The patch below does not apply to the 4.19-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@xxxxxxxxxxxxxxx>.
Possible dependencies:
fe1f0714385f ("x86/resctrl: Fix task CLOSID/RMID update race")
e0ad6dc8969f ("x86/resctrl: Use task_curr() instead of task_struct->on_cpu to prevent unnecessary IPI")
ae28d1aae48a ("x86/resctrl: Use an IPI instead of task_work_add() to update PQR_ASSOC MSR")
758999246965 ("x86/resctrl: Add necessary kernfs_put() calls to prevent refcount leak")
fd8d9db3559a ("x86/resctrl: Remove superfluous kernfs_get() calls to prevent refcount leak")
91989c707884 ("task_work: cleanup notification modes")
216578e55ac9 ("io_uring: fix REQ_F_COMP_LOCKED by killing it")
4edf20f99902 ("io_uring: dig out COMP_LOCK from deep call chain")
b1b74cfc1967 ("io_uring: don't unnecessarily clear F_LINK_TIMEOUT")
6ad4bf6ea160 ("Merge tag 'io_uring-5.10-2020-10-12' of git://git.kernel.dk/linux-block")
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From fe1f0714385fbcf76b0cbceb02b7277d842014fc Mon Sep 17 00:00:00 2001
From: Peter Newman <peternewman@xxxxxxxxxx>
Date: Tue, 20 Dec 2022 17:11:23 +0100
Subject: [PATCH] x86/resctrl: Fix task CLOSID/RMID update race
When the user moves a running task to a new rdtgroup using the task's
file interface or by deleting its rdtgroup, the resulting change in
CLOSID/RMID must be immediately propagated to the PQR_ASSOC MSR on the
task(s) CPUs.
x86 allows reordering loads with prior stores, so if the task starts
running between a task_curr() check that the CPU hoisted before the
stores in the CLOSID/RMID update then it can start running with the old
CLOSID/RMID until it is switched again because __rdtgroup_move_task()
failed to determine that it needs to be interrupted to obtain the new
CLOSID/RMID.
Refer to the diagram below:
CPU 0 CPU 1
----- -----
__rdtgroup_move_task():
curr <- t1->cpu->rq->curr
__schedule():
rq->curr <- t1
resctrl_sched_in():
t1->{closid,rmid} -> {1,1}
t1->{closid,rmid} <- {2,2}
if (curr == t1) // false
IPI(t1->cpu)
A similar race impacts rdt_move_group_tasks(), which updates tasks in a
deleted rdtgroup.
In both cases, use smp_mb() to order the task_struct::{closid,rmid}
stores before the loads in task_curr(). In particular, in the
rdt_move_group_tasks() case, simply execute an smp_mb() on every
iteration with a matching task.
It is possible to use a single smp_mb() in rdt_move_group_tasks(), but
this would require two passes and a means of remembering which
task_structs were updated in the first loop. However, benchmarking
results below showed too little performance impact in the simple
approach to justify implementing the two-pass approach.
Times below were collected using `perf stat` to measure the time to
remove a group containing a 1600-task, parallel workload.
CPU: Intel(R) Xeon(R) Platinum P-8136 CPU @ 2.00GHz (112 threads)
# mkdir /sys/fs/resctrl/test
# echo $$ > /sys/fs/resctrl/test/tasks
# perf bench sched messaging -g 40 -l 100000
task-clock time ranges collected using:
# perf stat rmdir /sys/fs/resctrl/test
Baseline: 1.54 - 1.60 ms
smp_mb() every matching task: 1.57 - 1.67 ms
[ bp: Massage commit message. ]
Fixes: ae28d1aae48a ("x86/resctrl: Use an IPI instead of task_work_add() to update PQR_ASSOC MSR")
Fixes: 0efc89be9471 ("x86/intel_rdt: Update task closid immediately on CPU in rmdir and unmount")
Signed-off-by: Peter Newman <peternewman@xxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Reviewed-by: Babu Moger <babu.moger@xxxxxxx>
Cc: <stable@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20221220161123.432120-1-peternewman@xxxxxxxxxx
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index e5a48f05e787..5993da21d822 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -580,8 +580,10 @@ static int __rdtgroup_move_task(struct task_struct *tsk,
/*
* Ensure the task's closid and rmid are written before determining if
* the task is current that will decide if it will be interrupted.
+ * This pairs with the full barrier between the rq->curr update and
+ * resctrl_sched_in() during context switch.
*/
- barrier();
+ smp_mb();
/*
* By now, the task's closid and rmid are set. If the task is current
@@ -2401,6 +2403,14 @@ static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to,
WRITE_ONCE(t->closid, to->closid);
WRITE_ONCE(t->rmid, to->mon.rmid);
+ /*
+ * Order the closid/rmid stores above before the loads
+ * in task_curr(). This pairs with the full barrier
+ * between the rq->curr update and resctrl_sched_in()
+ * during context switch.
+ */
+ smp_mb();
+
/*
* If the task is on a CPU, set the CPU in the mask.
* The detection is inaccurate as tasks might move or
