Messages in this thread Patch in this message | | | Subject | Re: WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f6f6e1a4), by kmemleak's scan_block() | From | Pekka Enberg <> | Date | Tue, 25 Aug 2009 12:26:55 +0300 |
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On Tue, 2009-08-25 at 10:21 +0100, Catalin Marinas wrote: > On Tue, 2009-08-25 at 12:11 +0300, Pekka Enberg wrote: > > On Tue, 2009-08-25 at 11:03 +0200, Vegard Nossum wrote: > > > I don't know so much about the kmemleak internals, but this I can say > > > about the kmemcheck part: According to your definition, an object is > > > initialized if all the bytes of an object are initialized. > > > > > > Is it possible that because of this, if we have a partially > > > uninitialized object, kmemleak will not record the pointers found in > > > that object? If so, it might skip valid pointers, and deem an object > > > unreferenced. Which could make kmemleak give false-positives. > > > > > > I think it would be better to ask kmemcheck on a per-pointer basis > > > (i.e. for each pointer-sized word in the object), whether it is > > > initialized or not. > > > > Yeah, makes sense. > > I think this patch should work. With a few minor (aesthetic) things > below and assuming that Ingo tests it (I don't have x86 hardware at hand > now):
Does this look OK to you?
>From 2ee25007d6bfe931ff2ae6c7e22a098578fb2dc5 Mon Sep 17 00:00:00 2001 From: Pekka Enberg <penberg@cs.helsinki.fi> Date: Tue, 25 Aug 2009 12:22:51 +0300 Subject: [PATCH] kmemleak: Don't scan uninitialized memory when kmemcheck is enabled
Ingo Molnar reported the following kmemcheck warning when running both kmemleak and kmemcheck enabled:
PM: Adding info for No Bus:vcsa7 WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f6f6e1a4) d873f9f600000000c42ae4c1005c87f70000000070665f666978656400000000 i i i i u u u u i i i i i i i i i i i i i i i i i i i i i u u u ^
Pid: 3091, comm: kmemleak Not tainted (2.6.31-rc7-tip #1303) P4DC6 EIP: 0060:[<c110301f>] EFLAGS: 00010006 CPU: 0 EIP is at scan_block+0x3f/0xe0 EAX: f40bd700 EBX: f40bd780 ECX: f16b46c0 EDX: 00000001 ESI: f6f6e1a4 EDI: 00000000 EBP: f10f3f4c ESP: c2605fcc DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 CR0: 8005003b CR2: e89a4844 CR3: 30ff1000 CR4: 000006f0 DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000 DR6: ffff4ff0 DR7: 00000400 [<c110313c>] scan_object+0x7c/0xf0 [<c1103389>] kmemleak_scan+0x1d9/0x400 [<c1103a3c>] kmemleak_scan_thread+0x4c/0xb0 [<c10819d4>] kthread+0x74/0x80 [<c10257db>] kernel_thread_helper+0x7/0x3c [<ffffffff>] 0xffffffff kmemleak: 515 new suspected memory leaks (see /sys/kernel/debug/kmemleak) kmemleak: 42 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
The problem here is that kmemleak will scan partially initialized objects that makes kmemcheck complain. Fix that up by skipping uninitialized memory regions when kmemcheck is enabled.
Reported-by: Ingo Molnar <mingo@elte.hu> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi> --- arch/x86/mm/kmemcheck/kmemcheck.c | 14 ++++++++++++++ include/linux/kmemcheck.h | 7 +++++++ mm/kmemleak.c | 12 ++++++++++-- 3 files changed, 31 insertions(+), 2 deletions(-)
diff --git a/arch/x86/mm/kmemcheck/kmemcheck.c b/arch/x86/mm/kmemcheck/kmemcheck.c index 2c55ed0..528bf95 100644 --- a/arch/x86/mm/kmemcheck/kmemcheck.c +++ b/arch/x86/mm/kmemcheck/kmemcheck.c @@ -331,6 +331,20 @@ static void kmemcheck_read_strict(struct pt_regs *regs, kmemcheck_shadow_set(shadow, size); } +bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size) +{ + enum kmemcheck_shadow status; + void *shadow; + + shadow = kmemcheck_shadow_lookup(addr); + if (!shadow) + return true; + + status = kmemcheck_shadow_test(shadow, size); + + return status == KMEMCHECK_SHADOW_INITIALIZED; +} + /* Access may cross page boundary */ static void kmemcheck_read(struct pt_regs *regs, unsigned long addr, unsigned int size) diff --git a/include/linux/kmemcheck.h b/include/linux/kmemcheck.h index 47b39b7..dc2fd54 100644 --- a/include/linux/kmemcheck.h +++ b/include/linux/kmemcheck.h @@ -34,6 +34,8 @@ void kmemcheck_mark_initialized_pages(struct page *p, unsigned int n); int kmemcheck_show_addr(unsigned long address); int kmemcheck_hide_addr(unsigned long address); +bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size); + #else #define kmemcheck_enabled 0 @@ -99,6 +101,11 @@ static inline void kmemcheck_mark_initialized_pages(struct page *p, { } +static inline bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size) +{ + return true; +} + #endif /* CONFIG_KMEMCHECK */ /* diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 6debe0d..e217c21 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -97,6 +97,7 @@ #include <asm/processor.h> #include <asm/atomic.h> +#include <linux/kmemcheck.h> #include <linux/kmemleak.h> /* @@ -884,15 +885,22 @@ static void scan_block(void *_start, void *_end, unsigned long *end = _end - (BYTES_PER_POINTER - 1); for (ptr = start; ptr < end; ptr++) { - unsigned long flags; - unsigned long pointer = *ptr; struct kmemleak_object *object; + unsigned long flags; + unsigned long pointer; if (allow_resched) cond_resched(); if (scan_should_stop()) break; + /* Don't scan uninitialized memory. */ + if (!kmemcheck_is_obj_initialized((unsigned long) ptr, + BYTES_PER_POINTER)) + continue; + + pointer = *ptr; + object = find_and_get_object(pointer, 1); if (!object) continue; -- 1.5.6.3
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