt_nand_read(), which is indirectly
called from scan_bmt()),
- increased the stack size for some functions (for example,
spinand_mtd_read(), which is indirectly called from scan_bmt(),
now uses an extra stack-allocated struct mtd_ecc_stats).
3. OpenWrt currently compiles the kernel with the
-fno-optimize-sibling-calls flag, which prevents tail-call
optimization.
Collectively, all of these factors caused stack usage in the mtk_bmt
driver to grow excessively large, triggering stack overflows.
Recursion is not really necessary in scan_bmt() as it simply iterates
over flash memory blocks in reverse order, looking for a valid BMT.
Refactor the logic contained in the scan_bmt() and read_bmt() functions
in target/linux/generic/files/drivers/mtd/nand/mtk_bmt_v2.c so that deep
recursion is prevented (and therefore also any potential stack overflows
it may cause).
Link: https://lists.openwrt.org/pipermail/openwrt-devel/2023-April/040872.html
Signed-off-by: Michał Kępień <openwrt at kempniu.pl>
---
.../generic/files/drivers/mtd/nand/mtk_bmt_v2.c | 55 ++++++++++------------
1 file changed, 24 insertions(+), 31 deletions(-)
diff --git a/target/linux/generic/files/drivers/mtd/nand/mtk_bmt_v2.c b/target/linux/generic/files/drivers/mtd/nand/mtk_bmt_v2.c
index 2770376e98..6b06948c0f 100644
--- a/target/linux/generic/files/drivers/mtd/nand/mtk_bmt_v2.c
+++ b/target/linux/generic/files/drivers/mtd/nand/mtk_bmt_v2.c
@@ -191,36 +191,6 @@ static u16 get_bmt_index(struct bbmt *bmt)
return 0;
}
-static int
-read_bmt(u16 block, unsigned char *dat, unsigned char *fdm, int fdm_len)
-{
- u32 len = bmtd.bmt_pgs << bmtd.pg_shift;
-
- return bbt_nand_read(blk_pg(block), dat, len, fdm, fdm_len);
-}
-
-static struct bbbt *scan_bmt(u16 block)
-{
- u8 fdm[4];
-
- if (block < bmtd.pool_lba)
- return NULL;
-
- if (read_bmt(block, bmtd.bbt_buf, fdm, sizeof(fdm)))
- return scan_bmt(block - 1);
-
- if (is_valid_bmt(bmtd.bbt_buf, fdm)) {
- bmtd.bmt_blk_idx = get_bmt_index(bmt_tbl((struct bbbt *)bmtd.bbt_buf));
- if (bmtd.bmt_blk_idx == 0) {
- pr_info("[BBT] FATAL ERR: bmt block index is wrong!\n");
- return NULL;
- }
- pr_info("[BBT] BMT.v2 is found at 0x%x\n", block);
- return (struct bbbt *)bmtd.bbt_buf;
- } else
- return scan_bmt(block - 1);
-}
-
/* Write the Burner Bad Block Table to Nand Flash
* n - write BMT to bmt_tbl[n]
*/
@@ -472,7 +442,30 @@ static int mtk_bmt_init_v2(struct device_node *np)
/* Scanning start from the first page of the last block
* of whole flash
*/
- bmtd.bbt = scan_bmt(bmtd.total_blks - 1);
+ bmtd.bbt = NULL;
+ for (u16 block = bmtd.total_blks - 1; !bmtd.bbt && block >= bmtd.pool_lba; block--) {
+ u8 fdm[4];
+
+ if (bbt_nand_read(blk_pg(block), bmtd.bbt_buf, bufsz, fdm, sizeof(fdm))) {
+ /* Read failed, try the previous block */
+ continue;
+ }
+
+ if (!is_valid_bmt(bmtd.bbt_buf, fdm)) {
+ /* No valid BMT found, try the previous block */
+ continue;
+ }
+
+ bmtd.bmt_blk_idx = get_bmt_index(bmt_tbl((struct bbbt *)bmtd.bbt_buf));
+ if (bmtd.bmt_blk_idx == 0) {
+ pr_info("[BBT] FATAL ERR: bmt block index is wrong!\n");
+ break;
+ }
+
+ pr_info("[BBT] BMT.v2 is found at 0x%x\n", block);
+ bmtd.bbt = (struct bbbt *)bmtd.bbt_buf;
+ }
+
if (!bmtd.bbt) {
/* BMT not found */
if (bmtd.total_blks > BB_TABLE_MAX + BMT_TABLE_MAX) {
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