[PATCH 2/2] mtd: spi-nor: take the flash lock in spi_nor_remove()

[Itai Handler <itai.handler@gmail.com>]

spi_nor_remove() restores the addressing mode with the same unlocked
call to spi_nor_restore() that spi_nor_shutdown() used before the
previous patch, and it is exposed the same way: the MTD device is still
registered at that point, so an unbind can run the restore while another
thread is in the middle of an operation. A busy flash silently ignores
the restore, and a restore that lands between two chunks of a read
switches the chip to 3-byte addressing while the driver keeps sending
4 address bytes.

Moving the restore after mtd_device_unregister() would not fix this.
Since commit 19bfa9ebebb5 ("mtd: use refcount to prevent corruption")
del_mtd_device() drops a reference instead of refusing with -EBUSY when
the device is in use, so unregistering returns right away and does not
wait for an operation that is already running.

Take nor->lock for the restore, as spi_nor_shutdown() now does. The
unregister stays unconditional, so a flash whose restore had to be
skipped is still torn down.

Fixes: 59b356ffd0b0 ("mtd: m25p80: restore the status of SPI flash when exiting")
Signed-off-by: Itai Handler <itai.handler@gmail.com>
---
 drivers/mtd/spi-nor/core.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 96dd6ae6d619..51128c94d1ce 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -3852,8 +3852,14 @@ static int spi_nor_probe(struct spi_mem *spimem)
 static int spi_nor_remove(struct spi_mem *spimem)
 {
 	struct spi_nor *nor = spi_mem_get_drvdata(spimem);
+	int ret;
 
-	spi_nor_restore(nor);
+	/* As in spi_nor_shutdown(), do not restore under an operation. */
+	ret = spi_nor_prep_and_lock(nor);
+	if (!ret) {
+		spi_nor_restore(nor);
+		spi_nor_unlock_and_unprep(nor);
+	}
 
 	/* Clean up MTD stuff. */
 	return mtd_device_unregister(&nor->mtd);