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From: Christoph Hellwig <hch@infradead.org>
To: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, skhan@linuxfoundation.org,
	gregkh@linuxfoundation.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com,
	miquel.raynal@bootlin.com, richard@nod.at, vigneshr@ti.com,
	linux-mtd@lists.infradead.org
Subject: Re: [PATCH] block: break circular locks in blk_request_module
Date: Thu, 17 Jun 2021 12:51:23 +0100	[thread overview]
Message-ID: <YMs3O/cg4V7ywlVq@infradead.org> (raw)
In-Reply-To: <20210617092016.522985-1-desmondcheongzx@gmail.com>

On Thu, Jun 17, 2021 at 05:20:16PM +0800, Desmond Cheong Zhi Xi wrote:
>  	mutex_lock(&major_names_lock);
>  	for (n = &major_names[major_to_index(major)]; *n; n = &(*n)->next) {
>  		if ((*n)->major == major && (*n)->probe) {
> -			(*n)->probe(devt);
> +			probe = (*n)->probe;
>  			mutex_unlock(&major_names_lock);
> +			probe(devt);

And now you can all probe after it has been freed and/or the module has
been unloaded. The obviously correct fix is to only hold mtd_table_mutex
for the actually required critical section:

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index fb8e12d590a1..065d94f9b1fb 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -529,13 +529,11 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 		register_mtd_user(&blktrans_notifier);
 
 
-	mutex_lock(&mtd_table_mutex);
 
 	ret = register_blkdev(tr->major, tr->name);
 	if (ret < 0) {
 		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
 		       tr->name, tr->major, ret);
-		mutex_unlock(&mtd_table_mutex);
 		return ret;
 	}
 
@@ -545,12 +543,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	tr->blkshift = ffs(tr->blksize) - 1;
 
 	INIT_LIST_HEAD(&tr->devs);
-	list_add(&tr->list, &blktrans_majors);
 
+	mutex_lock(&mtd_table_mutex);
+	list_add(&tr->list, &blktrans_majors);
 	mtd_for_each_device(mtd)
 		if (mtd->type != MTD_ABSENT)
 			tr->add_mtd(tr, mtd);
-
 	mutex_unlock(&mtd_table_mutex);
 	return 0;
 }

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, skhan@linuxfoundation.org,
	gregkh@linuxfoundation.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com,
	miquel.raynal@bootlin.com, richard@nod.at, vigneshr@ti.com,
	linux-mtd@lists.infradead.org
Subject: Re: [PATCH] block: break circular locks in blk_request_module
Date: Thu, 17 Jun 2021 12:51:23 +0100	[thread overview]
Message-ID: <YMs3O/cg4V7ywlVq@infradead.org> (raw)
In-Reply-To: <20210617092016.522985-1-desmondcheongzx@gmail.com>

On Thu, Jun 17, 2021 at 05:20:16PM +0800, Desmond Cheong Zhi Xi wrote:
>  	mutex_lock(&major_names_lock);
>  	for (n = &major_names[major_to_index(major)]; *n; n = &(*n)->next) {
>  		if ((*n)->major == major && (*n)->probe) {
> -			(*n)->probe(devt);
> +			probe = (*n)->probe;
>  			mutex_unlock(&major_names_lock);
> +			probe(devt);

And now you can all probe after it has been freed and/or the module has
been unloaded. The obviously correct fix is to only hold mtd_table_mutex
for the actually required critical section:

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index fb8e12d590a1..065d94f9b1fb 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -529,13 +529,11 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 		register_mtd_user(&blktrans_notifier);
 
 
-	mutex_lock(&mtd_table_mutex);
 
 	ret = register_blkdev(tr->major, tr->name);
 	if (ret < 0) {
 		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
 		       tr->name, tr->major, ret);
-		mutex_unlock(&mtd_table_mutex);
 		return ret;
 	}
 
@@ -545,12 +543,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	tr->blkshift = ffs(tr->blksize) - 1;
 
 	INIT_LIST_HEAD(&tr->devs);
-	list_add(&tr->list, &blktrans_majors);
 
+	mutex_lock(&mtd_table_mutex);
+	list_add(&tr->list, &blktrans_majors);
 	mtd_for_each_device(mtd)
 		if (mtd->type != MTD_ABSENT)
 			tr->add_mtd(tr, mtd);
-
 	mutex_unlock(&mtd_table_mutex);
 	return 0;
 }

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Cc: axboe@kernel.dk,
	syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com,
	vigneshr@ti.com, miquel.raynal@bootlin.com,
	linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
	richard@nod.at, linux-mtd@lists.infradead.org,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [PATCH] block: break circular locks in blk_request_module
Date: Thu, 17 Jun 2021 12:51:23 +0100	[thread overview]
Message-ID: <YMs3O/cg4V7ywlVq@infradead.org> (raw)
In-Reply-To: <20210617092016.522985-1-desmondcheongzx@gmail.com>

On Thu, Jun 17, 2021 at 05:20:16PM +0800, Desmond Cheong Zhi Xi wrote:
>  	mutex_lock(&major_names_lock);
>  	for (n = &major_names[major_to_index(major)]; *n; n = &(*n)->next) {
>  		if ((*n)->major == major && (*n)->probe) {
> -			(*n)->probe(devt);
> +			probe = (*n)->probe;
>  			mutex_unlock(&major_names_lock);
> +			probe(devt);

And now you can all probe after it has been freed and/or the module has
been unloaded. The obviously correct fix is to only hold mtd_table_mutex
for the actually required critical section:

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index fb8e12d590a1..065d94f9b1fb 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -529,13 +529,11 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 		register_mtd_user(&blktrans_notifier);
 
 
-	mutex_lock(&mtd_table_mutex);
 
 	ret = register_blkdev(tr->major, tr->name);
 	if (ret < 0) {
 		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
 		       tr->name, tr->major, ret);
-		mutex_unlock(&mtd_table_mutex);
 		return ret;
 	}
 
@@ -545,12 +543,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	tr->blkshift = ffs(tr->blksize) - 1;
 
 	INIT_LIST_HEAD(&tr->devs);
-	list_add(&tr->list, &blktrans_majors);
 
+	mutex_lock(&mtd_table_mutex);
+	list_add(&tr->list, &blktrans_majors);
 	mtd_for_each_device(mtd)
 		if (mtd->type != MTD_ABSENT)
 			tr->add_mtd(tr, mtd);
-
 	mutex_unlock(&mtd_table_mutex);
 	return 0;
 }
_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

  reply	other threads:[~2021-06-17 11:52 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-17  9:20 [PATCH] block: break circular locks in blk_request_module Desmond Cheong Zhi Xi
2021-06-17  9:20 ` Desmond Cheong Zhi Xi
2021-06-17 11:51 ` Christoph Hellwig [this message]
2021-06-17 11:51   ` Christoph Hellwig
2021-06-17 11:51   ` Christoph Hellwig
2021-06-17 15:23   ` Desmond Cheong Zhi Xi
2021-06-17 15:23     ` Desmond Cheong Zhi Xi
2021-06-17 15:23     ` Desmond Cheong Zhi Xi
2021-06-17 15:27     ` Christoph Hellwig
2021-06-17 15:27       ` Christoph Hellwig
2021-06-17 15:27       ` Christoph Hellwig

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