Re: [PATCH] Revert "locking/mutex: Complain upon mutex API misuse in IRQ contexts"

[David Howells]

Davidlohr Bueso <dave@xxxxxxxxxxxx> wrote:

> This ended up causing some noise in places such as rxrpc running in softirq.
> 
> The warning is misleading in this case as the mutex trylock and unlock
> operations are done within the same context; and therefore we need not
> worry about the PI-boosting issues that comes along with no single-owner
> lock guarantees.
> 
> While we don't want to support this in mutexes, there is no way out of
> this yet; so lets get rid of the WARNs for now, as it is only fair to
> code that has historically relied on non-preemptible softirq guarantees.
> In addition, changing the lock type is also unviable: exclusive rwsems
> have the same issue (just not the WARN_ON) and counting semaphores
> would introduce a performance hit as mutexes are a lot more optimized.
> 
> This reverts commit 5d4ebaa87329ef226e74e52c80ac1c62e4948987.
> 
> Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>

Tested-by: David Howells <dhowells@xxxxxxxxxx>