From: Dmitry Vyukov <dvyukov@google.com>
To: Peter Zijlstra <peterz@infradead.org>,
linux-sparse@vger.kernel.org, Christopher Li <sparse@chrisli.org>
Cc: kbuild test robot <fengguang.wu@intel.com>,
kbuild-all@01.org, LKML <linux-kernel@vger.kernel.org>,
tipbuild@zytor.com, Ingo Molnar <mingo@kernel.org>
Subject: Re: [tip:locking/core 9/11] include/asm-generic/atomic-instrumented.h:288:24: sparse: cast truncates bits from constant value (100 becomes 0)
Date: Tue, 13 Mar 2018 14:08:13 +0300 [thread overview]
Message-ID: <CACT4Y+b+ECV+6hky_cq1tg2BbYbsv1c_xGYrgzjiLfSbx21rVA@mail.gmail.com> (raw)
In-Reply-To: <20180313104652.GK4043@hirez.programming.kicks-ass.net>
On Tue, Mar 13, 2018 at 1:46 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, Mar 13, 2018 at 11:49:17AM +0300, Dmitry Vyukov wrote:
>> On Mon, Mar 12, 2018 at 6:17 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
>> > On Mon, Mar 12, 2018 at 5:52 PM, kbuild test robot
>> >> kernel/locking/qspinlock.c:418:22: sparse: incorrect type in assignment (different modifiers) @@ expected struct mcs_spinlock *prev @@ got struct struct mcs_spinlock *prev @@
>> >> kernel/locking/qspinlock.c:418:22: expected struct mcs_spinlock *prev
>> >> kernel/locking/qspinlock.c:418:22: got struct mcs_spinlock [pure] *
>
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 283 static __always_inline unsigned long
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 284 cmpxchg_size(volatile void *ptr, unsigned long old, unsigned long new, int size)
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 285 {
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 286 switch (size) {
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 287 case 1:
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 @288 return arch_cmpxchg((u8 *)ptr, (u8)old, (u8)new);
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 289 case 2:
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 290 return arch_cmpxchg((u16 *)ptr, (u16)old, (u16)new);
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 291 case 4:
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 292 return arch_cmpxchg((u32 *)ptr, (u32)old, (u32)new);
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 293 case 8:
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 294 BUILD_BUG_ON(sizeof(unsigned long) != 8);
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 295 return arch_cmpxchg((u64 *)ptr, (u64)old, (u64)new);
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 296 }
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 297 BUILD_BUG();
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 298 return 0;
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 299 }
>> >> b06ed71a6 Dmitry Vyukov 2018-01-29 300
>
>> It seems that this is due to this guy:
>>
>> static __always_inline int trylock_clear_pending(struct qspinlock *lock)
>> {
>> struct __qspinlock *l = (void *)lock;
>>
>> return !READ_ONCE(l->locked) &&
>> (cmpxchg_acquire(&l->locked_pending, _Q_PENDING_VAL,
>> _Q_LOCKED_VAL) == _Q_PENDING_VAL);
>> }
>>
>> _Q_PENDING_VAL is 0x100. However, locked_pending is 2 bytes. So it
>> seems that compiler checks all switch cases, this inevitably will lead
>> to such warnings.
>>
>> Any suggestion on how to resolve this? Leave as is?
>
> I'm not sure I understand what it thinks is wrong. Can't we fix sparse
> to not be stupid? The actual compilers don't seem to a have a problem
> with this.
That would be best of course. +sparse mailing list and Christopher.
>> Off the top of my head I can think of the following solution:
>>
>> switch (size) {
>> case 1:
>> return arch_cmpxchg((u8 *)ptr, (u8)(old * (size !=
>> 1)), (u8)(new * (size != 1)));
>> case 2:
>> return arch_cmpxchg((u16 *)ptr, (u16)(old * (size !=
>> 2)), (u16)(new * (size != 2)));
>>
>> But it's too ugly.
>
> Yes agreed, that's horrendous.
next prev parent reply other threads:[~2018-03-13 11:08 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-12 14:52 [tip:locking/core 9/11] include/asm-generic/atomic-instrumented.h:288:24: sparse: cast truncates bits from constant value (100 becomes 0) kbuild test robot
2018-03-12 15:17 ` Dmitry Vyukov
2018-03-13 8:49 ` Dmitry Vyukov
2018-03-13 10:46 ` Peter Zijlstra
2018-03-13 11:08 ` Dmitry Vyukov [this message]
2018-03-13 17:29 ` Christopher Li
2018-03-13 18:00 ` Luc Van Oostenryck
2018-03-13 18:08 ` Peter Zijlstra
2018-03-13 20:01 ` Luc Van Oostenryck
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CACT4Y+b+ECV+6hky_cq1tg2BbYbsv1c_xGYrgzjiLfSbx21rVA@mail.gmail.com \
--to=dvyukov@google.com \
--cc=fengguang.wu@intel.com \
--cc=kbuild-all@01.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-sparse@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=sparse@chrisli.org \
--cc=tipbuild@zytor.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).