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#ifndef _ASM_POWERPC_CURRENT_H
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#define _ASM_POWERPC_CURRENT_H
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#ifdef __KERNEL__
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/*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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struct task_struct;
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#ifdef __powerpc64__
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#include <linux/stddef.h>
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#include <asm/paca.h>
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[POWERPC] Make current preempt-safe
Repeated -j20 kernel builds on a G5 Quad running an SMP PREEMPT kernel
would often collapse within a day, some exec failing with "Bad address".
In each case examined, load_elf_binary was doing a kernel_read, but
generic_file_aio_read's access_ok saw current->thread.fs.seg as USER_DS
instead of KERNEL_DS.
objdump of filemap.o shows gcc 4.1.0 emitting "mr r5,r13 ... ld r9,416(r5)"
here for get_paca()->__current, instead of the expected and much more usual
"ld r9,416(r13)"; I've seen other gcc4s do the same, but perhaps not gcc3s.
So, if the task is preempted and rescheduled on a different cpu in between
the mr and the ld, r5 will be looking at a different paca_struct from the
one it's now on, pick up the wrong __current, and perhaps the wrong seg.
Presumably much worse could happen elsewhere, though that split is rare.
Other architectures appear to be safe (x86_64's read_pda is more limiting
than get_paca), but ppc64 needs to force "current" into one instruction.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
18 years ago
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static inline struct task_struct *get_current(void)
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{
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struct task_struct *task;
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__asm__ __volatile__("ld %0,%1(13)"
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: "=r" (task)
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: "i" (offsetof(struct paca_struct, __current)));
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return task;
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}
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#define current get_current()
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#else
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/*
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* We keep `current' in r2 for speed.
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*/
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register struct task_struct *current asm ("r2");
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#endif
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#endif /* __KERNEL__ */
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#endif /* _ASM_POWERPC_CURRENT_H */
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