From: Chuyi Zhou Date: Thu, 16 Jul 2026 00:45:38 +0000 (-0700) Subject: smp: Avoid invalid per-CPU CSD lookup with CSD lock debug X-Git-Tag: v7.2-rc5~11^2~1 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c58ea9adf7342508c6ac0b7ad79ef10d589f9c6e;p=thirdparty%2Flinux.git smp: Avoid invalid per-CPU CSD lookup with CSD lock debug Commit b0473dcd4b1d ("smp: Improve smp_call_function_single() CSD-lock diagnostics") made smp_call_function_single() use the destination CPU's csd_data when CSD lock debugging is enabled. That lets the debug code associate a stuck CSD lock with the target CPU, but it also means the CPU argument is used in per_cpu_ptr() before generic_exec_single() has a chance to validate it. This becomes unsafe when smp_call_function_any() cannot find an online CPU in the supplied mask. In that case the selected CPU can be nr_cpu_ids, and the !wait path calls get_single_csd_data(cpu) before generic_exec_single() returns -ENXIO. With csdlock_debug_enabled set, that indexes the per-CPU offset array with an invalid CPU number. Use the destination CPU's csd_data only when the CPU number is within nr_cpu_ids. For invalid CPU numbers, fall back to the local CPU's csd_data and let generic_exec_single() perform the existing validation and return -ENXIO. Fixes: b0473dcd4b1d ("smp: Improve smp_call_function_single() CSD-lock diagnostics") Signed-off-by: Chuyi Zhou Signed-off-by: Paul E. McKenney Signed-off-by: Thomas Gleixner Reviewed-by: Paul E. McKenney Acked-by: Muchun Song Link: https://patch.msgid.link/20260716004539.13983-1-paulmck@kernel.org --- diff --git a/kernel/smp.c b/kernel/smp.c index a0bb56bd8dda..dc6582bb35d0 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -380,7 +380,8 @@ 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); }