Commit 5944ce092b97 ("arch_topology: Build cacheinfo from primary CPU") adds functionality that architectures can use to optionally allocate and build cacheinfo early during boot. Commit 6539cffa9495 ("cacheinfo: Add arch specific early level initializer") lets secondary CPUs correct (and reallocate memory) cacheinfo data if needed.
If the early build functionality is not used and cacheinfo does not need correction, memory for cacheinfo is never allocated. x86 does not use the early build functionality. Consequently, during the cacheinfo CPU hotplug callback, last_level_cache_is_valid() attempts to dereference a NULL pointer:
BUG: kernel NULL pointer dereference, address: 0000000000000100 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not present page PGD 0 P4D 0 Oops: 0000 [#1] PREEPMT SMP NOPTI CPU: 0 PID 19 Comm: cpuhp/0 Not tainted 6.4.0-rc2 #1 RIP: 0010: last_level_cache_is_valid+0x95/0xe0a
Allocate memory for cacheinfo during the cacheinfo CPU hotplug callback if not done earlier.
Cc: Andreas Herrmann aherrmann@suse.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Chen Yu yu.c.chen@intel.com Cc: Huang Ying ying.huang@intel.com Cc: Len Brown len.brown@intel.com Cc: Radu Rendec rrendec@redhat.com Cc: Pierre Gondois Pierre.Gondois@arm.com Cc: Pu Wen puwen@hygon.cn Cc: "Rafael J. Wysocki" rafael.j.wysocki@intel.com Cc: Sudeep Holla sudeep.holla@arm.com Cc: Srinivas Pandruvada srinivas.pandruvada@linux.intel.com Cc: Will Deacon will@kernel.org Cc: Zhang Rui rui.zhang@intel.com Cc: linux-arm-kernel@lists.infradead.org Cc: stable@vger.kernel.org Reviewed-by: Radu Rendec rrendec@redhat.com Reviewed-by: Sudeep Holla sudeep.holla@arm.com Fixes: 6539cffa9495 ("cacheinfo: Add arch specific early level initializer") Signed-off-by: Ricardo Neri ricardo.neri-calderon@linux.intel.com --- The motivation for commit 5944ce092b97 was to prevent a BUG splat in PREEMPT_RT kernels during memory allocation. This splat is not observed on x86 because the memory allocation for cacheinfo happens in detect_cache_attributes() from the cacheinfo CPU hotplug callback.
The dereference of a NULL pointer is not observed today because cache_leaves(cpu) is zero until after init_cache_level() is called (also during the CPU hotplug callback). A subsequent changeset will set the number of cache leaves earlier and the NULL-pointer dereference will be observed. --- Changes since v3: * Added Reviewed-by tag from Radu and Sudeep. Thanks!
Changes since v2: * Introduced this patch.
Changes since v1: * N/A --- drivers/base/cacheinfo.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c index 967c5cf3fb1d..735ccead190e 100644 --- a/drivers/base/cacheinfo.c +++ b/drivers/base/cacheinfo.c @@ -557,7 +557,11 @@ static inline int init_level_allocate_ci(unsigned int cpu) */ ci_cacheinfo(cpu)->early_ci_levels = false;
- if (cache_leaves(cpu) <= early_leaves) + /* + * Some architectures (e.g., x86) do not use early initialization. + * Allocate memory now in such case. + */ + if (cache_leaves(cpu) <= early_leaves && per_cpu_cacheinfo(cpu)) return 0;
kfree(per_cpu_cacheinfo(cpu));