From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from b.ns.miles-group.at ([95.130.255.144] helo=radon.swed.at) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1bJhc6-0005Em-KU for linux-mtd@lists.infradead.org; Sun, 03 Jul 2016 13:39:11 +0000 To: "linux-mtd@lists.infradead.org" Cc: Boris Brezillon , Brian Norris From: Richard Weinberger Subject: Race-free NAND device removal Message-ID: <57791562.2020703@nod.at> Date: Sun, 3 Jul 2016 15:38:42 +0200 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hi! While working on nandsim I realized that nand_release() ignores the return value from mtd_device_unregister(). That means NAND devices cannot removed in a race-free manner. Consider a NAND driver that registers ->_get_device() and ->_put_device() callbacks for refcounting. In its removal function it will return -EBUSY whenever the refcount is > 0. But when device is claimed while removing it, it can happen that the refcount increments after the check. MTD can deal with that and mtd_device_unregister() will return EBUSY. But nand_release() won't notice and the NAND driver continues with the tear down process. Would be a change like the following one acceptable or is a NAND driver allowed to call mtd_device_unregister() itself? AFAICT the additional call to mtd_device_unregister() in nand_release() would be an nop then. diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c index 0b0dc29..dc76bc6 100644 --- a/drivers/mtd/nand/nand_base.c +++ b/drivers/mtd/nand/nand_base.c @@ -4604,16 +4604,19 @@ EXPORT_SYMBOL(nand_scan); * nand_release - [NAND Interface] Free resources held by the NAND device * @mtd: MTD device structure */ -void nand_release(struct mtd_info *mtd) +int nand_release(struct mtd_info *mtd) { + int ret; struct nand_chip *chip = mtd_to_nand(mtd); + ret = mtd_device_unregister(mtd); + if (ret) + return ret; + if (chip->ecc.mode == NAND_ECC_SOFT && chip->ecc.algo == NAND_ECC_BCH) nand_bch_free((struct nand_bch_control *)chip->ecc.priv); - mtd_device_unregister(mtd); - /* Free bad block table memory */ kfree(chip->bbt); if (!(chip->options & NAND_OWN_BUFFERS)) @@ -4623,6 +4626,8 @@ void nand_release(struct mtd_info *mtd) if (chip->badblock_pattern && chip->badblock_pattern->options & NAND_BBT_DYNAMICSTRUCT) kfree(chip->badblock_pattern); + + return 0; } EXPORT_SYMBOL_GPL(nand_release); diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h index fbe8e16..c15b1c4 100644 --- a/include/linux/mtd/nand.h +++ b/include/linux/mtd/nand.h @@ -39,7 +39,7 @@ extern int nand_scan_ident(struct mtd_info *mtd, int max_chips, extern int nand_scan_tail(struct mtd_info *mtd); /* Free resources held by the NAND device */ -extern void nand_release(struct mtd_info *mtd); +extern int nand_release(struct mtd_info *mtd); /* Internal helper for board drivers which need to override command function */ extern void nand_wait_ready(struct mtd_info *mtd); Thanks, //richard