Revert "sched_ext: Use rhashtable_lookup() instead of rhashtable_lookup_fast()"

This reverts commit c8191ee8e64a8c5c021a34e32868f2380965e82b which triggers
the following suspicious RCU usage warning:

[    6.647598] =============================
[    6.647603] WARNING: suspicious RCU usage
[    6.647605] 6.17.0-rc7-virtme #1 Not tainted
[    6.647608] -----------------------------
[    6.647608] ./include/linux/rhashtable.h:602 suspicious rcu_dereference_check() usage!
[    6.647610]
[    6.647610] other info that might help us debug this:
[    6.647610]
[    6.647612]
[    6.647612] rcu_scheduler_active = 2, debug_locks = 1
[    6.647613] 1 lock held by swapper/10/0:
[    6.647614]  #0: ffff8b14bbb3cc98 (&rq->__lock){-.-.}-{2:2}, at:
+raw_spin_rq_lock_nested+0x20/0x90
[    6.647630]
[    6.647630] stack backtrace:
[    6.647633] CPU: 10 UID: 0 PID: 0 Comm: swapper/10 Not tainted 6.17.0-rc7-virtme #1
+PREEMPT(full)
[    6.647643] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[    6.647646] Sched_ext: beerland_1.0.2_g27d63fc3_x86_64_unknown_linux_gnu (enabled+all)
[    6.647648] Call Trace:
[    6.647652]  <IRQ>
[    6.647655]  dump_stack_lvl+0x78/0xe0
[    6.647665]  lockdep_rcu_suspicious+0x14a/0x1b0
[    6.647672]  __rhashtable_lookup.constprop.0+0x1d5/0x250
[    6.647680]  find_dsq_for_dispatch+0xbc/0x190
[    6.647684]  do_enqueue_task+0x25b/0x550
[    6.647689]  enqueue_task_scx+0x21d/0x360
[    6.647692]  ? trace_lock_acquire+0x22/0xb0
[    6.647695]  enqueue_task+0x2e/0xd0
[    6.647698]  ttwu_do_activate+0xa2/0x290
[    6.647703]  sched_ttwu_pending+0xfd/0x250
[    6.647706]  __flush_smp_call_function_queue+0x1cd/0x610
[    6.647714]  __sysvec_call_function_single+0x34/0x150
[    6.647720]  sysvec_call_function_single+0x6e/0x80
[    6.647726]  </IRQ>
[    6.647726]  <TASK>
[    6.647727]  asm_sysvec_call_function_single+0x1a/0x20

Reported-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 99a5f6429207dcff857ff227fc640111c6b25157..2b0e88206d0768634ab7014fb037f7860c04ca5b 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -189,7 +189,7 @@ static struct scx_dispatch_q *find_global_dsq(struct scx_sched *sch,
 
 static struct scx_dispatch_q *find_user_dsq(struct scx_sched *sch, u64 dsq_id)
 {
-       return rhashtable_lookup(&sch->dsq_hash, &dsq_id, dsq_hash_params);
+       return rhashtable_lookup_fast(&sch->dsq_hash, &dsq_id, dsq_hash_params);
 }
 
 /*