From mboxrd@z Thu Jan 1 00:00:00 1970 From: mingo@kernel.org (Ingo Molnar) Date: Tue, 24 Jul 2018 09:15:18 +0200 Subject: [PATCHv4 01/12] atomic/tty: Fix up atomic abuse in ldsem In-Reply-To: <20180716113017.3909-2-mark.rutland@arm.com> References: <20180716113017.3909-1-mark.rutland@arm.com> <20180716113017.3909-2-mark.rutland@arm.com> Message-ID: <20180724071518.GA7300@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org * Mark Rutland wrote: > From: Peter Zijlstra > > Mark found ldsem_cmpxchg() needed an (atomic_long_t *) cast to keep > working after making the atomic_long interface type safe. > > Needing casts is bad form, which made me look at the code. There are no > ld_semaphore::count users outside of these functions so there is no > reason why it can not be an atomic_long_t in the first place, obviating > the need for this cast. > > That also ensures the loads use atomic_long_read(), which implies (at > least) READ_ONCE() in order to guarantee single-copy-atomic loads. > > When using atomic_long_try_cmpxchg() the ldsem_cmpxchg() wrapper gets > very thin (the only difference is not changing *old on success, which > most callers don't seem to care about). > > So rework the whole thing to use atomic_long_t and its accessors > directly. > > While there, fixup all the horrible comment styles. > > Cc: Peter Hurley > Acked-by: Will Deacon > Reported-by: Mark Rutland > Reviewed-by: Andy Shevchenko > Signed-off-by: Peter Zijlstra (Intel) > Signed-off-by: Mark Rutland > Cc: Ingo Molnar > --- > drivers/tty/tty_ldsem.c | 82 ++++++++++++++++++++--------------------------- > include/linux/tty_ldisc.h | 4 +-- > 2 files changed, 37 insertions(+), 49 deletions(-) > > Note: Greg has queued this via the in the tty tree for v4.19, which can be seen at: > > https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git/commit/?h=tty-next&id=5fd691afdf929061c391d897fa627822c3b2fd5a Can this patch be skipped, or do the others depend on it? Thanks, Ingo