| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.10 22/71] MIPS: Remove BUG_ON(!is_fpu_owner()) in do_ade() | Date | Mon, 15 Sep 2014 12:26:20 -0700 |
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3.10-stable review patch. If anyone has any objections, please let me know.
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From: Huacai Chen <chenhc@lemote.com>
commit 2e5767a27337812f6850b3fa362419e2f085e5c3 upstream.
In do_ade(), is_fpu_owner() isn't preempt-safe. For example, when an unaligned ldc1 is executed, do_cpu() is called and then FPU will be enabled (and TIF_USEDFPU will be set for the current process). Then, do_ade() is called because the access is unaligned. If the current process is preempted at this time, TIF_USEDFPU will be cleard. So when the process is scheduled again, BUG_ON(!is_fpu_owner()) is triggered.
This small program can trigger this BUG in a preemptible kernel:
int main (int argc, char *argv[]) { double u64[2];
while (1) { asm volatile ( ".set push \n\t" ".set noreorder \n\t" "ldc1 $f3, 4(%0) \n\t" ".set pop \n\t" ::"r"(u64): ); }
return 0; }
V2: Remove the BUG_ON() unconditionally due to Paul's suggestion.
Signed-off-by: Huacai Chen <chenhc@lemote.com> Signed-off-by: Jie Chen <chenj@lemote.com> Signed-off-by: Rui Wang <wangr@lemote.com> Cc: John Crispin <john@phrozen.org> Cc: Steven J. Hill <Steven.Hill@imgtec.com> Cc: linux-mips@linux-mips.org Cc: Fuxin Zhang <zhangfx@lemote.com> Cc: Zhangjin Wu <wuzhangjin@gmail.com> Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- arch/mips/kernel/unaligned.c | 1 - 1 file changed, 1 deletion(-)
--- a/arch/mips/kernel/unaligned.c +++ b/arch/mips/kernel/unaligned.c @@ -604,7 +604,6 @@ static void emulate_load_store_insn(stru case sdc1_op: die_if_kernel("Unaligned FP access in kernel code", regs); BUG_ON(!used_math()); - BUG_ON(!is_fpu_owner()); lose_fpu(1); /* Save FPU state for the emulator. */ res = fpu_emulator_cop1Handler(regs, ¤t->thread.fpu, 1,
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