A crash was observed when the sched_ext selftests runner was
terminated with Ctrl+\ while test 15 was running:
NIP [c00000000028fa58] scx_enable.constprop.0+0x358/0x12b0
LR [c00000000028fa2c] scx_enable.constprop.0+0x32c/0x12b0
Call Trace:
scx_enable.constprop.0+0x32c/0x12b0 (unreliable)
bpf_struct_ops_link_create+0x18c/0x22c
__sys_bpf+0x23f8/0x3044
sys_bpf+0x2c/0x6c
system_call_exception+0x124/0x320
system_call_vectored_common+0x15c/0x2ec
kthread_run_worker() returns an ERR_PTR() on failure rather than NULL,
but the current code in scx_alloc_and_add_sched() only checks for a NULL
helper. Incase of failure on SIGQUIT, the error is not handled in
scx_alloc_and_add_sched() and scx_enable() ends up dereferencing an
error pointer.
Error handling is fixed in scx_alloc_and_add_sched() to propagate
PTR_ERR() into ret, so that scx_enable() jumps to the existing error
path, avoiding random dereference on failure.
Fixes: bff3b5aec1 ("sched_ext: Move disable machinery into scx_sched")
Cc: stable@vger.kernel.org # v6.16+
Reported-and-tested-by: Samir Mulani <samir@linux.ibm.com>
Signed-off-by: Saket Kumar Bhaskar <skb99@linux.ibm.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Reviewed-by: Vishal Chourasia <vishalc@linux.ibm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
For PREEMPT_RT kernels, the kick_cpus_irq_workfn() be invoked in
the per-cpu irq_work/* task context and there is no rcu-read critical
section to protect. this commit therefore use IRQ_WORK_INIT_HARD() to
initialize the per-cpu rq->scx.kick_cpus_irq_work in the
init_sched_ext_class().
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Signed-off-by: Tejun Heo <tj@kernel.org>
For PREEMPT_RT=y kernels, the deferred_irq_workfn() is executed in
the per-cpu irq_work/* task context and not disable-irq, if the rq
returned by container_of() is current CPU's rq, the following scenarios
may occur:
lock(&rq->__lock);
<Interrupt>
lock(&rq->__lock);
This commit use IRQ_WORK_INIT_HARD() to replace init_irq_work() to
initialize rq->scx.deferred_irq_work, make the deferred_irq_workfn()
is always invoked in hard-irq context.
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Signed-off-by: Tejun Heo <tj@kernel.org>
Update scx_task_locks so that it's safe to lock/unlock in a
non-sleepable context in PREEMPT_RT kernels. scx_task_locks is
(non-raw) spinlock used to protect the list of tasks under SCX.
This list is updated during from finish_task_switch(), which
cannot sleep. Regular spinlocks can be locked in such a context
in non-RT kernels, but are sleepable under when CONFIG_PREEMPT_RT=y.
Convert scx_task_locks into a raw spinlock, which is not sleepable
even on RT kernels.
Sample backtrace:
<TASK>
dump_stack_lvl+0x83/0xa0
__might_resched+0x14a/0x200
rt_spin_lock+0x61/0x1c0
? sched_ext_dead+0x2d/0xf0
? lock_release+0xc6/0x280
sched_ext_dead+0x2d/0xf0
? srso_alias_return_thunk+0x5/0xfbef5
finish_task_switch.isra.0+0x254/0x360
__schedule+0x584/0x11d0
? srso_alias_return_thunk+0x5/0xfbef5
? srso_alias_return_thunk+0x5/0xfbef5
? tick_nohz_idle_exit+0x7e/0x120
schedule_idle+0x23/0x40
cpu_startup_entry+0x29/0x30
start_secondary+0xf8/0x100
common_startup_64+0x13e/0x148
</TASK>
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_bpf_cpuperf_set() has a typo where it dereferences the local
variable @sch, instead of the global @scx_root pointer. Fix by
dereferencing the correct variable.
Fixes: 956f2b11a8 ("sched_ext: Drop kf_cpu_valid()")
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
When scheduling the deferred balance callbacks, check SCX_RQ_BAL_CB_PENDING
instead of SCX_RQ_BAL_PENDING. This way schedule_deferred() properly tests
whether there is already a pending request for queue_balance_callback() to
be invoked at the end of .balance().
Fixes: a8ad873113 ("sched_ext: defer queue_balance_callback() until after ops.dispatch")
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
If we load a BPF scheduler while another scheduler is already running,
alloc_kick_pseqs() would be called again, overwriting the previously
allocated arrays.
Fix by moving the alloc_kick_pseqs() call after the scx_enable_state()
check, ensuring that the arrays are only allocated when a scheduler can
actually be loaded.
Fixes: 14c1da3895 ("sched_ext: Allocate scx_kick_cpus_pnt_seqs lazily using kvzalloc()")
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
On systems with >4096 CPUs, scx_kick_cpus_pnt_seqs allocation fails during
boot because it exceeds the 32,768 byte percpu allocator limit.
Restructure to use DEFINE_PER_CPU() for the per-CPU pointers, with each CPU
pointing to its own kvzalloc'd array. Move allocation from boot time to
scx_enable() and free in scx_disable(), so the O(nr_cpu_ids^2) memory is only
consumed when sched_ext is active.
Use RCU to guard against racing with free. Arrays are freed via call_rcu()
and kick_cpus_irq_workfn() uses rcu_dereference_bh() with a NULL check.
While at it, rename to scx_kick_pseqs for brevity and update comments to
clarify these are pick_task sequence numbers.
v2: RCU protect scx_kick_seqs to manage kick_cpus_irq_workfn() racing
against disable as per Andrea.
v3: Fix bugs notcied by Andrea.
Reported-by: Phil Auld <pauld@redhat.com>
Link: http://lkml.kernel.org/r/20251007133523.GA93086@pauld.westford.csb
Cc: Andrea Righi <arighi@nvidia.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Phil Auld <pauld@redhat.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
The sched_ext code calls queue_balance_callback() during enqueue_task()
to defer operations that drop multiple locks until we can unpin them.
The call assumes that the rq lock is held until the callbacks are
invoked, and the pending callbacks will not be visible to any other
threads. This is enforced by a WARN_ON_ONCE() in rq_pin_lock().
However, balance_one() may actually drop the lock during a BPF dispatch
call. Another thread may win the race to get the rq lock and see the
pending callback. To avoid this, sched_ext must only queue the callback
after the dispatch calls have completed.
CPU 0 CPU 1 CPU 2
scx_balance()
rq_unpin_lock()
scx_balance_one()
|= IN_BALANCE scx_enqueue()
ops.dispatch()
rq_unlock()
rq_lock()
queue_balance_callback()
rq_unlock()
[WARN] rq_pin_lock()
rq_lock()
&= ~IN_BALANCE
rq_repin_lock()
Changelog
v2-> v1 (https://lore.kernel.org/sched-ext/aOgOxtHCeyRT_7jn@gpd4)
- Fixed explanation in patch description (Andrea)
- Fixed scx_rq mask state updates (Andrea)
- Added Reviewed-by tag from Andrea
Reported-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Emil Tsalapatis (Meta) <emil@etsalapatis.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
By the time scx_sched_free_rcu_work() runs, the scx_sched is no longer
reachable. However, a previously queued error_irq_work may still be pending or
running. Ensure it completes before proceeding with teardown.
Fixes: bff3b5aec1 ("sched_ext: Move disable machinery into scx_sched")
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_bpf_dsq_move_set_slice() and scx_bpf_dsq_move_set_vtime() take a DSQ
iterator argument which has to be valid. Mark them with KF_RCU.
Fixes: 4c30f5ce4f ("sched_ext: Implement scx_bpf_dispatch[_vtime]_from_dsq()")
Cc: stable@vger.kernel.org # v6.12+
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Pull sched_ext/for-6.17-fixes to receive:
55ed11b181 ("sched_ext: idle: Handle migration-disabled tasks in BPF code")
which conflicts with the following commit in for-6.18:
2407bae23d ("sched_ext: Add the @sch parameter to ext_idle helpers")
The conflict is a simple context conflict which can be resolved by taking
the updated parts from both commits.
Signed-off-by: Tejun Heo <tj@kernel.org>
In preparation for multiple scheduler support:
- Add the @sch parameter to find_global_dsq() and refill_task_slice_dfl().
- Restructure scx_allow_ttwu_queue() and make it read scx_root into $sch.
- Make RCU protection in scx_dsq_move() and scx_bpf_dsq_move_to_local()
explicit.
v2: Add scx_root -> sch conversion in scx_allow_ttwu_queue().
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
The intention behind scx_kf_exit/error() was that when called from kfuncs,
scx_kf_exit/error() would be able to implicitly determine the scx_sched
instance being operated on and thus wouldn't need the @sch parameter passed
in explicitly. This turned out to be unnecessarily complicated to implement
and not have enough practical benefits. Replace scx_kf_exit/error() usages
with scx_exit/error() which take an explicit @sch parameter.
- Add the @sch parameter to scx_kf_allowed(), scx_kf_allowed_on_arg_tasks,
mark_direct_dispatch() and other intermediate functions transitively.
- In callers that don't already have @sch available, grab RCU, read
$scx_root, verify it's not NULL and use it.
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
In preparation for multiple scheduler support, add the @sch parameter to
scx_dsq_insert_preamble/commit() and update the callers to read $scx_root
and pass it in. The passed in @sch parameter is not used yet.
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
The intention behind kf_cpu_valid() was that when called from kfuncs,
kf_cpu_valid() would be able to implicitly determine the scx_sched instance
being operated on and thus wouldn't need @sch passed in explicitly. This
turned out to be unnecessarily complicated to implement and not have
justifiable practical benefits. Replace kf_cpu_valid() usages with
ops_cpu_valid() which takes explicit @sch.
Callers which don't have $sch available in the context are updated to read
$scx_root under RCU read lock, verify that it's not NULL and pass it in.
scx_bpf_cpu_rq() is restructured to use guard(rcu)() instead of explicit
rcu_read_[un]lock().
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
In preparation for multiple scheduler support, add the @sch parameter to
__bstr_format() and update the callers to read $scx_root, verify that it's
not NULL and pass it in. The passed in @sch parameter is not used yet.
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
In preparation for multiple scheduler support, separate out scx_kick_cpu()
from scx_bpf_kick_cpu() and add the @sch parameter to it. scx_bpf_kick_cpu()
now acquires an RCU read lock, reads $scx_root, and calls scx_kick_cpu()
with it if non-NULL. The passed in @sch parameter is not used yet.
Internal uses of scx_bpf_kick_cpu() are converted to scx_kick_cpu(). Where
$sch is available, it's used. In the pick_task_scx() path where no
associated scheduler can be identified, $scx_root is used directly. Note
that $scx_root cannot be NULL in this case.
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
ops.exit() may be called even if the loading failed before ops.init()
finishes successfully. This is because ops.exit() allows rich exit info
communication. Add SCX_EFLAG_INITIALIZED flag to scx_exit_info.flags to
indicate whether ops.init() finished successfully.
This enables BPF schedulers to distinguish between exit scenarios and
handle cleanup appropriately based on initialization state.
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
task_can_run_on_remote_rq() takes @sch but it is using scx_root when
incrementing SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE, which is inconsistent and
gets in the way of implementing multiple scheduler support. Use @sch
instead. As currently scx_root is the only possible scheduler instance, this
doesn't cause any behavior changes.
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
The find_user_dsq() function is called from contexts that are already
under RCU read lock protection. Switch from rhashtable_lookup_fast() to
rhashtable_lookup() to avoid redundant RCU locking.
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_bpf_cpu_curr() has been introduced to retrieve the current task of a
given runqueue, allowing schedulers to interact with that task.
The kfunc assumes that it is always called in an RCU context, but this
is not always guaranteed and some BPF schedulers can trigger the
following warning:
WARNING: suspicious RCU usage
sched_ext: BPF scheduler "cosmos_1.0.2_gd0e71ca_x86_64_unknown_linux_gnu_debug" enabled
6.17.0-rc1 #1-NixOS Not tainted
-----------------------------
kernel/sched/ext.c:6415 suspicious rcu_dereference_check() usage!
...
Call Trace:
<IRQ>
dump_stack_lvl+0x6f/0xb0
lockdep_rcu_suspicious.cold+0x4e/0x96
scx_bpf_cpu_curr+0x7e/0x80
bpf_prog_c68b2b6b6b1b0ff8_sched_timerfn+0xce/0x1dc
bpf_timer_cb+0x7b/0x130
__hrtimer_run_queues+0x1ea/0x380
hrtimer_run_softirq+0x8c/0xd0
handle_softirqs+0xc9/0x3b0
__irq_exit_rcu+0x96/0xc0
irq_exit_rcu+0xe/0x20
sysvec_apic_timer_interrupt+0x73/0x80
</IRQ>
<TASK>
To address this, mark the kfunc with KF_RCU_PROTECTED, so the verifier
can enforce its usage only inside RCU-protected sections.
Note: this also requires commit 1512231b6c ("bpf: Enforce RCU protection
for KF_RCU_PROTECTED"), currently in bpf-next, to enforce the proper
KF_RCU_PROTECTED.
Fixes: 20b158094a ("sched_ext: Introduce scx_bpf_cpu_curr()")
Cc: Christian Loehle <christian.loehle@arm.com>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Include the task's migration-disabled counter when dumping task state
during an error exit.
This can help diagnose cases where tasks can get stuck, because they're
unable to migrate elsewhere.
tj: s/nomig/no_mig/ for readability and consistency with other keys.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_bpf_reenqueue_local() can be called from ops.cpu_release() when a
CPU is taken by a higher scheduling class to give tasks queued to the
CPU's local DSQ a chance to be migrated somewhere else, instead of
waiting indefinitely for that CPU to become available again.
In doing so, we decided to skip migration-disabled tasks, under the
assumption that they cannot be migrated anyway.
However, when a higher scheduling class preempts a CPU, the running task
is always inserted at the head of the local DSQ as a migration-disabled
task. This means it is always skipped by scx_bpf_reenqueue_local(), and
ends up being confined to the same CPU even if that CPU is heavily
contended by other higher scheduling class tasks.
As an example, let's consider the following scenario:
$ schedtool -a 0,1, -e yes > /dev/null
$ sudo schedtool -F -p 99 -a 0, -e \
stress-ng -c 1 --cpu-load 99 --cpu-load-slice 1000
The first task (SCHED_EXT) can run on CPU0 or CPU1. The second task
(SCHED_FIFO) is pinned to CPU0 and consumes ~99% of it. If the SCHED_EXT
task initially runs on CPU0, it will remain there because it always sees
CPU0 as "idle" in the short gaps left by the RT task, resulting in ~1%
utilization while CPU1 stays idle:
0[||||||||||||||||||||||100.0%] 8[ 0.0%]
1[ 0.0%] 9[ 0.0%]
2[ 0.0%] 10[ 0.0%]
3[ 0.0%] 11[ 0.0%]
4[ 0.0%] 12[ 0.0%]
5[ 0.0%] 13[ 0.0%]
6[ 0.0%] 14[ 0.0%]
7[ 0.0%] 15[ 0.0%]
PID USER PRI NI S CPU CPU%▽MEM% TIME+ Command
1067 root RT 0 R 0 99.0 0.2 0:31.16 stress-ng-cpu [run]
975 arighi 20 0 R 0 1.0 0.0 0:26.32 yes
By allowing scx_bpf_reenqueue_local() to re-enqueue migration-disabled
tasks, the scheduler can choose to migrate them to other CPUs (CPU1 in
this case) via ops.enqueue(), leading to better CPU utilization:
0[||||||||||||||||||||||100.0%] 8[ 0.0%]
1[||||||||||||||||||||||100.0%] 9[ 0.0%]
2[ 0.0%] 10[ 0.0%]
3[ 0.0%] 11[ 0.0%]
4[ 0.0%] 12[ 0.0%]
5[ 0.0%] 13[ 0.0%]
6[ 0.0%] 14[ 0.0%]
7[ 0.0%] 15[ 0.0%]
PID USER PRI NI S CPU CPU%▽MEM% TIME+ Command
577 root RT 0 R 0 100.0 0.2 0:23.17 stress-ng-cpu [run]
555 arighi 20 0 R 1 100.0 0.0 0:28.67 yes
It's debatable whether per-CPU tasks should be re-enqueued as well, but
doing so is probably safer: the scheduler can recognize re-enqueued
tasks through the %SCX_ENQ_REENQ flag, reassess their placement, and
either put them back at the head of the local DSQ or let another task
attempt to take the CPU.
This also prevents giving per-CPU tasks an implicit priority boost,
which would otherwise make them more likely to reclaim CPUs preempted by
higher scheduling classes.
Fixes: 97e13ecb02 ("sched_ext: Skip per-CPU tasks in scx_bpf_reenqueue_local()")
Cc: stable@vger.kernel.org # v6.15+
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Acked-by: Changwoo Min <changwoo@igalia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
When printing the deprecation warning for scx_bpf_cpu_rq(), we may hit a
NULL pointer dereference if the kfunc is called before a BPF scheduler
is fully attached, for example, when invoked from a BPF timer or during
ops.init():
[ 50.752775] BUG: kernel NULL pointer dereference, address: 0000000000000331
...
[ 50.764205] RIP: 0010:scx_bpf_cpu_rq+0x30/0xa0
...
[ 50.787661] Call Trace:
[ 50.788398] <TASK>
[ 50.789061] bpf_prog_08f7fd2dcb187aaf_wakeup_timerfn+0x75/0x1a8
[ 50.792477] bpf_timer_cb+0x7e/0x140
[ 50.796003] hrtimer_run_softirq+0x91/0xe0
[ 50.796952] handle_softirqs+0xce/0x3c0
[ 50.799087] run_ksoftirqd+0x3e/0x70
[ 50.800197] smpboot_thread_fn+0x133/0x290
[ 50.802320] kthread+0x115/0x220
[ 50.804984] ret_from_fork+0x17a/0x1d0
[ 50.806920] ret_from_fork_asm+0x1a/0x30
[ 50.807799] </TASK>
Fix this by only printing the warning once the scheduler is fully
registered.
Fixes: 5c48d88fe0 ("sched_ext: deprecation warn for scx_bpf_cpu_rq()")
Cc: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_bpf_cpu_rq() works on an unlocked rq which generally isn't safe.
For the common use-cases scx_bpf_locked_rq() and
scx_bpf_cpu_curr() work, so add a deprecation warning
to scx_bpf_cpu_rq() so it can eventually be removed.
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Provide scx_bpf_cpu_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 <christian.loehle@arm.com>
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Most fields in scx_bpf_cpu_rq() assume that its rq_lock is held.
Furthermore they become meaningless without rq lock, too.
Make a safer version of scx_bpf_cpu_rq() that only returns a rq
if we hold rq lock of that rq.
Also mark the new scx_bpf_locked_rq() as returning NULL as
scx_bpf_cpu_rq() should've been too.
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
SCX hooks into CPU cgroup controller operations and read-locks
scx_cgroup_rwsem to exclude them while enabling and disable schedulers.
While this works, it's unnecessarily complicated given that
cgroup_[un]lock() are available and thus the cgroup operations can be locked
out that way.
Drop scx_cgroup_rwsem locking from the tg on/offline and cgroup [can_]attach
operations. Instead, grab cgroup_lock() from scx_cgroup_lock(). Drop
scx_cgroup_finish_attach() which is no longer necessary. Drop the now
unnecessary rcu locking and css ref bumping in scx_cgroup_init() and
scx_cgroup_exit().
As scx_cgroup_set_weight/bandwidth() paths aren't protected by
cgroup_lock(), rename scx_cgroup_rwsem to scx_cgroup_ops_rwsem and retain
the locking there.
This is overall simpler and will also allow enable/disable paths to
synchronize against cgroup changes independent of the CPU controller.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Acked-by: Andrea Righi <arighi@nvidia.com>
scx_sched.event_stats_cpu is the percpu counters that are used to track
stats. Introduce struct scx_sched_pcpu and move the counters inside. This
will ease adding more per-cpu fields. No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Andrea Righi <arighi@nvidia.com>
There currently isn't a place to place SCX-internal types and accessors to
be shared between ext.c and ext_idle.c. Create kernel/sched/ext_internal.h
and move internal type and accessor definitions there. This trims ext.c a
bit and makes future additions easier. Pure code reorganization. No
functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Andrea Righi <arighi@nvidia.com>
scx_enable() turns on the bypass mode while enable is in progress. If
enabling fails, it turns off the bypass mode and then triggers scx_error().
scx_error() will trigger scx_disable_workfn() which will turn on the bypass
mode again and unload the failed scheduler.
This moves the system out of bypass mode between the enable error path and
the disable path, which is unnecessary and can be brittle - e.g. the thread
running scx_enable() may already be on the failed scheduler and can be
switched out before it triggers scx_error() leading to a stall. The watchdog
would eventually kick in, so the situation isn't critical but is still
suboptimal.
There is nothing to be gained by turning off the bypass mode between
scx_enable() failure and scx_disable_workfn(). Keep bypass on.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Andrea Righi <arighi@nvidia.com>
During tasks iteration, the locks can be dropped using
scx_task_iter_unlock() to perform e.g. sleepable allocations. Afterwards,
scx_task_iter_relock() has to be called prior to other iteration operations,
which is error-prone. This can be easily automated by tracking whether
scx_tasks_lock is held in scx_task_iter and re-acquiring when necessary. It
already tracks whether the task's rq is locked after all.
- Add scx_task_iter->list_locked which remembers whether scx_tasks_lock is
held.
- Rename scx_task_iter->locked to scx_task_iter->locked_task to better
distinguish it from ->list_locked.
- Replace scx_task_iter_relock() with __scx_task_iter_maybe_relock() which
is automatically called by scx_task_iter_next() and scx_task_iter_stop().
- Drop explicit scx_task_iter_relock() calls.
The resulting behavior should be equivalent.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Andrea Righi <arighi@nvidia.com>
When enabling a sched_ext scheduler, we may trigger invalid task state
transitions, resulting in warnings like the following (which can be
easily reproduced by running the hotplug selftest in a loop):
sched_ext: Invalid task state transition 0 -> 3 for fish[770]
WARNING: CPU: 18 PID: 787 at kernel/sched/ext.c:3862 scx_set_task_state+0x7c/0xc0
...
RIP: 0010:scx_set_task_state+0x7c/0xc0
...
Call Trace:
<TASK>
scx_enable_task+0x11f/0x2e0
switching_to_scx+0x24/0x110
scx_enable.isra.0+0xd14/0x13d0
bpf_struct_ops_link_create+0x136/0x1a0
__sys_bpf+0x1edd/0x2c30
__x64_sys_bpf+0x21/0x30
do_syscall_64+0xbb/0x370
entry_SYSCALL_64_after_hwframe+0x77/0x7f
This happens because we skip initialization for tasks that are already
dead (with their usage counter set to zero), but we don't exclude them
during the scheduling class transition phase.
Fix this by also skipping dead tasks during class swiching, preventing
invalid task state transitions.
Fixes: a8532fac7b ("sched_ext: TASK_DEAD tasks must be switched into SCX on ops_enable")
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Pull sched_ext updates from Tejun Heo:
- Add support for cgroup "cpu.max" interface
- Code organization cleanup so that ext_idle.c doesn't depend on the
source-file-inclusion build method of sched/
- Drop UP paths in accordance with sched core changes
- Documentation and other misc changes
* tag 'sched_ext-for-6.17' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext:
sched_ext: Fix scx_bpf_reenqueue_local() reference
sched_ext: Drop kfuncs marked for removal in 6.15
sched_ext, rcu: Eject BPF scheduler on RCU CPU stall panic
kernel/sched/ext.c: fix typo "occured" -> "occurred" in comments
sched_ext: Add support for cgroup bandwidth control interface
sched_ext, sched/core: Factor out struct scx_task_group
sched_ext: Return NULL in llc_span
sched_ext: Always use SMP versions in kernel/sched/ext_idle.h
sched_ext: Always use SMP versions in kernel/sched/ext_idle.c
sched_ext: Always use SMP versions in kernel/sched/ext.h
sched_ext: Always use SMP versions in kernel/sched/ext.c
sched_ext: Documentation: Clarify time slice handling in task lifecycle
sched_ext: Make scx_locked_rq() inline
sched_ext: Make scx_rq_bypassing() inline
sched_ext: idle: Make local functions static in ext_idle.c
sched_ext: idle: Remove unnecessary ifdef in scx_bpf_cpu_node()
The comment mentions bpf_scx_reenqueue_local(), but the function
is provided for the BPF program implementing scx, as such the
naming convention is scx_bpf_reenqueue_local(), fix the comment.
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Avoid invoking update_locked_rq() when the runqueue (rq) pointer is NULL
in the SCX_CALL_OP and SCX_CALL_OP_RET macros.
Previously, calling update_locked_rq(NULL) with preemption enabled could
trigger the following warning:
BUG: using __this_cpu_write() in preemptible [00000000]
This happens because __this_cpu_write() is unsafe to use in preemptible
context.
rq is NULL when an ops invoked from an unlocked context. In such cases, we
don't need to store any rq, since the value should already be NULL
(unlocked). Ensure that update_locked_rq() is only called when rq is
non-NULL, preventing calling __this_cpu_write() on preemptible context.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Fixes: 18853ba782 ("sched_ext: Track currently locked rq")
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org # v6.15
sched_ext performed a kfunc renaming pass in 6.13 and kept the old names
around for compatibility with old binaries. These were scheduled for
cleanup in 6.15 but were missed. Submitting for cleanup in for-next.
Removed the kfuncs, their flags, and any references I could find to them
in doc comments. Left the entries in include/scx/compat.bpf.h as they're
still useful to make new binaries compatible with old kernels.
Tested by applying to my kernel. It builds and a modern version of
scx_lavd loads fine.
Signed-off-by: Jake Hillion <jake@hillion.co.uk>
Signed-off-by: Tejun Heo <tj@kernel.org>
For systems using a sched_ext scheduler and has panic_on_rcu_stall
enabled, try kicking out the current scheduler before issuing a panic.
While there are numerous reasons for RCU CPU stalls that are not
directly attributed to the scheduler, deferring the panic gives
sched_ext an opportunity to provide additional debug info when ejecting
the current scheduler. Also, handling the event more gracefully allows
us to potentially recover the system instead of incurring additional
down time.
Suggested-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: David Dai <david.dai@linux.dev>
Signed-off-by: Tejun Heo <tj@kernel.org>
From 077814f57f8acce13f91dc34bbd2b7e4911fbf25 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Fri, 13 Jun 2025 15:06:47 -1000
- Add CONFIG_GROUP_SCHED_BANDWIDTH which is selected by both
CONFIG_CFS_BANDWIDTH and EXT_GROUP_SCHED.
- Put bandwidth control interface files for both cgroup v1 and v2 under
CONFIG_GROUP_SCHED_BANDWIDTH.
- Update tg_bandwidth() to fetch configuration parameters from fair if
CONFIG_CFS_BANDWIDTH, SCX otherwise.
- Update tg_set_bandwidth() to update the parameters for both fair and SCX.
- Add bandwidth control parameters to struct scx_cgroup_init_args.
- Add sched_ext_ops.cgroup_set_bandwidth() which is invoked on bandwidth
control parameter updates.
- Update scx_qmap and maximal selftest to test the new feature.
Signed-off-by: Tejun Heo <tj@kernel.org>
More sched_ext fields will be added to struct task_group. In preparation,
factor out sched_ext fields into struct scx_task_group to reduce clutter in
the common header. No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Pull sched_ext/for-6.16-fixes to receive:
c50784e99f ("sched_ext: Make scx_group_set_weight() always update tg->scx.weight")
33796b9187 ("sched_ext, sched/core: Don't call scx_group_set_weight() prematurely from sched_create_group()")
which are needed to implement CPU bandwidth control interface support.
Signed-off-by: Tejun Heo <tj@kernel.org>
During task_group creation, sched_create_group() calls
scx_group_set_weight() with CGROUP_WEIGHT_DFL to initialize the sched_ext
portion. This is premature and ends up calling ops.cgroup_set_weight() with
an incorrect @cgrp before ops.cgroup_init() is called.
sched_create_group() should just initialize SCX related fields in the new
task_group. Fix it by factoring out scx_tg_init() from sched_init() and
making sched_create_group() call that function instead of
scx_group_set_weight().
v2: Retain CONFIG_EXT_GROUP_SCHED ifdef in sched_init() as removing it leads
to build failures on !CONFIG_GROUP_SCHED configs.
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 8195136669 ("sched_ext: Add cgroup support")
Cc: stable@vger.kernel.org # v6.12+
Otherwise, tg->scx.weight can go out of sync while scx_cgroup is not enabled
and ops.cgroup_init() may be called with a stale weight value.
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 8195136669 ("sched_ext: Add cgroup support")
Cc: stable@vger.kernel.org # v6.12+
Simplify the scheduler by making formerly SMP-only primitives and data
structures unconditional.
tj: Updated subject for clarity.
Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_locked_rq() is used both from ext.c and ext_idle.c, move it to ext.h
as a static inline function.
No functional changes.
v2: Rename locked_rq to scx_locked_rq_state, expose it and make
scx_locked_rq() inline, as suggested by Tejun.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
scx_rq_bypassing() is used both from ext.c and ext_idle.c, move it to
ext.h as a static inline function.
No functional changes.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
