2018-08-13 13:38:03

by Christophe Leroy

Subject: [PATCH] powerpc/mm: Don't report hugepage tables as memory leaks when using kmemleak

When a process allocates a hugepage, the following leak is
reported by kmemleak. This is a false positive which is
due to the pointer to the table being stored in the PGD
as physical memory address and not virtual memory pointer.

unreferenced object 0xc30f8200 (size 512):
comm "mmap", pid 374, jiffies 4872494 (age 627.630s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<e32b68da>] huge_pte_alloc+0xdc/0x1f8
[<9e0df1e1>] hugetlb_fault+0x560/0x8f8
[<7938ec6c>] follow_hugetlb_page+0x14c/0x44c
[<afbdb405>] __get_user_pages+0x1c4/0x3dc
[<b8fd7cd9>] __mm_populate+0xac/0x140
[<3215421e>] vm_mmap_pgoff+0xb4/0xb8
[<c148db69>] ksys_mmap_pgoff+0xcc/0x1fc
[<4fcd760f>] ret_from_syscall+0x0/0x38

See commit a984506c542e2 ("powerpc/mm: Don't report PUDs as
memory leaks when using kmemleak") for detailed explanation.

To fix that, this patch tells kmemleak to ignore the allocated
hugepage table.

Signed-off-by: Christophe Leroy <[email protected]>
---
arch/powerpc/mm/hugetlbpage.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index e87f9ef9115b..7296a42eb62e 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -19,6 +19,7 @@
#include <linux/moduleparam.h>
#include <linux/swap.h>
#include <linux/swapops.h>
+#include <linux/kmemleak.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
#include <asm/tlb.h>
@@ -112,6 +113,8 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
for (i = i - 1 ; i >= 0; i--, hpdp--)
*hpdp = __hugepd(0);
kmem_cache_free(cachep, new);
+ } else {
+ kmemleak_ignore(new);
}
spin_unlock(ptl);
return 0;
--
2.13.3

2018-10-04 06:16:32

by Michael Ellerman

Subject: Re: powerpc/mm: Don't report hugepage tables as memory leaks when using kmemleak

On Mon, 2018-08-13 at 13:19:52 UTC, Christophe Leroy wrote:
> When a process allocates a hugepage, the following leak is
> reported by kmemleak. This is a false positive which is
> due to the pointer to the table being stored in the PGD
> as physical memory address and not virtual memory pointer.
>
> unreferenced object 0xc30f8200 (size 512):
> comm "mmap", pid 374, jiffies 4872494 (age 627.630s)
> hex dump (first 32 bytes):
> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> backtrace:
> [<e32b68da>] huge_pte_alloc+0xdc/0x1f8
> [<9e0df1e1>] hugetlb_fault+0x560/0x8f8
> [<7938ec6c>] follow_hugetlb_page+0x14c/0x44c
> [<afbdb405>] __get_user_pages+0x1c4/0x3dc
> [<b8fd7cd9>] __mm_populate+0xac/0x140
> [<3215421e>] vm_mmap_pgoff+0xb4/0xb8
> [<c148db69>] ksys_mmap_pgoff+0xcc/0x1fc
> [<4fcd760f>] ret_from_syscall+0x0/0x38
>
> See commit a984506c542e2 ("powerpc/mm: Don't report PUDs as
> memory leaks when using kmemleak") for detailed explanation.
>
> To fix that, this patch tells kmemleak to ignore the allocated
> hugepage table.
>
> Signed-off-by: Christophe Leroy <[email protected]>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/803d690e68f0c5230183f1a42c7d50

cheers