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Since kmalloc_nolock() always fails in NMI and hardirq contexts on
PREEMPT_RT, slub_kunit cannot properly test _nolock() APIs.
Register a kprobe pre-handler to invoke kmalloc_nolock() and
kfree_nolock() in the middle of the slab allocator. However, do not
register the handler on UP kernels because that use case is not
well supported [1] in the kernel.
To attach the pre-handler while s->cpu_sheaves->lock or n->list_lock
is held, add a wrapper function for lockdep_assert_held() that calls
a no-op function slab_attach_kprobe_locked() on debug builds. The
function is optimized away when neither CONFIG_PROVE_LOCKING nor
CONFIG_DEBUG_VM is selected and register_kprobe() fails.
The function calls barrier() to prevent the compiler from optimizing
away its callsites. Otherwise, the compiler may consider the function
does not have any side effect and remove callsites.
Compared to using plain kprobe, this has two advantages: 1) it avoids
hardcoding function names in the test, and 2) it can trigger those APIs
in the middle of a function, where the lock is expected to be held as
annotated with lockdep.
While it was proposed [2] to use kunit function redirection to test
this, it is currently infeasible as some lock helpers don't have
symbols.
Factor out the nested loop that calls kmalloc and friends to
test_kmalloc_kfree(), and call them in
test_kmalloc_kfree_nolock_{perf,kprobe}(), each being an independent
test case. During the refactoring, drop alloc_fail handling as it
doesn't provide much benefits.
Link: https://lore.kernel.org/linux-mm/20260427-nolock-api-fix-v2-0-a6b83a92d9a4@kernel.org [1]
Link: https://lore.kernel.org/linux-mm/6edebc2b-5f5a-4b9c-9a4c-564310acee1b@kernel.org [2]
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Shengming Hu <hu.shengming@zte.com.cn>
Signed-off-by: Harry Yoo (Oracle) <harry@kernel.org>
Link: https://patch.msgid.link/20260729-kfree_rcu_nolock-v5-1-a28cdcda9673@kernel.org
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
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