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powerpc/32: Avoid miscompilation w/GCC 4.6.3 - don't inline copy_to/from_user()

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Larry Finger reported that his Powerbook G4 was no longer booting with v4.12-rc,
userspace was up but giving weird errors such as:

  udevd[64]: starting version 175
  udevd[64]: Unable to receive ctrl message: Bad address.
  modprobe: chdir(4.12-rc1): No such file or directory

He bisected the problem to commit 3448890c32 ("powerpc: get rid of zeroing,
switch to RAW_COPY_USER").

Al identified that the problem is actually a miscompilation by GCC 4.6.3, which
is exposed by the above commit.

Al also pointed out that inlining copy_to/from_user() is probably of little or
no benefit, which is correct. Using Anton's copy_to_user benchmark, with a
pathological single byte copy, we see a small increase in performance
by *removing* inlining:

  Before (inlined):
  # time ./copy_to_user -w -l 1 -i 10000000	( x 3 )
  real	0m22.063s
  real	0m22.059s
  real	0m22.076s

  After:
  # time ./copy_to_user -w -l 1 -i 10000000	( x 3 )
  real	0m21.325s
  real	0m21.299s
  real	0m21.364s

So as a small performance improvement and to avoid the miscompilation, drop
inlining copy_to/from_user() on 32-bit.

Fixes: 3448890c32 ("powerpc: get rid of zeroing, switch to RAW_COPY_USER")
Reported-by: Larry Finger <Larry.Finger@lwfinger.net>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Michael Ellerman 2017-06-26 11:30:57 +10:00
parent 797625deae
commit d6bd8194e2
1 changed files with 1 additions and 7 deletions
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8
arch/powerpc/include/asm/uaccess.h
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@ -267,13 +267,7 @@ do { \
extern unsigned long __copy_tofrom_user(void __user *to,
const void __user *from, unsigned long size);
#ifndef __powerpc64__
#define INLINE_COPY_FROM_USER
#define INLINE_COPY_TO_USER
#else /* __powerpc64__ */
#ifdef __powerpc64__
static inline unsigned long
raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
{