Re: [PATCH 1/2] lockdep: Avoid to modify chain keys in validate_chain()

[Peter Zijlstra]

On Mon, Nov 02, 2020 at 01:37:41PM +0800, Boqun Feng wrote:
> Chris Wilson reported a problem spotted by check_chain_key(): a chain
> key got changed in validate_chain() because we modify the ->read in
> validate_chain() to skip checks for dependency adding, and ->read is
> taken into calculation for chain key since commit f611e8cf98ec
> ("lockdep: Take read/write status in consideration when generate
> chainkey").
> 
> Fix this by avoiding to modify ->read in validate_chain() based on two
> facts: a) since we now support recursive read lock detection, there is
> no need to skip checks for dependency adding for recursive readers, b)
> since we have a), there is only one case left (nest_lock) where we want
> to skip checks in validate_chain(), we simply remove the modification
> for ->read and rely on the return value of check_deadlock() to skip the
> dependency adding.
> 
> Reported-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

Thanks Boqun!