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From:   Sean Nyekjaer <sean@geanix.com>
To:     Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Boris Brezillon <bbrezillon@kernel.org>
Cc:     Sean Nyekjaer <sean@geanix.com>, linux-mtd@lists.infradead.org,
        linux-kernel@vger.kernel.org
Subject: [RFC PATCH] mtd: rawnand: use mutex to protect access while in suspend
Date:   Mon,  4 Oct 2021 08:56:09 +0200
Message-Id: <20211004065608.3190348-1-sean@geanix.com>
MIME-Version: 1.0
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This will prevent nand_get_device() from returning -EBUSY.
It will force mtd_write()/mtd_read() to wait for the nand_resume() to unlock
access to the mtd device.

Then we avoid -EBUSY is returned to ubifsi via mtd_write()/mtd_read(),
that will in turn hard error on every error returened.
We have seen during ubifs tries to call mtd_write before the mtd device
is resumed.

Exec_op[0] speed things up, so we see this race when the device is
resuming. But it's actually "mtd: rawnand: Simplify the locking" that
allows it to return -EBUSY, before that commit it would have waited for
the mtd device to resume.

Tested on a iMX6ULL.

[0]:
ef347c0cfd61 ("mtd: rawnand: gpmi: Implement exec_op")

Fixes: 013e6292aaf5 ("mtd: rawnand: Simplify the locking")
Signed-off-by: Sean Nyekjaer <sean@geanix.com>
---

I did this a RFC as we probably will need to remove the suspended
variable as it's kinda made obsolute by this change.
Should we introduce a new mutex? Or maybe a spin_lock?

 drivers/mtd/nand/raw/nand_base.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
index 3d6c6e880520..0ea343404cac 100644
--- a/drivers/mtd/nand/raw/nand_base.c
+++ b/drivers/mtd/nand/raw/nand_base.c
@@ -4567,7 +4567,6 @@ static int nand_suspend(struct mtd_info *mtd)
 		ret = chip->ops.suspend(chip);
 	if (!ret)
 		chip->suspended = 1;
-	mutex_unlock(&chip->lock);
 
 	return ret;
 }
@@ -4580,7 +4579,6 @@ static void nand_resume(struct mtd_info *mtd)
 {
 	struct nand_chip *chip = mtd_to_nand(mtd);
 
-	mutex_lock(&chip->lock);
 	if (chip->suspended) {
 		if (chip->ops.resume)
 			chip->ops.resume(chip);
-- 
2.33.0