bpf: Add open coded version of kmem_cache iterator

Add a new open coded iterator for kmem_cache which can be called from a
BPF program like below. It doesn't take any argument and traverses all
kme

bpf: Add open coded version of kmem_cache iterator

Add a new open coded iterator for kmem_cache which can be called from a
BPF program like below. It doesn't take any argument and traverses all
kmem_cache entries.

struct kmem_cache *pos;

bpf_for_each(kmem_cache, pos) {
...
}

As it needs to grab slab_mutex, it should be called from sleepable BPF
programs only.

Also update the existing iterator code to use the open coded version
internally as suggested by Andrii.

Signed-off-by: Namhyung Kim <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

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bpf: Add kmem_cache iterator

The new "kmem_cache" iterator will traverse the list of slab caches
and call attached BPF programs for each entry. It should check the
argument (ctx.s) if it's NULL bef

bpf: Add kmem_cache iterator

The new "kmem_cache" iterator will traverse the list of slab caches
and call attached BPF programs for each entry. It should check the
argument (ctx.s) if it's NULL before using it.

Now the iteration grabs the slab_mutex only if it traverse the list and
releases the mutex when it runs the BPF program. The kmem_cache entry
is protected by a refcount during the execution.

Signed-off-by: Namhyung Kim <[email protected]>
Acked-by: Vlastimil Babka <[email protected]> #slab
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

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