From: Thomas Nixon <tom@tomn.co.uk>
To: linux-mtd@lists.infradead.org
Subject: [PATCH RFC] mtd: rawnand: xway: don't yield while holding spinlock
Date: Mon, 27 Mar 2023 00:52:39 +0100 [thread overview]
Message-ID: <ZCDax6AWvz9mKGPr@tom-tp> (raw)
xway_nand holds the ebu_lock spinlock during transactions by locking and
unlocking in select_chip. Yielding while this is held is bad, so block
in dev_ready so that nand_wait and nand_wait_ready never yield.
This fixes crashes mostly seen in ath9k_pci_owl_loader.
Tested on a bt homehub v5a, with openwrt-patched 5.10 and 5.15 kernels.
Link: https://github.com/openwrt/openwrt/issues/9829
Signed-off-by: Thomas Nixon <tom@tomn.co.uk>
---
Obviously this is a hack, but other options don't seem great either --
maybe someone has a better idea?
Perhaps this should implement a timeout warning too? Adding an actual
timeout seems tricky, as xway_dev_ready would have to return 1 even when
it's not ready in to break out of the loop in nand_wait/nand_wait_ready
without yielding (and triggering this bug).
drivers/mtd/nand/raw/xway_nand.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/mtd/nand/raw/xway_nand.c b/drivers/mtd/nand/raw/xway_nand.c
index 035b82aa2f4a..ea10a35db6db 100644
--- a/drivers/mtd/nand/raw/xway_nand.c
+++ b/drivers/mtd/nand/raw/xway_nand.c
@@ -122,7 +122,13 @@ static void xway_cmd_ctrl(struct nand_chip *chip, int cmd, unsigned int ctrl)
static int xway_dev_ready(struct nand_chip *chip)
{
- return ltq_ebu_r32(EBU_NAND_WAIT) & NAND_WAIT_RD;
+ /*
+ * wait until ready, as otherwise the driver will yield in nand_wait or
+ * nand_wait_ready, which is a bad idea when we're holding ebu_lock
+ */
+ while ((ltq_ebu_r32(EBU_NAND_WAIT) & NAND_WAIT_RD) == 0)
+ ;
+ return 1;
}
static unsigned char xway_read_byte(struct nand_chip *chip)
--
2.33.1
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