FAILED: patch "[PATCH] sched/cache: Skip kernel threads for cache aware scheduling" failed to apply to 7.2-stable tree

FAILED: patch "[PATCH] sched/cache: Skip kernel threads for cache aware scheduling" failed to apply to 7.2-stable tree

[gregkh]

The patch below does not apply to the 7.2-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-7.2.y
git checkout FETCH_HEAD
git cherry-pick -x 65efcccddc83d6a19e8a2e2a6117811e39e589bf
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026092935-angelic-kick-1d0a@gregkh' --subject-prefix 'PATCH 7.2.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 65efcccddc83d6a19e8a2e2a6117811e39e589bf Mon Sep 17 00:00:00 2001
From: Chen Yu <yu.c.chen@intel.com>
Date: Mon, 21 Sep 2026 17:37:26 -0700
Subject: [PATCH] sched/cache: Skip kernel threads for cache aware scheduling
 to rubustify the code

Kernel thread should not be covered by cache aware scheduling as
it borrows the statistics from the user space thread. Filter the
kernel thread in account_mm_sched().

In theory a kernel thread does not have any valid
cache group, so !grp should gate the kernel thread.
Add the PF_KTHREAD check explicitly here for safety
reasons, to guard against future modifications and
to pair with task_tick_cache().

Fixes: df0d98475954 ("sched/cache: Introduce infrastructure for cache-aware load balancing")
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: <stable@kernel.org> # 7.2.x
Link: https://patch.msgid.link/058f0c6ea7b991c177a17de347fa3157f25489a7.1790035273.git.tim.c.chen@linux.intel.com

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 974a7dfe3215..57360f5cdde4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1907,8 +1907,14 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	/*
 	 * init_task, kthreads and user thread created
 	 * by user_mode_thread() don't have a cache group.
+	 * In theory a kernel thread does not have any valid
+	 * cache group, because sched_cache_fork() is not
+	 * invoked for a kernel thread - !grp should gate the
+	 * kernel thread. Use the PF_KTHREAD check explicitly
+	 * here for safety reasons, to guard against future
+	 * modifications and to pair with task_tick_cache().
 	 */
-	if (!grp || !grp->pcpu_sched)
+	if (p->flags & PF_KTHREAD || !grp || !grp->pcpu_sched)
 		return;
 
 	pcpu_sched = per_cpu_ptr(grp->pcpu_sched, cpu_of(rq));

Re: FAILED: patch "[PATCH] sched/cache: Skip kernel threads for cache aware scheduling" failed to apply to 7.2-stable tree

[Tim Chen]

On Tue, 2026-09-29 at 13:43 +0200, gregkh@linuxfoundation.org wrote:
> The patch below does not apply to the 7.2-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> To reproduce the conflict and resubmit, you may use the following commands:
> 
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-7.2.y
> git checkout FETCH_HEAD
> git cherry-pick -x 65efcccddc83d6a19e8a2e2a6117811e39e589bf
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026092935-angelic-kick-1d0a@gregkh' --subject-prefix 'PATCH 7.2.y' 'HEAD^..'
> 
> Possible dependencies:
> 

These patches in upstream needs to be applied first before this patch:
f0d243a96f268 sched/fair: Avoid creating misfits during cache-aware balancing (should be included in stable)
28f9c0e0a0b94 sched/cache: Decouple sched_cache_group from mm to fix UAF  (just merged in stable)
b636fef85bda7 sched/cache: Introduce task_struct->sched_cache_grp to fix UAF (should be included in stable)

Thanks.

Tim

> 
> 
> thanks,
> 
> greg k-h
> 
> ------------------ original commit in Linus's tree ------------------
> 
> From 65efcccddc83d6a19e8a2e2a6117811e39e589bf Mon Sep 17 00:00:00 2001
> From: Chen Yu <yu.c.chen@intel.com>
> Date: Mon, 21 Sep 2026 17:37:26 -0700
> Subject: [PATCH] sched/cache: Skip kernel threads for cache aware scheduling
>  to rubustify the code
> 
> Kernel thread should not be covered by cache aware scheduling as
> it borrows the statistics from the user space thread. Filter the
> kernel thread in account_mm_sched().
> 
> In theory a kernel thread does not have any valid
> cache group, so !grp should gate the kernel thread.
> Add the PF_KTHREAD check explicitly here for safety
> reasons, to guard against future modifications and
> to pair with task_tick_cache().
> 
> Fixes: df0d98475954 ("sched/cache: Introduce infrastructure for cache-aware load balancing")
> Signed-off-by: Chen Yu <yu.c.chen@intel.com>
> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Cc: <stable@kernel.org> # 7.2.x
> Link: https://patch.msgid.link/058f0c6ea7b991c177a17de347fa3157f25489a7.1790035273.git.tim.c.chen@linux.intel.com
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 974a7dfe3215..57360f5cdde4 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1907,8 +1907,14 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
>  	/*
>  	 * init_task, kthreads and user thread created
>  	 * by user_mode_thread() don't have a cache group.
> +	 * In theory a kernel thread does not have any valid
> +	 * cache group, because sched_cache_fork() is not
> +	 * invoked for a kernel thread - !grp should gate the
> +	 * kernel thread. Use the PF_KTHREAD check explicitly
> +	 * here for safety reasons, to guard against future
> +	 * modifications and to pair with task_tick_cache().
>  	 */
> -	if (!grp || !grp->pcpu_sched)
> +	if (p->flags & PF_KTHREAD || !grp || !grp->pcpu_sched)
>  		return;
>  
>  	pcpu_sched = per_cpu_ptr(grp->pcpu_sched, cpu_of(rq));

Re: FAILED: patch "[PATCH] sched/cache: Skip kernel threads for cache aware scheduling" failed to apply to 7.2-stable tree

[Greg KH]

On Tue, Sep 29, 2026 at 03:45:46PM -0700, Tim Chen wrote:
> On Tue, 2026-09-29 at 13:43 +0200, gregkh@linuxfoundation.org wrote:
> > The patch below does not apply to the 7.2-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@vger.kernel.org>.
> > 
> > To reproduce the conflict and resubmit, you may use the following commands:
> > 
> > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-7.2.y
> > git checkout FETCH_HEAD
> > git cherry-pick -x 65efcccddc83d6a19e8a2e2a6117811e39e589bf
> > # <resolve conflicts, build, test, etc.>
> > git commit -s
> > git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026092935-angelic-kick-1d0a@gregkh' --subject-prefix 'PATCH 7.2.y' 'HEAD^..'
> > 
> > Possible dependencies:
> > 
> 
> These patches in upstream needs to be applied first before this patch:
> f0d243a96f268 sched/fair: Avoid creating misfits during cache-aware balancing (should be included in stable)
> 28f9c0e0a0b94 sched/cache: Decouple sched_cache_group from mm to fix UAF  (just merged in stable)
> b636fef85bda7 sched/cache: Introduce task_struct->sched_cache_grp to fix UAF (should be included in stable)

Can you send a proper series?

thanks,

greg k-h

Re: FAILED: patch "[PATCH] sched/cache: Skip kernel threads for cache aware scheduling" failed to apply to 7.2-stable tree

[Tim Chen]

On Wed, 2026-09-30 at 14:10 +0200, Greg KH wrote:
> On Tue, Sep 29, 2026 at 03:45:46PM -0700, Tim Chen wrote:
> > On Tue, 2026-09-29 at 13:43 +0200, gregkh@linuxfoundation.org wrote:
> > > The patch below does not apply to the 7.2-stable tree.
> > > If someone wants it applied there, or to any other stable or longterm
> > > tree, then please email the backport, including the original git commit
> > > id to <stable@vger.kernel.org>.
> > > 
> > > To reproduce the conflict and resubmit, you may use the following commands:
> > > 
> > > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-7.2.y
> > > git checkout FETCH_HEAD
> > > git cherry-pick -x 65efcccddc83d6a19e8a2e2a6117811e39e589bf
> > > # <resolve conflicts, build, test, etc.>
> > > git commit -s
> > > git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026092935-angelic-kick-1d0a@gregkh' --subject-prefix 'PATCH 7.2.y' 'HEAD^..'
> > > 
> > > Possible dependencies:
> > > 
> > 
> > These patches in upstream needs to be applied first before this patch:
> > f0d243a96f268 sched/fair: Avoid creating misfits during cache-aware balancing (should be included in stable)
> > 28f9c0e0a0b94 sched/cache: Decouple sched_cache_group from mm to fix UAF  (just merged in stable)
> > b636fef85bda7 sched/cache: Introduce task_struct->sched_cache_grp to fix UAF (should be included in stable)
> 
> Can you send a proper series?

Hi Greg,

Sorry for the troubles.  I have sent you a series that included
all the patches.  Some you may have already applied but I still
included them so show the order of the patches.

Thanks.

Tim

> 
> thanks,
> 
> greg k-h