Oops occur when running qemu on arm64:
Unable to handle kernel paging request at virtual address ffff000008effe40
Internal error: Oops: 96000007 [#1] SMP
Process migration/0 (pid: 12, stack limit = 0x00000000084e3736)
pstate: 20000085 (nzCv daIf -PAN -UAO)
pc : __ll_sc___cmpxchg_case_acq_4+0x4/0x20
lr : move_queued_task.isra.21+0x124/0x298
...
Call trace:
__ll_sc___cmpxchg_case_acq_4+0x4/0x20
__migrate_task+0xc8/0xe0
migration_cpu_stop+0x170/0x180
cpu_stopper_thread+0xec/0x178
smpboot_thread_fn+0x1ac/0x1e8
kthread+0x134/0x138
ret_from_fork+0x10/0x18
__set_cpus_allowed_ptr will choose an active dest_cpu in affinity mask to
migrage the process if process is not currently running on any one of the
CPUs specified in affinity mask. __set_cpus_allowed_ptr will choose an
invalid dest_cpu (dest_cpu >= nr_cpu_ids, 1024 in my virtual machine) if
CPUS in an affinity mask are deactived by cpu_down after cpumask_intersects
check. cpumask_test_cpu of dest_cpu afterwards is overflow and may pass if
corresponding bit is coincidentally set. As a consequence, kernel will
access an invalid rq address associate with the invalid cpu in
migration_cpu_stop->__migrate_task->move_queued_task and the Oops occurs.
Process as follows may trigger the Oops:
1) A process repeatedly binds itself to cpu0 and cpu1 in turn by calling
sched_setaffinity.
2) A shell script repeatedly "echo 0 > /sys/devices/system/cpu/cpu1/online"
and "echo 1 > /sys/devices/system/cpu/cpu1/online" in turn.
3) Oops appears if the invalid cpu is set in memory after tested cpumask.
Signed-off-by: KeMeng Shi <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
---
Changes in v2:
-solve format problems in log
kernel/sched/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3c7b90bcbe4e..087f4ac30b60 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1656,7 +1656,8 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
if (cpumask_equal(p->cpus_ptr, new_mask))
goto out;
- if (!cpumask_intersects(new_mask, cpu_valid_mask)) {
+ dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask);
+ if (dest_cpu >= nr_cpu_ids) {
ret = -EINVAL;
goto out;
}
@@ -1677,7 +1678,6 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
if (cpumask_test_cpu(task_cpu(p), new_mask))
goto out;
- dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask);
if (task_running(rq, p) || p->state == TASK_WAKING) {
struct migration_arg arg = { p, dest_cpu };
/* Need help from migration thread: drop lock and wait. */
--
2.19.1
On Mon, Sep 16, 2019 at 06:53:28AM +0000, KeMeng Shi wrote:
> Oops occur when running qemu on arm64:
> Unable to handle kernel paging request at virtual address ffff000008effe40
> Internal error: Oops: 96000007 [#1] SMP
> Process migration/0 (pid: 12, stack limit = 0x00000000084e3736)
> pstate: 20000085 (nzCv daIf -PAN -UAO)
> pc : __ll_sc___cmpxchg_case_acq_4+0x4/0x20
> lr : move_queued_task.isra.21+0x124/0x298
> ...
> Call trace:
> __ll_sc___cmpxchg_case_acq_4+0x4/0x20
> __migrate_task+0xc8/0xe0
> migration_cpu_stop+0x170/0x180
> cpu_stopper_thread+0xec/0x178
> smpboot_thread_fn+0x1ac/0x1e8
> kthread+0x134/0x138
> ret_from_fork+0x10/0x18
>
> __set_cpus_allowed_ptr will choose an active dest_cpu in affinity mask to
> migrage the process if process is not currently running on any one of the
> CPUs specified in affinity mask. __set_cpus_allowed_ptr will choose an
> invalid dest_cpu (dest_cpu >= nr_cpu_ids, 1024 in my virtual machine) if
> CPUS in an affinity mask are deactived by cpu_down after cpumask_intersects
> check. cpumask_test_cpu of dest_cpu afterwards is overflow and may pass if
> corresponding bit is coincidentally set. As a consequence, kernel will
> access an invalid rq address associate with the invalid cpu in
> migration_cpu_stop->__migrate_task->move_queued_task and the Oops occurs.
>
> Process as follows may trigger the Oops:
> 1) A process repeatedly binds itself to cpu0 and cpu1 in turn by calling
> sched_setaffinity.
> 2) A shell script repeatedly "echo 0 > /sys/devices/system/cpu/cpu1/online"
> and "echo 1 > /sys/devices/system/cpu/cpu1/online" in turn.
> 3) Oops appears if the invalid cpu is set in memory after tested cpumask.
>
> Signed-off-by: KeMeng Shi <[email protected]>
> Reviewed-by: Valentin Schneider <[email protected]>
> ---
> Changes in v2:
> -solve format problems in log
>
> kernel/sched/core.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3c7b90bcbe4e..087f4ac30b60 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1656,7 +1656,8 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
> if (cpumask_equal(p->cpus_ptr, new_mask))
> goto out;
>
> - if (!cpumask_intersects(new_mask, cpu_valid_mask)) {
> + dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask);
> + if (dest_cpu >= nr_cpu_ids) {
> ret = -EINVAL;
> goto out;
> }
> @@ -1677,7 +1678,6 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
> if (cpumask_test_cpu(task_cpu(p), new_mask))
> goto out;
>
> - dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask);
> if (task_running(rq, p) || p->state == TASK_WAKING) {
> struct migration_arg arg = { p, dest_cpu };
> /* Need help from migration thread: drop lock and wait. */
> --
> 2.19.1
>
>
The cpu_active_mask might have changed in between. Your fix looks good to me.
Thanks,
Pavan
--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 714e501e16cd473538b609b3e351b2cc9f7f09ed
Gitweb: https://git.kernel.org/tip/714e501e16cd473538b609b3e351b2cc9f7f09ed
Author: KeMeng Shi <[email protected]>
AuthorDate: Mon, 16 Sep 2019 06:53:28
Committer: Ingo Molnar <[email protected]>
CommitterDate: Wed, 25 Sep 2019 17:42:31 +02:00
sched/core: Fix migration to invalid CPU in __set_cpus_allowed_ptr()
An oops can be triggered in the scheduler when running qemu on arm64:
Unable to handle kernel paging request at virtual address ffff000008effe40
Internal error: Oops: 96000007 [#1] SMP
Process migration/0 (pid: 12, stack limit = 0x00000000084e3736)
pstate: 20000085 (nzCv daIf -PAN -UAO)
pc : __ll_sc___cmpxchg_case_acq_4+0x4/0x20
lr : move_queued_task.isra.21+0x124/0x298
...
Call trace:
__ll_sc___cmpxchg_case_acq_4+0x4/0x20
__migrate_task+0xc8/0xe0
migration_cpu_stop+0x170/0x180
cpu_stopper_thread+0xec/0x178
smpboot_thread_fn+0x1ac/0x1e8
kthread+0x134/0x138
ret_from_fork+0x10/0x18
__set_cpus_allowed_ptr() will choose an active dest_cpu in affinity mask to
migrage the process if process is not currently running on any one of the
CPUs specified in affinity mask. __set_cpus_allowed_ptr() will choose an
invalid dest_cpu (dest_cpu >= nr_cpu_ids, 1024 in my virtual machine) if
CPUS in an affinity mask are deactived by cpu_down after cpumask_intersects
check. cpumask_test_cpu() of dest_cpu afterwards is overflown and may pass if
corresponding bit is coincidentally set. As a consequence, kernel will
access an invalid rq address associate with the invalid CPU in
migration_cpu_stop->__migrate_task->move_queued_task and the Oops occurs.
The reproduce the crash:
1) A process repeatedly binds itself to cpu0 and cpu1 in turn by calling
sched_setaffinity.
2) A shell script repeatedly does "echo 0 > /sys/devices/system/cpu/cpu1/online"
and "echo 1 > /sys/devices/system/cpu/cpu1/online" in turn.
3) Oops appears if the invalid CPU is set in memory after tested cpumask.
Signed-off-by: KeMeng Shi <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
kernel/sched/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2d9a394..83ea23e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1656,7 +1656,8 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
if (cpumask_equal(p->cpus_ptr, new_mask))
goto out;
- if (!cpumask_intersects(new_mask, cpu_valid_mask)) {
+ dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask);
+ if (dest_cpu >= nr_cpu_ids) {
ret = -EINVAL;
goto out;
}
@@ -1677,7 +1678,6 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
if (cpumask_test_cpu(task_cpu(p), new_mask))
goto out;
- dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask);
if (task_running(rq, p) || p->state == TASK_WAKING) {
struct migration_arg arg = { p, dest_cpu };
/* Need help from migration thread: drop lock and wait. */