[PATCH 6.1 190/259] powerpc/watchpoints: Disable preemption in thread_change_pc()

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6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Benjamin Gray <bgray@xxxxxxxxxxxxx>

[ Upstream commit cc879ab3ce39bc39f9b1d238b283f43a5f6f957d ]

thread_change_pc() uses CPU local data, so must be protected from
swapping CPUs while it is reading the breakpoint struct.

The error is more noticeable after 1e60f3564bad ("powerpc/watchpoints:
Track perf single step directly on the breakpoint"), which added an
unconditional __this_cpu_read() call in thread_change_pc(). However the
existing __this_cpu_read() that runs if a breakpoint does need to be
re-inserted has the same issue.

Signed-off-by: Benjamin Gray <bgray@xxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://msgid.link/20230829063457.54157-2-bgray@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/powerpc/kernel/hw_breakpoint.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index 8db1a15d7acbe..a72f86c130488 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -505,11 +505,13 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
 	struct arch_hw_breakpoint *info;
 	int i;
 
+	preempt_disable();
+
 	for (i = 0; i < nr_wp_slots(); i++) {
 		if (unlikely(tsk->thread.last_hit_ubp[i]))
 			goto reset;
 	}
-	return;
+	goto out;
 
 reset:
 	regs_set_return_msr(regs, regs->msr & ~MSR_SE);
@@ -518,6 +520,9 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
 		__set_breakpoint(i, info);
 		tsk->thread.last_hit_ubp[i] = NULL;
 	}
+
+out:
+	preempt_enable();
 }
 
 static bool is_larx_stcx_instr(int type)
-- 
2.40.1






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