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- SMP-call fixes when CSD lock debugging is enabled (Chuyi Zhou)

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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'smp-urgent-2026-07-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull SMP debug fixes from Ingo Molnar:

 - SMP-call fixes when CSD lock debugging is enabled (Chuyi Zhou)

* tag 'smp-urgent-2026-07-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  smp: Make CSD lock acquisition atomic for debug mode
  smp: Avoid invalid per-CPU CSD lookup with CSD lock debug
This commit is contained in:
Linus Torvalds 2026-07-26 08:47:01 -07:00
commit a6671109d6
1 changed files with 25 additions and 5 deletions
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30
kernel/smp.c
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@ -137,10 +137,10 @@ csd_do_func(smp_call_func_t func, void *info, call_single_data_t *csd)
trace_csd_function_exit(func, csd);
}
#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
static DEFINE_STATIC_KEY_MAYBE(CONFIG_CSD_LOCK_WAIT_DEBUG_DEFAULT, csdlock_debug_enabled);
#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
/*
* Parse the csdlock_debug= kernel boot parameter.
*
@ -342,6 +342,10 @@ static __always_inline void csd_lock_wait(call_single_data_t *csd)
smp_cond_load_acquire(&csd->node.u_flags, !(VAL & CSD_FLAG_LOCK));
}
#else
static __always_inline void __csd_lock_wait(call_single_data_t *csd)
{
}
static void csd_lock_record(call_single_data_t *csd)
{
}
@ -354,8 +358,23 @@ static __always_inline void csd_lock_wait(call_single_data_t *csd)
static __always_inline void csd_lock(call_single_data_t *csd)
{
csd_lock_wait(csd);
csd->node.u_flags |= CSD_FLAG_LOCK;
if (IS_ENABLED(CONFIG_CSD_LOCK_WAIT_DEBUG) &&
static_branch_unlikely(&csdlock_debug_enabled)) {
for (;;) {
unsigned int flags;
__csd_lock_wait(csd);
flags = READ_ONCE(csd->node.u_flags);
if (!(flags & CSD_FLAG_LOCK) &&
try_cmpxchg_acquire(&csd->node.u_flags, &flags, flags | CSD_FLAG_LOCK))
break;
}
} else {
csd_lock_wait(csd);
csd->node.u_flags |= CSD_FLAG_LOCK;
}
/*
* prevent CPU from reordering the above assignment
@ -380,7 +399,8 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(call_single_data_t, csd_data);
#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
static call_single_data_t *get_single_csd_data(int cpu)
{
if (static_branch_unlikely(&csdlock_debug_enabled))
if (static_branch_unlikely(&csdlock_debug_enabled) &&
(unsigned int)cpu < nr_cpu_ids)
return per_cpu_ptr(&csd_data, cpu);
return this_cpu_ptr(&csd_data);
}