In the Linux kernel, the following vulnerability has been resolved:
regulator: core: regulator_lock_two() should test for EDEADLK not EDEADLOCK
Compare against -EDEADLK, which is what ww_mutex_lock() actually returns and what every other deadlock check in this file already uses.
Function regulator_lock_two() acquires two regulators via regulator_lock_nested() -> ww_mutex_lock(). On contention, ww_mutex_lock() returns -EDEADLK, which is the caller's signal to drop the lock it holds and retry the acquisition in the canonical order.
However, regulator_lock_two() tests the return value against -EDEADLOCK rather than -EDEADLK. On most architectures, EDEADLK and EDEADLOCK are the same value, so the comparison happens to be correct and the bug is invisible. But on MIPS, SPARC, and PowerPC, those two errors have different values. The test is wrong: a genuine -EDEADLK backoff no longer matches -EDEADLOCK, so instead of unlocking and retrying, the code falls into WARN_ON(ret) and returns with only one of the two regulators locked.
In practice, this is a bug only on MIPS, because the regulator core is not built or used on the other two platforms.
In general, EDEADLK is preferred over EDEADLOCK for new code.