From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>,
Randy Dunlap <rdunlap@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
broonie@kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-next@vger.kernel.org, mhocko@suse.cz,
mm-commits@vger.kernel.org, sfr@canb.auug.org.au,
Linus Torvalds <torvalds@linux-foundation.org>,
viro@zeniv.linux.org.uk, x86@kernel.org,
Steven Rostedt <rostedt@goodmis.org>
Subject: [PATCH] x86/uaccess: Remove redundant likely/unlikely annotations
Date: Fri, 29 May 2020 12:25:05 -0500 [thread overview]
Message-ID: <20200529172505.fdjppgquujab7ayv@treble> (raw)
In-Reply-To: <20200529165419.GF706460@hirez.programming.kicks-ass.net>
On Fri, May 29, 2020 at 06:54:19PM +0200, Peter Zijlstra wrote:
> On Fri, May 29, 2020 at 11:50:11AM -0500, Josh Poimboeuf wrote:
> > The nested likelys seem like overkill anyway -- user_access_begin() is
> > __always_inline and it already has unlikely(), which should be
> > propagated.
> >
> > So just remove the outer likelys?
>
> That fixes it. Ack!
If there are no objections to the patch, I can add it to my objtool-core
branch unless anybody else wants to take it. It only affects
linux-next.
---8<---
From: Josh Poimboeuf <jpoimboe@redhat.com>
Subject: [PATCH] x86/uaccess: Remove redundant likely/unlikely annotations
Since user_access_begin() already has an unlikely() annotation for its
access_ok() check, "if (likely(user_access_begin))" results in nested
likely annotations. When combined with CONFIG_TRACE_BRANCH_PROFILING,
GCC converges the error/success paths of the nested ifs, using a
register value to distinguish between them.
While the code is technically uaccess safe, it complicates the
branch-profiling generated code. It also confuses objtool, because it
doesn't do register value tracking, resulting in the following warnings:
arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0x2a4: call to memset() with UACCESS enabled
arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_to_user()+0x243: return with UACCESS enabled
The outer likely annotations aren't actually needed anyway, since the
compiler propagates the error path coldness when it inlines
user_access_begin().
Fixes: 18372ef87665 ("x86_64: csum_..._copy_..._user(): switch to unsafe_..._user()")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
arch/x86/lib/csum-wrappers_64.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/lib/csum-wrappers_64.c b/arch/x86/lib/csum-wrappers_64.c
index a12b8629206d..ee63d7576fd2 100644
--- a/arch/x86/lib/csum-wrappers_64.c
+++ b/arch/x86/lib/csum-wrappers_64.c
@@ -27,7 +27,7 @@ csum_and_copy_from_user(const void __user *src, void *dst,
might_sleep();
*errp = 0;
- if (!likely(user_access_begin(src, len)))
+ if (!user_access_begin(src, len))
goto out_err;
/*
@@ -89,7 +89,7 @@ csum_and_copy_to_user(const void *src, void __user *dst,
might_sleep();
- if (unlikely(!user_access_begin(dst, len))) {
+ if (!user_access_begin(dst, len)) {
*errp = -EFAULT;
return 0;
}
--
2.21.3
next prev parent reply other threads:[~2020-05-29 17:33 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200513175005.1f4839360c18c0238df292d1@linux-foundation.org>
2020-05-14 3:31 ` mmotm 2020-05-13-20-30 uploaded Andrew Morton
2020-05-14 15:32 ` mmotm 2020-05-13-20-30 uploaded (objtool warnings) Randy Dunlap
2020-05-28 15:54 ` Josh Poimboeuf
2020-05-28 17:04 ` Josh Poimboeuf
2020-05-28 17:20 ` Peter Zijlstra
2020-05-29 13:57 ` Christoph Hellwig
2020-05-29 14:35 ` Peter Zijlstra
2020-05-29 14:53 ` Peter Zijlstra
2020-05-29 15:33 ` Peter Zijlstra
2020-05-29 16:05 ` Josh Poimboeuf
2020-05-29 16:12 ` Peter Zijlstra
2020-05-29 16:50 ` Josh Poimboeuf
2020-05-29 16:54 ` Peter Zijlstra
2020-05-29 17:25 ` Josh Poimboeuf [this message]
2020-05-29 18:29 ` [PATCH] x86/uaccess: Remove redundant likely/unlikely annotations Randy Dunlap
2020-05-29 19:31 ` mmotm 2020-05-13-20-30 uploaded (objtool warnings) Linus Torvalds
2020-05-29 20:08 ` Al Viro
2020-05-29 20:14 ` Al Viro
2020-05-15 23:30 ` mmotm 2020-05-15-16-29 uploaded Andrew Morton
2020-05-16 5:53 ` Stephen Rothwell
2020-05-18 23:15 ` Stephen Rothwell
2020-05-20 4:48 ` mmotm 2020-05-19-21-47 uploaded Andrew Morton
2020-05-22 3:43 ` mmotm 2020-05-21-20-42 uploaded Andrew Morton
2020-05-23 3:36 ` mmotm 2020-05-22-20-35 uploaded Andrew Morton
2020-05-23 15:08 ` mmotm 2020-05-22-20-35 uploaded (phy/intel/phy-intel-combo.c) Randy Dunlap
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