[PATCH RFC] mtd: rawnand: xway: don't yield while holding spinlock
tom at tomn.co.uk
Sun Mar 26 16:52:39 PDT 2023
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.
Signed-off-by: Thomas Nixon <tom at 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
@@ -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)
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