From 626c84340d54c07f46f6ae111ff4389980a86c64 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Micha=C5=82=20K=C4=99pie=C5=84?= Date: Sat, 29 Apr 2023 07:41:32 +0100 Subject: [PATCH] kernel: mtk_bmt: refactor to avoid deep recursion MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 --- .../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) { -- 2.30.2