Commit 8c56c5db authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

mm: (un)track_pfn_copy() fix + doc improvements 

We got a late smatch warning and some additional review feedback.

	smatch warnings:
	mm/memory.c:1428 copy_page_range() error: uninitialized symbol 'pfn'.

We actually use the pfn only when it is properly initialized; however, we
may pass an uninitialized value to a function -- although it will not use
it that likely still is UB in C.

So let's just fix it by always initializing pfn in the caller of
track_pfn_copy(), and improving the documentation of track_pfn_copy().

While at it, clarify the doc of untrack_pfn_copy(), that internal checks
make sure if we actually have to untrack anything.

Link: https://lkml.kernel.org/r/20250408085950.976103-1-david@redhat.com


Fixes: dc84bc2a ("x86/mm/pat: Fix VM_PAT handling when fork() fails in copy_page_range()")
Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Reported-by: default avatarkernel test robot <lkp@intel.com>
Reported-by: default avatarDan Carpenter <error27@gmail.com>
Closes: https://lore.kernel.org/r/202503270941.IFILyNCX-lkp@intel.com/


Reviewed-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 8ab1b160

include/linux/pgtable.h

+6 −3
Original line number Diff line number Diff line
@@ -1511,8 +1511,9 @@ static inline void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot, 


/*

 * track_pfn_copy is called when a VM_PFNMAP VMA is about to get the page

 * tables copied during copy_page_range(). On success, stores the pfn to be

 * passed to untrack_pfn_copy().

 * tables copied during copy_page_range(). Will store the pfn to be

 * passed to untrack_pfn_copy() only if there is something to be untracked.

 * Callers should initialize the pfn to 0.

 */

static inline int track_pfn_copy(struct vm_area_struct *dst_vma,

		struct vm_area_struct *src_vma, unsigned long *pfn)
@@ -1522,7 +1523,9 @@ static inline int track_pfn_copy(struct vm_area_struct *dst_vma, 


/*

 * untrack_pfn_copy is called when a VM_PFNMAP VMA failed to copy during

 * copy_page_range(), but after track_pfn_copy() was already called.

 * copy_page_range(), but after track_pfn_copy() was already called. Can

 * be called even if track_pfn_copy() did not actually track anything:

 * handled internally.

 */

static inline void untrack_pfn_copy(struct vm_area_struct *dst_vma,

		unsigned long pfn)

mm/memory.c

+1 −1
Original line number Diff line number Diff line
@@ -1361,7 +1361,7 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) 
	struct mm_struct *dst_mm = dst_vma->vm_mm;

	struct mm_struct *src_mm = src_vma->vm_mm;

	struct mmu_notifier_range range;

	unsigned long next, pfn;

	unsigned long next, pfn = 0;

	bool is_cow;

	int ret;