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Peter Zijlstra
bca4104b00
Kent reported an occasional KASAN splat in lockdep. Mark then noted:
> I suspect the dodgy access is to chain_block_buckets[-1], which hits the last 4
> bytes of the redzone and gets (incorrectly/misleadingly) attributed to
> nr_large_chain_blocks.
That would mean @size == 0, at which point size_to_bucket() returns -1
and the above happens.
alloc_chain_hlocks() has 'size - req', for the first with the
precondition 'size >= rq', which allows the 0.
This code is trying to split a block, del_chain_block() takes what we
need, and add_chain_block() puts back the remainder, except in the
above case the remainder is 0 sized and things go sideways.
Fixes: 810507fe6f ("locking/lockdep: Reuse freed chain_hlocks entries")
Reported-by: Kent Overstreet <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Kent Overstreet <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]