[PATCH] fs: Fix default mount when device already mounted

[PATCH] fs: Fix default mount when device already mounted

[Stefan Riedmueller]

Let cdev_mount_default return an error in case the device is already
mounted to a different location than the default mount point.

Otherwise the automount routine can get stuck in an infinite loop
spamming:

mounted /dev/mmc0.0 on /mnt/mmc
mounted /dev/mmc0.0 on /mnt/mmc
mounted /dev/mmc0.0 on /mnt/mmc

Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
---
 fs/fs.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/fs/fs.c b/fs/fs.c
index 3db24b7b6822..4f2345d22544 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -951,9 +951,10 @@ const char *cdev_get_mount_path(struct cdev *cdev)
 /*
  * cdev_mount_default - mount a cdev to the default path
  *
- * If a cdev is already mounted return the path it's mounted on, otherwise
- * mount it to /mnt/<cdevname> and return the path. Returns an error pointer
- * on failure.
+ * If a cdev is already mounted to the default mount path return the path
+ * it's mounted on. If it is mounted to any other path return EBUSY.
+ * Otherwise mount it to /mnt/<cdevname> and return the path. Returns an
+ * error pointer on failure.
  */
 const char *cdev_mount_default(struct cdev *cdev, const char *fsoptions)
 {
@@ -962,15 +963,24 @@ const char *cdev_mount_default(struct cdev *cdev, const char *fsoptions)
 	int ret;
 
 	/*
-	 * If this cdev is already mounted somewhere use this path
-	 * instead of mounting it again to avoid corruption on the
-	 * filesystem. Note this ignores eventual fsoptions though.
+	 * If this cdev is already mounted somewhere other than the
+	 * default mount path return -EBUSY instead of mounting it
+	 * again to avoid corruption on the filesystem. Note this
+	 * ignores eventual fsoptions though. If the cdev is already
+	 * mounted on the default path just return that path.
 	 */
 	path = cdev_get_mount_path(cdev);
-	if (path)
-		return path;
-
 	newpath = basprintf("/mnt/%s", cdev->name);
+
+	if (path) {
+		if (strcmp(newpath, path)) {
+			free(newpath);
+			return ERR_PTR(-EBUSY);
+		} else {
+			return path;
+		}
+	}
+
 	make_directory(newpath);
 
 	devpath = basprintf("/dev/%s", cdev->name);
-- 
2.25.1


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Re: [PATCH] fs: Fix default mount when device already mounted

[Sascha Hauer]

Hi Stefan,

On Tue, Mar 16, 2021 at 01:35:46PM +0100, Stefan Riedmueller wrote:
> Let cdev_mount_default return an error in case the device is already
> mounted to a different location than the default mount point.
> 
> Otherwise the automount routine can get stuck in an infinite loop
> spamming:
> 
> mounted /dev/mmc0.0 on /mnt/mmc
> mounted /dev/mmc0.0 on /mnt/mmc
> mounted /dev/mmc0.0 on /mnt/mmc
> 
> Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
> ---
>  fs/fs.c | 28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/fs.c b/fs/fs.c
> index 3db24b7b6822..4f2345d22544 100644
> --- a/fs/fs.c
> +++ b/fs/fs.c
> @@ -951,9 +951,10 @@ const char *cdev_get_mount_path(struct cdev *cdev)
>  /*
>   * cdev_mount_default - mount a cdev to the default path
>   *
> - * If a cdev is already mounted return the path it's mounted on, otherwise
> - * mount it to /mnt/<cdevname> and return the path. Returns an error pointer
> - * on failure.
> + * If a cdev is already mounted to the default mount path return the path
> + * it's mounted on. If it is mounted to any other path return EBUSY.
> + * Otherwise mount it to /mnt/<cdevname> and return the path. Returns an
> + * error pointer on failure.

blspec depends on the return-current-path-when-mounted part you are
removing here. I added the following patch before applying this one.

Sascha

------------------------------8<-------------------------------

>From 7dc73d3618a15f0d858d5409574f38f9f83905ef Mon Sep 17 00:00:00 2001
From: Sascha Hauer <s.hauer@pengutronix.de>
Date: Wed, 17 Mar 2021 10:25:47 +0100
Subject: [PATCH] blspec: Check if already mounted before mounting

cdev_mount_default() either mounts a cdev and returns the path it's
mounted to or directly returns the path when it already is mounted.
This will change in the next patch: When the cdev is already mounted
cdev_mount_default() will return -EBUSY instead. To let blspec
work when a cdev is already mounted check for the actual mount path
before trying to mount it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 common/blspec.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/common/blspec.c b/common/blspec.c
index c05d8a8297..ad80d7a8cd 100644
--- a/common/blspec.c
+++ b/common/blspec.c
@@ -729,7 +729,9 @@ static int blspec_scan_cdev(struct bootentries *bootentries, struct cdev *cdev)
 			found += ret;
 	}
 
-	rootpath = cdev_mount_default(cdev, NULL);
+	rootpath = cdev_get_mount_path(cdev);
+	if (!rootpath)
+		rootpath = cdev_mount_default(cdev, NULL);
 	if (!IS_ERR(rootpath)) {
 		ret = blspec_scan_directory(bootentries, rootpath);
 		if (ret > 0)
-- 
2.29.2


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