On Thu, 2017-12-07 at 17:23:27 UTC, Anju T Sudhakar wrote:

imc_common_cpuhp_mem_free() is the common function for all IMC (In-memory
Collection counters) domains to unregister cpuhotplug callback and free memory.
Since kfree of memory allocated for nest-imc (per_nest_pmu_arr) is in the common
code, all domains (core/nest/thread) can do the kfree in the failure case.

This could potentially create a call trace as shown below, where core(/thread/nest)
imc pmu initialization fails and in the failure path imc_common_cpuhp_mem_free()
free the memory(per_nest_pmu_arr), which is allocated by successfully registered
nest units.


The call trace is generated in a scenario where core-imc initialization is
made to fail and a cpuhotplug is performed in a p9 system.
During cpuhotplug ppc_nest_imc_cpu_offline() tries to access per_nest_pmu_arr,
which is already freed by core-imc.

[  136.563618] NIP [c000000000cb6a94] mutex_lock+0x34/0x90
[  136.563653] LR [c000000000cb6a88] mutex_lock+0x28/0x90
[  136.563687] Call Trace:
[  136.563707] [c0000016b7a93b90] [c000000000cb6a88] mutex_lock+0x28/0x90 (unreliable)
[  136.563762] [c0000016b7a93bc0] [c0000000002bc720] perf_pmu_migrate_context+0x90/0x3a0
[  136.563814] [c0000016b7a93c60] [c0000000000f7a40] ppc_nest_imc_cpu_offline+0x190/0x1f0
[  136.563867] [c0000016b7a93cb0] [c000000000108140] cpuhp_invoke_callback+0x160/0x820
[  136.563918] [c0000016b7a93d30] [c00000000010939c] cpuhp_thread_fun+0x1bc/0x270
[  136.563970] [c0000016b7a93d60] [c00000000013d2b0] smpboot_thread_fn+0x250/0x290
[  136.564022] [c0000016b7a93dc0] [c000000000136f18] kthread+0x1a8/0x1b0
[  136.564067] [c0000016b7a93e30] [c00000000000b4e8] ret_from_kernel_thread+0x5c/0x74

To address this scenario do the kfree(per_nest_pmu_arr) only in case of
nest-imc initialization failure, and when there is no other nest units registered.


Fixes: 73ce9aec65b1 ("powerpc/perf: Fix IMC_MAX_PMU macro")
Signed-off-by: Anju T Sudhakar <redacted>
Reviewed-by: Madhavan Srinivasan <redacted>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/110df8bd3e418b3476cae80babe8ad

cheers