f862eefec0
It turns out the kernel relies on barrier() to force a reload of the
percpu offset value. Since we can't easily modify the definition of
barrier() to include "tp" as an output register, we instead provide a
definition of __my_cpu_offset as extended assembly that includes a fake
stack read to hazard against barrier(), forcing gcc to know that it
must reread "tp" and recompute anything based on "tp" after a barrier.
This fixes observed hangs in the slub allocator when we are looping
on a percpu cmpxchg_double.
A similar fix for ARMv7 was made in June in change 509eb76ebf.
Cc: stable@vger.kernel.org
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
53 lines
1.8 KiB
C
53 lines
1.8 KiB
C
/*
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* Copyright 2010 Tilera Corporation. All Rights Reserved.
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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, version 2.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
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* NON INFRINGEMENT. See the GNU General Public License for
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* more details.
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*/
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#ifndef _ASM_TILE_PERCPU_H
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#define _ASM_TILE_PERCPU_H
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register unsigned long my_cpu_offset_reg asm("tp");
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#ifdef CONFIG_PREEMPT
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/*
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* For full preemption, we can't just use the register variable
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* directly, since we need barrier() to hazard against it, causing the
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* compiler to reload anything computed from a previous "tp" value.
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* But we also don't want to use volatile asm, since we'd like the
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* compiler to be able to cache the value across multiple percpu reads.
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* So we use a fake stack read as a hazard against barrier().
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* The 'U' constraint is like 'm' but disallows postincrement.
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*/
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static inline unsigned long __my_cpu_offset(void)
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{
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unsigned long tp;
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register unsigned long *sp asm("sp");
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asm("move %0, tp" : "=r" (tp) : "U" (*sp));
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return tp;
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}
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#define __my_cpu_offset __my_cpu_offset()
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#else
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/*
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* We don't need to hazard against barrier() since "tp" doesn't ever
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* change with PREEMPT_NONE, and with PREEMPT_VOLUNTARY it only
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* changes at function call points, at which we are already re-reading
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* the value of "tp" due to "my_cpu_offset_reg" being a global variable.
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*/
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#define __my_cpu_offset my_cpu_offset_reg
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#endif
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#define set_my_cpu_offset(tp) (my_cpu_offset_reg = (tp))
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#include <asm-generic/percpu.h>
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#endif /* _ASM_TILE_PERCPU_H */
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