Re: [PATCH v2 00/10] rcu: Improve callback diagnostics and validation

[Joel Fernandes]

On Tue, Oct 27, 2026 at 03:09:13PM +0800, Kunwu Chan wrote:
> Hi,
> 
> This series improves callback diagnostics and validation across RCU,
> SRCU, and RCU Tasks.
> 
> Patches 1-3 record callback registration stacks for KASAN in Tree
> SRCU, Tiny SRCU, and Tiny RCU.  KASAN prints the recorded auxiliary
> stack when reporting a use-after-free.
> 
> Patches 4-6 add rcu_head alignment and NULL callback-function checks.
> 
> Patches 7-10 detect duplicate callback enqueue attempts before
> queueing, using the RCU head debug-object mechanism.  A duplicate
> registration is rejected at entry and __ratelimit() controls the
> diagnostic output group (pr_err, mem_dump_obj, dump_stack).
> Detection requires CONFIG_DEBUG_OBJECTS_RCU_HEAD.
> 
> Changes since v1:
> - Patches 7-9: __ratelimit() + dump_stack() instead of hard-coded limit
> - Patch 10 (new): same change for Tree RCU's rcu_do_enqueue()
> - Patch 9: fixed log format to avoid pseudo-function names
> - Tags: Reviewed-by (4-6), Suggested-by (7-10)
> - v1: https://lore.kernel.org/all/20261023101841.2910719-1-kunwu.chan@xxxxxxxxx/
> 
> 
> Testing:
>   rcutorture with KASAN (SRCU-N, SRCU-P, SRCU-T, SRCU-U, TINY01,
>   TINY02, TREE03, 3min each): all exitcode 0.
> 
>   KASAN aux stack (QEMU, CONFIG_KASAN_GENERIC=y):
>     Last potentially related work creation:
>      kasan_save_stack+0x33/0x60
>      kasan_record_aux_stack+0x8c/0xa0
>      call_srcu+0xb2/0x390
> 
>   Duplicate enqueue (QEMU, CONFIG_DEBUG_OBJECTS_RCU_HEAD=y):
>     call_srcu(): Duplicate call_srcu() CB ... ->cb
>     dump_stack_lvl+0x47/0x60
>     call_rcu_tasks_generic(): Duplicate CB for RCU Tasks, ... ->cb
>     dump_stack_lvl+0x47/0x60
>     rcu_do_enqueue(): Double-freed CB ... ->cb  slab kmalloc-16 ...
> 
> 
> Kunwu Chan (10):
>   srcu: Record callback registration stack for KASAN
>   srcutiny: Record callback registration stack for KASAN
>   rcu: Record callback registration stack for Tiny RCU
>   srcu: Validate callback arguments
>   rcu: Validate callback arguments in Tiny RCU
>   rcu-tasks: Validate callback arguments
>   srcu: Detect duplicate callback enqueue at registration
>   srcutiny: Detect duplicate callback enqueue
>   rcu-tasks: Detect duplicate callback enqueue
>   rcu: Improve duplicate callback diagnostics


Reviewed-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>

All look good to me, applying for further testing and review for 7.5. Did you
also test double-call-srcu and confirm intended behavior? Thanks!

thanks,

Joel Fernandes


> 
>  kernel/rcu/srcutiny.c | 34 ++++++++++++++++++++++++++++++++++
>  kernel/rcu/srcutree.c | 36 ++++++++++++++++++++++++++++++------
>  kernel/rcu/tasks.h    | 27 +++++++++++++++++++++++++++
>  kernel/rcu/tiny.c     | 11 +++++++++++
>  kernel/rcu/tree.c     |  9 +++++++--
>  5 files changed, 109 insertions(+), 8 deletions(-)
> 
> 
> base-commit: 940793b926aa94bf65ec404043050888e3053188
> -- 
> 2.43.0
>