Re: [PATCH -next] ipc: use GFP_ATOMIC under spin lock

[Matthew Wilcox]

On Tue, Apr 28, 2020 at 03:47:36AM +0000, Wei Yongjun wrote:
> The function ipc_id_alloc() is called from ipc_addid(), in which
> a spin lock is held, so we should use GFP_ATOMIC instead.
> 
> Fixes: de5738d1c364 ("ipc: convert ipcs_idr to XArray")
> Signed-off-by: Wei Yongjun <weiyongjun1@xxxxxxxxxx>

I see why you think that, but it's not true.  Yes, we hold a spinlock, but
the spinlock is in an object which is not reachable from any other CPU.
So it's not possible to deadlock.  This probably confuses all kinds
of automated checkers, and I should probably rewrite the code to not
acquire the new spinlock until we're already holding the xa_lock.

Converting to GFP_ATOMIC is completely wrong.