[xen stable-4.18] xen/sched: set all sched_resource data inside locked region for new cpu

[patchbot@xxxxxxx]

commit 3999b675cad5b717274d6493899b0eea8896f4d7
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Tue May 21 10:24:26 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue May 21 10:24:26 2024 +0200

    xen/sched: set all sched_resource data inside locked region for new cpu
    
    When adding a cpu to a scheduler, set all data items of struct
    sched_resource inside the locked region, as otherwise a race might
    happen (e.g. when trying to access the cpupool of the cpu):
    
      (XEN) ----[ Xen-4.19.0-1-d  x86_64  debug=y  Tainted:     H  ]----
      (XEN) CPU:    45
      (XEN) RIP:    e008:[<ffff82d040244cbf>] 
common/sched/credit.c#csched_load_balance+0x41/0x877
      (XEN) RFLAGS: 0000000000010092   CONTEXT: hypervisor
      (XEN) rax: ffff82d040981618   rbx: ffff82d040981618   rcx: 
0000000000000000
      (XEN) rdx: 0000003ff68cd000   rsi: 000000000000002d   rdi: 
ffff83103723d450
      (XEN) rbp: ffff83207caa7d48   rsp: ffff83207caa7b98   r8:  
0000000000000000
      (XEN) r9:  ffff831037253cf0   r10: ffff83103767c3f0   r11: 
0000000000000009
      (XEN) r12: ffff831037237990   r13: ffff831037237990   r14: 
ffff831037253720
      (XEN) r15: 0000000000000000   cr0: 000000008005003b   cr4: 
0000000000f526e0
      (XEN) cr3: 000000005bc2f000   cr2: 0000000000000010
      (XEN) fsb: 0000000000000000   gsb: 0000000000000000   gss: 
0000000000000000
      (XEN) ds: 0000   es: 0000   fs: 0000   gs: 0000   ss: 0000   cs: e008
      (XEN) Xen code around <ffff82d040244cbf> 
(common/sched/credit.c#csched_load_balance+0x41/0x877):
      (XEN)  48 8b 0c 10 48 8b 49 08 <48> 8b 79 10 48 89 bd b8 fe ff ff 49 8b 
4e 28 48
      <snip>
      (XEN) Xen call trace:
      (XEN)    [<ffff82d040244cbf>] R 
common/sched/credit.c#csched_load_balance+0x41/0x877
      (XEN)    [<ffff82d040245a18>] F 
common/sched/credit.c#csched_schedule+0x36a/0x69f
      (XEN)    [<ffff82d040252644>] F common/sched/core.c#do_schedule+0xe8/0x433
      (XEN)    [<ffff82d0402572dd>] F common/sched/core.c#schedule+0x2e5/0x2f9
      (XEN)    [<ffff82d040232f35>] F common/softirq.c#__do_softirq+0x94/0xbe
      (XEN)    [<ffff82d040232fc8>] F do_softirq+0x13/0x15
      (XEN)    [<ffff82d0403075ef>] F arch/x86/domain.c#idle_loop+0x92/0xe6
      (XEN)
      (XEN) Pagetable walk from 0000000000000010:
      (XEN)  L4[0x000] = 000000103ff61063 ffffffffffffffff
      (XEN)  L3[0x000] = 000000103ff60063 ffffffffffffffff
      (XEN)  L2[0x000] = 0000001033dff063 ffffffffffffffff
      (XEN)  L1[0x000] = 0000000000000000 ffffffffffffffff
      (XEN)
      (XEN) ****************************************
      (XEN) Panic on CPU 45:
      (XEN) FATAL PAGE FAULT
      (XEN) [error_code=0000]
      (XEN) Faulting linear address: 0000000000000010
      (XEN) ****************************************
    
    Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Fixes: a8c6c623192e ("sched: clarify use cases of schedule_cpu_switch()")
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Tested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: d104a07524ffc92ae7a70dfe192c291de2a563cc
    master date: 2024-05-15 19:59:52 +0100
---
 xen/common/sched/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
index 34ad39b9ad..3c2403ebcf 100644
--- a/xen/common/sched/core.c
+++ b/xen/common/sched/core.c
@@ -3179,6 +3179,8 @@ int schedule_cpu_add(unsigned int cpu, struct cpupool *c)
 
     sr->scheduler = new_ops;
     sr->sched_priv = ppriv;
+    sr->granularity = cpupool_get_granularity(c);
+    sr->cpupool = c;
 
     /*
      * Reroute the lock to the per pCPU lock as /last/ thing. In fact,
@@ -3191,8 +3193,6 @@ int schedule_cpu_add(unsigned int cpu, struct cpupool *c)
     /* _Not_ pcpu_schedule_unlock(): schedule_lock has changed! */
     spin_unlock_irqrestore(old_lock, flags);
 
-    sr->granularity = cpupool_get_granularity(c);
-    sr->cpupool = c;
     /* The  cpu is added to a pool, trigger it to go pick up some work */
     cpu_raise_softirq(cpu, SCHEDULE_SOFTIRQ);
 
--
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