From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@arm.linux.org.uk (Russell King - ARM Linux) Date: Wed, 27 Mar 2013 22:56:10 +0000 Subject: [PATCH v4] clk: allow reentrant calls into the clk framework In-Reply-To: <1364368183-24420-1-git-send-email-mturquette@linaro.org> References: <1364368183-24420-1-git-send-email-mturquette@linaro.org> Message-ID: <20130327225610.GR4977@n2100.arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Mar 27, 2013 at 12:09:43AM -0700, Mike Turquette wrote: > + /* set context for any reentrant calls */ > + atomic_set(&prepare_context, (int) get_current()); ... > + if (mutex_is_locked(&prepare_lock)) > + if ((void *) atomic_read(&prepare_context) == get_current()) > + return true; If you really want to do it like this, then the _correct_ way to do it is: if (atomic_read(&prepare_context) == (int)get_current()) So that any effects from the cast are the same in both parts. Otherwise, you will be running into the possibility that a cast could do something like truncate the returned value, resulting in the test condition using pointers always being false. It's not that much of a problem on ARM, but it's a matter of good programming discpline that such issues are avoided. Even better would be to cast it to unsigned long - this is the value which the atomic types use, and that is less likely to be truncated. It also helps to avoid the possibility of compilers complaining about a narrowing cast too - especially as the entire Linux kernel assumes that pointers can be cast to unsigned long and back again with no loss.