Revision d6bd8194e2867e85ac2de63486d3b83ccfae4e62 authored by Michael Ellerman on 26 June 2017, 01:30:57 UTC, committed by Michael Ellerman on 26 June 2017, 13:25:08 UTC
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 3448890c32c3 ("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: 3448890c32c3 ("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>
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