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3541a2b06e
kmemleak_scan() can run for ages on large debug kernels. It was
causing some soft-lockups which I got fixed with commit
3175fcfec8b16baeb ("mm/kmemleak: avoid soft lockup when scanning task
stacks") with our beloved cond_resched().
I've got the fix above deployed in the Meta fleet, and now I am seeing:
INFO: rcu_tasks detected stalls on tasks:
task:kmemleak state:R ... nvcsw: 274/274 holdout: 1 idle_cpu: -1/3
scan_block
scan_gray_list
kmemleak_scan
and, worse, blocks the callers waiting on that grace period. Here a BPF
struct_ops map free, which waits via synchronize_rcu_mult(call_rcu,
call_rcu_tasks), is stuck long enough to also trip the hung task check:
INFO: task kworker/...:bpf_map_free_deferred blocked for 122 seconds
__wait_rcu_gp
bpf_struct_ops_map_free
Then I've learned that cond_resched() is not an RCU-tasks quiescent
state, so, we need to use stronger primitives.
Use cond_resched_tasks_rcu_qs() at the scan reschedule points so the scan
reports an RCU-tasks quiescent state as it proceeds.
Inspired by commit b96285e10a ("tracing: Have osnoise_main() add a
quiescent state for task rcu").
Link: https://lore.kernel.org/20260720-kmemleak_rcu_task-v1-1-5b460ade777d@debian.org
Fixes: c4b28963fd ("mm/kmemleak: rely on rcu for task stack scanning")
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: SJ Park <sj@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Puranjay Mohan <puranjay@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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