[PATCH] init: do_mounts: use kmalloc() for allocations of temporary buffers

[PATCH] init: do_mounts: use kmalloc() for allocations of temporary buffers

[Mike Rapoport (Microsoft)]

Several places in init/do_mounts.c allocate temporary buffers for
filesystem names or options using __get_free_page() or alloc_page().

Usage of alloc_page() APIs is not required there and only creates
unnecessary noise with castings or conversion from struct page to void *.

kmalloc() is a better API for these uses and it also provides better
scalability and more debugging possibilities.

Replace use of __get_free_page() and alloc_page() with kmalloc().

While on it, add a check for -ENOMEM condition in mount_root_generic().

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
This is a (tiny) part of larger work of replacing page allocator calls
with kmalloc:

Also in git:
https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git gfp-to-kmalloc/init
---
 init/do_mounts.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 55ed3ac0b70f..95e0b3a0f711 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -143,16 +143,14 @@ static int __init do_mount_root(const char *name, const char *fs,
 				 const int flags, const void *data)
 {
 	struct super_block *s;
-	struct page *p = NULL;
 	char *data_page = NULL;
 	int ret;
 
 	if (data) {
 		/* init_mount() requires a full page as fifth argument */
-		p = alloc_page(GFP_KERNEL);
-		if (!p)
+		data_page = kmalloc(PAGE_SIZE, GFP_KERNEL);
+		if (!data_page)
 			return -ENOMEM;
-		data_page = page_address(p);
 		strscpy_pad(data_page, data, PAGE_SIZE);
 	}
 
@@ -170,19 +168,20 @@ static int __init do_mount_root(const char *name, const char *fs,
 	       MAJOR(ROOT_DEV), MINOR(ROOT_DEV));
 
 out:
-	if (p)
-		put_page(p);
+	kfree(data_page);
 	return ret;
 }
 
 void __init mount_root_generic(char *name, char *pretty_name, int flags)
 {
-	struct page *page = alloc_page(GFP_KERNEL);
-	char *fs_names = page_address(page);
+	char *fs_names = kmalloc(PAGE_SIZE, GFP_KERNEL);
 	char *p;
 	char b[BDEVNAME_SIZE];
 	int num_fs, i;
 
+	if (!fs_names)
+		panic("VFS: Unable to mount root fs: not enough memory");
+
 	scnprintf(b, BDEVNAME_SIZE, "unknown-block(%u,%u)",
 		  MAJOR(ROOT_DEV), MINOR(ROOT_DEV));
 	if (root_fs_names)
@@ -242,7 +241,7 @@ void __init mount_root_generic(char *name, char *pretty_name, int flags)
 	printk("\n");
 	panic("VFS: Unable to mount root fs on \"%s\" or %s", pretty_name, b);
 out:
-	put_page(page);
+	kfree(fs_names);
 }
  
 #ifdef CONFIG_ROOT_NFS
@@ -343,7 +342,7 @@ static int __init mount_nodev_root(char *root_device_name)
 	int err = -EINVAL;
 	int num_fs, i;
 
-	fs_names = (void *)__get_free_page(GFP_KERNEL);
+	fs_names = kmalloc(PAGE_SIZE, GFP_KERNEL);
 	if (!fs_names)
 		return -EINVAL;
 	num_fs = split_fs_names(fs_names, PAGE_SIZE);
@@ -360,7 +359,7 @@ static int __init mount_nodev_root(char *root_device_name)
 			break;
 	}
 
-	free_page((unsigned long)fs_names);
+	kfree(fs_names);
 	return err;
 }
 

---
base-commit: 5d6919055dec134de3c40167a490f33c74c12581
change-id: 20260520-init-152a94946e25

Best regards,
--  
Sincerely yours,
Mike.

Re: [PATCH] init: do_mounts: use kmalloc() for allocations of temporary buffers

[David Disseldorp]

On Wed, 20 May 2026 11:16:51 +0300, Mike Rapoport (Microsoft) wrote:

> Several places in init/do_mounts.c allocate temporary buffers for
> filesystem names or options using __get_free_page() or alloc_page().
> 
> Usage of alloc_page() APIs is not required there and only creates
> unnecessary noise with castings or conversion from struct page to void *.
> 
> kmalloc() is a better API for these uses and it also provides better
> scalability and more debugging possibilities.
> 
> Replace use of __get_free_page() and alloc_page() with kmalloc().
> 
> While on it, add a check for -ENOMEM condition in mount_root_generic().
> 
> Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Looks fine...
Reviewed-by: David Disseldorp <ddiss@suse.de>

Re: [PATCH] init: do_mounts: use kmalloc() for allocations of temporary buffers

[kernel test robot]

Hi Mike,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 5d6919055dec134de3c40167a490f33c74c12581]

url:    https://github.com/intel-lab-lkp/linux/commits/Mike-Rapoport-Microsoft/init-do_mounts-use-kmalloc-for-allocations-of-temporary-buffers/20260520-164927
base:   5d6919055dec134de3c40167a490f33c74c12581
patch link:    https://lore.kernel.org/r/20260520-init-v1-1-aaf2ebac5ad9%40kernel.org
patch subject: [PATCH] init: do_mounts: use kmalloc() for allocations of temporary buffers
config: xtensa-allnoconfig (https://download.01.org/0day-ci/archive/20260520/202605202055.kwkCHqR9-lkp@intel.com/config)
compiler: xtensa-linux-gcc (GCC) 15.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260520/202605202055.kwkCHqR9-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202605202055.kwkCHqR9-lkp@intel.com/

All warnings (new ones prefixed by >>, old ones prefixed by <<):

>> WARNING: modpost: vmlinux: section mismatch in reference: try_to_run_init_process+0x24 (section: .text.unlikely) -> initcall_level_names (section: .init.data)

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki