__csd_lock_record() publishes per-CPU CSD debug state that is read by csd_lock_wait_toolong() on another CPU. The remote side first reads cur_csd with smp_load_acquire() and, when non-NULL, may then read the matching cur_csd_func and cur_csd_info fields.
Use smp_store_release() when publishing cur_csd so that the preceding cur_csd_func and cur_csd_info stores are ordered before the pointer that csd_lock_wait_toolong() acquires. This replaces the open-coded smp_wmb() plus plain cur_csd store with the release operation that matches the smp_load_acquire() in csd_lock_wait_toolong(). For the clear path, use smp_store_release(&cur_csd, NULL) so that clearing the diagnostic state remains ordered after the preceding callback/unlock work, without requiring a full barrier before the store. On x86 this removes the locked full barrier from the clear path; on weaker memory models it uses the release operation needed by the smp_load_acquire() in csd_lock_wait_toolong(). The old code also had smp_mb() calls around cur_csd updates. Those would only be needed if cur_csd were treated as an exact live-state marker whose publication had to be observed before callback execution or CSD unlock. CSD stall warnings do not currently have RCU-style stall-ended checks, so they already allow the stall to end while diagnostics are being assembled. The cur_csd record is therefore best-effort diagnostic context, not a precise completion/stall boundary. Signed-off-by: Usama Arif <[email protected]> --- kernel/smp.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/kernel/smp.c b/kernel/smp.c index a0bb56bd8dda..5ba4a20ba77d 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -182,16 +182,12 @@ static atomic_t csd_bug_count = ATOMIC_INIT(0); static void __csd_lock_record(call_single_data_t *csd) { if (!csd) { - smp_mb(); /* NULL cur_csd after unlock. */ - __this_cpu_write(cur_csd, NULL); + smp_store_release(this_cpu_ptr(&cur_csd), NULL); return; } __this_cpu_write(cur_csd_func, csd->func); __this_cpu_write(cur_csd_info, csd->info); - smp_wmb(); /* func and info before csd. */ - __this_cpu_write(cur_csd, csd); - smp_mb(); /* Update cur_csd before function call. */ - /* Or before unlock, as the case may be. */ + smp_store_release(this_cpu_ptr(&cur_csd), csd); } static __always_inline void csd_lock_record(call_single_data_t *csd) -- 2.53.0-Meta
