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riscv: fix race when vmap stack overflow
[ Upstream commit 7e18643 ] Currently, when detecting vmap stack overflow, riscv firstly switches to the so called shadow stack, then use this shadow stack to call the get_overflow_stack() to get the overflow stack. However, there's a race here if two or more harts use the same shadow stack at the same time. To solve this race, we introduce spin_shadow_stack atomic var, which will be swap between its own address and 0 in atomic way, when the var is set, it means the shadow_stack is being used; when the var is cleared, it means the shadow_stack isn't being used. Fixes: 31da94c ("riscv: add VMAP_STACK overflow detection") Signed-off-by: Jisheng Zhang <jszhang@kernel.org> Suggested-by: Guo Ren <guoren@kernel.org> Reviewed-by: Guo Ren <guoren@kernel.org> Link: https://lore.kernel.org/r/20221030124517.2370-1-jszhang@kernel.org [Palmer: Add AQ to the swap, and also some comments.] Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
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