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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?d98lNisQgtF6a2v23gIOA+OQpmRtrhl9P03jIJ1ta3cm3WfdV1KKlkiNtHJP?= =?us-ascii?Q?KemnvCycNNSI1ejR0xbLQpw5vexzQrKI7XM/4oYUN2Xh1IbBBbJITrnWCzbO?= =?us-ascii?Q?JEj+Di8G+qKDx8ZY5CvYRGNRZ2zy5QhpNC67VKOPKT2KfbmAmtAW3tJF7knb?= =?us-ascii?Q?zhfGaDDFHRvgpNa44YgArN2lFyTBtQVZR/9CCqbvcCH7guzPkOpoW5pAJVoW?= =?us-ascii?Q?18hrOFsbfzjLN6l8jcWThnEg1bpWY/pM11kjwQsUpVXBQr9uJiuRM+5kBByB?= =?us-ascii?Q?6B5xIyxV+WgUFGTh9QbLJ3HNxDX3o3qg7uF/yEerEFgtKHHIOn9oVopEdp+5?= =?us-ascii?Q?1LY9eramyGgFZrvbPv69FNXfckd7sJkmC8XxZcbRqU5FUqvyqSOvF6g6bN8x?= =?us-ascii?Q?PVxXBpK0sLj3ULmxcy8RUWfKB4Yay6YpjBNCD85Nz7Ac8nuV1y8mtYn7+uPi?= =?us-ascii?Q?kxwuxYnV3oTNHNq3lOxUtXOT/AEPeHsOfZHku3YbArIZ+PET5KdMRrBGa2HA?= =?us-ascii?Q?EBJi2xRnCkembFOYZto7nMDoJIcUy02PjhNstdUYSG/fY/j/YAsfQnJmp6L3?= =?us-ascii?Q?3IiyZbSlw10dBAkbDur4/zz86KAiOt63PC804gSRN1//7nm39CI+umtkqq3Z?= =?us-ascii?Q?t54e2ddwK7xqgvc8uZs7IWYnSuRunxyxyCOrZQ1px4tOQVgc6yZ+0BjuTQIr?= =?us-ascii?Q?uPtk/zJUfI6ixGtn1ZGALpuc2AF2gNCPgjbNmvDst80AuyNAyot/APf7cRxp?= =?us-ascii?Q?4Gfz+eDXTYiHqpORY/VKGcXuznZ5k0715N6rdrteurUdFKMsBW6lZ0AHjRRH?= =?us-ascii?Q?M0f+7+3ksZrSlI06Je4cZXLnUQVx/bJRMawdJMK6GSVCY5aK2cIqByvURCnL?= =?us-ascii?Q?aHKDKDa+byvVC0kF+/72Np/5o73KXn++L2m+X+H1c5o4Y9xoZFIlaPVyVCpY?= =?us-ascii?Q?NUW0IZvqsq05L67HCRWXGLjEWqyH0zyNT6B0yUjBB5ngZR+N3pkPv8Oxe9Nk?= =?us-ascii?Q?uuFLYrYtwZ5znWnG/+/FJDFc8gQnwSjYfdppxOMRjQLoYBoRL6WSU53hfiAv?= =?us-ascii?Q?y77UYRI5vMSn9U+PCEXYk6iidwdRFte09ybRN7ps9IoLfxGUL4Pz7gJfCG5D?= =?us-ascii?Q?ZGWmPv6eNPOImehvf2PfHiwSMzM2/XToFkeW24u16SOCzFb3MQYCv5P4G0ko?= =?us-ascii?Q?V3bvM1fOYPQmZRO+Liry2Q8JQmaqOO/mTDSylQdYskX6cFZ8FlLJjjWh3BGH?= =?us-ascii?Q?NblSSTUitH/PLdZJ1mfzKrdfV17rqxoUTcsQ6m4QOoP0ng6asGkkhiwpPOEV?= =?us-ascii?Q?YyW73VWkJfZGOHgT/GLaXgGEG8b0sceWw+N00rFdWY6q6izVT08MXOjWPaBy?= =?us-ascii?Q?vgBqqrPZts1bBtm8CuTnNMYF4LtYngYjkKTMU2QIbbAagdXM1BZg88V1MVHg?= =?us-ascii?Q?OvqzWWM8u6xvU5MIzT8+m7cOe3gzRstNNbsE8Nu9mVO4+TQ+5xTakye2XbC3?= =?us-ascii?Q?LdOnbPK5SQQSsk64uYGk2JnaO3HLesm3eHjfvLtEellQW3BIxgGR5FILK2Yo?= =?us-ascii?Q?ZSbnqzQa/NGcdC3rcC2b6UAxevCbuoGsBQ+MoOZc?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 9539c435-7b19-4533-58d4-08ddd3559db4 X-MS-Exchange-CrossTenant-AuthSource: LV8PR12MB9620.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Aug 2025 12:51:23.0329 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: ezh6GSiQ3gqJD2+l+tleUAVNJS8pV/4mn0gRyB/TRjyDXv77wTLyLTTOIUrQtievpf5yCMLd4vhN5UFPdBd7vA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB4207 On Mon, Aug 04, 2025 at 12:27:42PM +0100, Christian Loehle wrote: > Provide scx_bpf_remote_curr() as a way for scx schedulers to > check the curr task of a remote rq, without assuming its lock > is held. > > Many scx schedulers make use of scx_bpf_cpu_rq() to check a > remote curr (e.g. to see if it should be preempted). This is > problematic because scx_bpf_cpu_rq() provides access to all > fields of struct rq, most of which aren't safe to use without > holding the associated rq lock. > > Signed-off-by: Christian Loehle > --- > kernel/sched/ext.c | 24 ++++++++++++++++++++++++ > tools/sched_ext/include/scx/common.bpf.h | 1 + > 2 files changed, 25 insertions(+) > > diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c > index 3ea3f0f18030..1d9d9cbed0aa 100644 > --- a/kernel/sched/ext.c > +++ b/kernel/sched/ext.c > @@ -7426,6 +7426,29 @@ __bpf_kfunc struct rq *scx_bpf_cpu_rq(s32 cpu) > return cpu_rq(cpu); > } > > +struct task_struct *bpf_task_acquire(struct task_struct *p); Can we move include all the way to the top? In this way we don't have to add this forward declaration. > + > +/** > + * scx_bpf_remote_curr - Fetch the curr of a rq without acquiring its rq lock > + * @cpu: CPU of the rq > + * > + * Increments the refcount of the task_struct which needs to be released later. Maybe we should mention that the task must be released by calling bpf_task_release(). While at it, what do you think about renaming this to something like scx_bpf_task_acquire_on_cpu(), so that it looks similar to bpf_task_acquire()? > + */ > +__bpf_kfunc struct task_struct *scx_bpf_remote_curr(s32 cpu) > +{ > + struct task_struct *p; > + > + if (!kf_cpu_valid(cpu, NULL)) > + return NULL; > + > + rcu_read_lock(); > + p = cpu_rq(cpu)->curr; > + if (p) > + p = bpf_task_acquire(p); > + rcu_read_unlock(); > + return p; > +} > + > /** > * scx_bpf_task_cgroup - Return the sched cgroup of a task > * @p: task of interest > @@ -7590,6 +7613,7 @@ BTF_ID_FLAGS(func, scx_bpf_put_cpumask, KF_RELEASE) > BTF_ID_FLAGS(func, scx_bpf_task_running, KF_RCU) > BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU) > BTF_ID_FLAGS(func, scx_bpf_cpu_rq, KF_RET_NULL) > +BTF_ID_FLAGS(func, scx_bpf_remote_curr, KF_RET_NULL | KF_ACQUIRE) > #ifdef CONFIG_CGROUP_SCHED > BTF_ID_FLAGS(func, scx_bpf_task_cgroup, KF_RCU | KF_ACQUIRE) > #endif > diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h > index d4e21558e982..e5d4ef124532 100644 > --- a/tools/sched_ext/include/scx/common.bpf.h > +++ b/tools/sched_ext/include/scx/common.bpf.h > @@ -91,6 +91,7 @@ s32 scx_bpf_pick_any_cpu(const cpumask_t *cpus_allowed, u64 flags) __ksym; > bool scx_bpf_task_running(const struct task_struct *p) __ksym; > s32 scx_bpf_task_cpu(const struct task_struct *p) __ksym; > struct rq *scx_bpf_cpu_rq(s32 cpu) __ksym; > +struct task_struct *scx_bpf_remote_curr(s32 cpu) __ksym; > struct cgroup *scx_bpf_task_cgroup(struct task_struct *p) __ksym __weak; > u64 scx_bpf_now(void) __ksym __weak; > void scx_bpf_events(struct scx_event_stats *events, size_t events__sz) __ksym __weak; > -- > 2.34.1 > Thanks, -Andrea