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Groups > linux.kernel > #1499453 > unrolled thread

[PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning

Started byCatalin Marinas <catalin.marinas@arm.com>
First post2016-10-12 12:00 +0200
Last post2016-10-12 18:40 +0200
Articles 6 — 4 participants

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  [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning Catalin Marinas <catalin.marinas@arm.com> - 2016-10-12 12:00 +0200
    Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2016-10-12 12:30 +0200
      Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed  during scanning Catalin Marinas <catalin.marinas@arm.com> - 2016-10-12 12:50 +0200
    Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed  during scanning Michal Hocko <mhocko@kernel.org> - 2016-10-12 12:50 +0200
    Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed  during scanning Catalin Marinas <catalin.marinas@arm.com> - 2016-10-12 18:20 +0200
    Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed  during scanning CAI Qian <caiqian@redhat.com> - 2016-10-12 18:40 +0200

#1499453 — [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning

FromCatalin Marinas <catalin.marinas@arm.com>
Date2016-10-12 12:00 +0200
Subject[PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning
Message-ID<sroum-2vS-11@gated-at.bofh.it>
Commit 68f24b08ee89 ("sched/core: Free the stack early if
CONFIG_THREAD_INFO_IN_TASK") may cause the task->stack to be freed
during kmemleak_scan() execution, leading to either a NULL pointer
fault (if task->stack is NULL) or kmemleak accessing already freed
memory. This patch uses the new try_get_task_stack() API to ensure that
the task stack is not freed during kmemleak stack scanning.

Fixes: 68f24b08ee89 ("sched/core: Free the stack early if CONFIG_THREAD_INFO_IN_TASK")
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: CAI Qian <caiqian@redhat.com>
Reported-by: CAI Qian <caiqian@redhat.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---

This was reported in a subsequent comment here:

https://bugzilla.kernel.org/show_bug.cgi?id=173901

However, the original bugzilla entry doesn't look related to task stack
freeing as it was first reported on 4.8-rc8. Andy, sorry for cc'ing you
to bugzilla, please feel free to remove your email from the bug above (I
can't seem to be able to do it).

 mm/kmemleak.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index a5e453cf05c4..e5355a5b423f 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1453,8 +1453,11 @@ static void kmemleak_scan(void)
 
 		read_lock(&tasklist_lock);
 		do_each_thread(g, p) {
-			scan_block(task_stack_page(p), task_stack_page(p) +
-				   THREAD_SIZE, NULL);
+			void *stack = try_get_task_stack(p);
+			if (stack) {
+				scan_block(stack, stack + THREAD_SIZE, NULL);
+				put_task_stack(p);
+			}
 		} while_each_thread(g, p);
 		read_unlock(&tasklist_lock);
 	}

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#1499467

From"Hillf Danton" <hillf.zj@alibaba-inc.com>
Date2016-10-12 12:30 +0200
Message-ID<sroXo-372-7@gated-at.bofh.it>
In reply to#1499453
> @@ -1453,8 +1453,11 @@ static void kmemleak_scan(void)
> 
>  		read_lock(&tasklist_lock);
>  		do_each_thread(g, p) {

Take a look at this commit please.
	1da4db0cd5 ("oom_kill: change oom_kill.c to use for_each_thread()")

> -			scan_block(task_stack_page(p), task_stack_page(p) +
> -				   THREAD_SIZE, NULL);
> +			void *stack = try_get_task_stack(p);
> +			if (stack) {
> +				scan_block(stack, stack + THREAD_SIZE, NULL);
> +				put_task_stack(p);
> +			}
>  		} while_each_thread(g, p);
>  		read_unlock(&tasklist_lock);
>  	}
>

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#1499478 — Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning

FromCatalin Marinas <catalin.marinas@arm.com>
Date2016-10-12 12:50 +0200
SubjectRe: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning
Message-ID<srpgJ-3eb-7@gated-at.bofh.it>
In reply to#1499467
On Wed, Oct 12, 2016 at 06:16:46PM +0800, Hillf Danton wrote:
> > @@ -1453,8 +1453,11 @@ static void kmemleak_scan(void)
> > 
> >  		read_lock(&tasklist_lock);
> >  		do_each_thread(g, p) {
> 
> Take a look at this commit please.
> 	1da4db0cd5 ("oom_kill: change oom_kill.c to use for_each_thread()")

Thanks. Isn't holding tasklist_lock here enough to avoid such races?

-- 
Catalin

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#1499480 — Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning

FromMichal Hocko <mhocko@kernel.org>
Date2016-10-12 12:50 +0200
SubjectRe: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning
Message-ID<srpgJ-3eb-9@gated-at.bofh.it>
In reply to#1499453
On Wed 12-10-16 10:57:03, Catalin Marinas wrote:
> Commit 68f24b08ee89 ("sched/core: Free the stack early if
> CONFIG_THREAD_INFO_IN_TASK") may cause the task->stack to be freed
> during kmemleak_scan() execution, leading to either a NULL pointer
> fault (if task->stack is NULL) or kmemleak accessing already freed
> memory. This patch uses the new try_get_task_stack() API to ensure that
> the task stack is not freed during kmemleak stack scanning.

Looks good to me
 
> Fixes: 68f24b08ee89 ("sched/core: Free the stack early if CONFIG_THREAD_INFO_IN_TASK")
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: CAI Qian <caiqian@redhat.com>
> Reported-by: CAI Qian <caiqian@redhat.com>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> 
> This was reported in a subsequent comment here:
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=173901
> 
> However, the original bugzilla entry doesn't look related to task stack
> freeing as it was first reported on 4.8-rc8. Andy, sorry for cc'ing you
> to bugzilla, please feel free to remove your email from the bug above (I
> can't seem to be able to do it).
> 
>  mm/kmemleak.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index a5e453cf05c4..e5355a5b423f 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -1453,8 +1453,11 @@ static void kmemleak_scan(void)
>  
>  		read_lock(&tasklist_lock);
>  		do_each_thread(g, p) {
> -			scan_block(task_stack_page(p), task_stack_page(p) +
> -				   THREAD_SIZE, NULL);
> +			void *stack = try_get_task_stack(p);
> +			if (stack) {
> +				scan_block(stack, stack + THREAD_SIZE, NULL);
> +				put_task_stack(p);
> +			}
>  		} while_each_thread(g, p);
>  		read_unlock(&tasklist_lock);
>  	}
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

-- 
Michal Hocko
SUSE Labs

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#1499802 — Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning

FromCatalin Marinas <catalin.marinas@arm.com>
Date2016-10-12 18:20 +0200
SubjectRe: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning
Message-ID<sruq5-6PD-15@gated-at.bofh.it>
In reply to#1499453
On Wed, Oct 12, 2016 at 11:54:17AM -0400, CAI Qian wrote:
> ----- Original Message -----
> > From: "Catalin Marinas" <catalin.marinas@arm.com>
> > To: linux-mm@kvack.org
> > Cc: linux-kernel@vger.kernel.org, "Andrew Morton" <akpm@linux-foundation.org>, "Andy Lutomirski" <luto@kernel.org>,
> > "CAI Qian" <caiqian@redhat.com>
> > Sent: Wednesday, October 12, 2016 5:57:03 AM
> > Subject: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning
> > 
> > Commit 68f24b08ee89 ("sched/core: Free the stack early if
> > CONFIG_THREAD_INFO_IN_TASK") may cause the task->stack to be freed
> > during kmemleak_scan() execution, leading to either a NULL pointer
> > fault (if task->stack is NULL) or kmemleak accessing already freed
> > memory. This patch uses the new try_get_task_stack() API to ensure that
> > the task stack is not freed during kmemleak stack scanning.
> > 
> > Fixes: 68f24b08ee89 ("sched/core: Free the stack early if
> > CONFIG_THREAD_INFO_IN_TASK")
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Andy Lutomirski <luto@kernel.org>
> > Cc: CAI Qian <caiqian@redhat.com>
> > Reported-by: CAI Qian <caiqian@redhat.com>
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> 
> Tested-by: CAI Qian <caiqian@redhat.com>

Thanks.

BTW, I noticed a few false positives reported by kmemleak with the
CONFIG_VMAP_STACK enabled caused by the fact that kmemleak requires two
references (instead of one) to a vmalloc'ed object because of the
vm_struct already containing the address. The cached_stack[] array only
stores the vm_struct rather than the stack address, hence the kmemleak
report. I'll work on a fix/annotation.

-- 
Catalin

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#1499816 — Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning

FromCAI Qian <caiqian@redhat.com>
Date2016-10-12 18:40 +0200
SubjectRe: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning
Message-ID<sruq5-6PD-17@gated-at.bofh.it>
In reply to#1499453

----- Original Message -----
> From: "Catalin Marinas" <catalin.marinas@arm.com>
> To: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org, "Andrew Morton" <akpm@linux-foundation.org>, "Andy Lutomirski" <luto@kernel.org>,
> "CAI Qian" <caiqian@redhat.com>
> Sent: Wednesday, October 12, 2016 5:57:03 AM
> Subject: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning
> 
> Commit 68f24b08ee89 ("sched/core: Free the stack early if
> CONFIG_THREAD_INFO_IN_TASK") may cause the task->stack to be freed
> during kmemleak_scan() execution, leading to either a NULL pointer
> fault (if task->stack is NULL) or kmemleak accessing already freed
> memory. This patch uses the new try_get_task_stack() API to ensure that
> the task stack is not freed during kmemleak stack scanning.
> 
> Fixes: 68f24b08ee89 ("sched/core: Free the stack early if
> CONFIG_THREAD_INFO_IN_TASK")
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: CAI Qian <caiqian@redhat.com>
> Reported-by: CAI Qian <caiqian@redhat.com>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Tested-by: CAI Qian <caiqian@redhat.com>

> ---
> 
> This was reported in a subsequent comment here:
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=173901
> 
> However, the original bugzilla entry doesn't look related to task stack
> freeing as it was first reported on 4.8-rc8. Andy, sorry for cc'ing you
> to bugzilla, please feel free to remove your email from the bug above (I
> can't seem to be able to do it).
> 
>  mm/kmemleak.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index a5e453cf05c4..e5355a5b423f 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -1453,8 +1453,11 @@ static void kmemleak_scan(void)
>  
>  		read_lock(&tasklist_lock);
>  		do_each_thread(g, p) {
> -			scan_block(task_stack_page(p), task_stack_page(p) +
> -				   THREAD_SIZE, NULL);
> +			void *stack = try_get_task_stack(p);
> +			if (stack) {
> +				scan_block(stack, stack + THREAD_SIZE, NULL);
> +				put_task_stack(p);
> +			}
>  		} while_each_thread(g, p);
>  		read_unlock(&tasklist_lock);
>  	}
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
> 
> 
>

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