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Subject[PATCHv7 10/11] powerpc: snapshot thread flags
Date
Some thread flags can be set remotely, and so even when IRQs are
disabled, the flags can change under our feet. Generally this is
unlikely to cause a problem in practice, but it is somewhat unsound, and
KCSAN will legitimately warn that there is a data race.

To avoid such issues, a snapshot of the flags has to be taken prior to
using them. Some places already use READ_ONCE() for that, others do not.

Convert them all to the new flag accessor helpers.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
---
arch/powerpc/kernel/interrupt.c | 13 ++++++-------
arch/powerpc/kernel/ptrace/ptrace.c | 3 +--
2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index 1c821b76c2d1..ff25888ffc25 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -181,7 +181,7 @@ notrace long system_call_exception(long r3, long r4, long r5,

local_irq_enable();

- if (unlikely(current_thread_info()->flags & _TIF_SYSCALL_DOTRACE)) {
+ if (unlikely(read_thread_flags() & _TIF_SYSCALL_DOTRACE)) {
if (unlikely(trap_is_unsupported_scv(regs))) {
/* Unsupported scv vector */
_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
@@ -343,7 +343,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)
unsigned long ti_flags;

again:
- ti_flags = READ_ONCE(current_thread_info()->flags);
+ ti_flags = read_thread_flags();
while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) {
local_irq_enable();
if (ti_flags & _TIF_NEED_RESCHED) {
@@ -359,7 +359,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)
do_notify_resume(regs, ti_flags);
}
local_irq_disable();
- ti_flags = READ_ONCE(current_thread_info()->flags);
+ ti_flags = read_thread_flags();
}

if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && IS_ENABLED(CONFIG_PPC_FPU)) {
@@ -437,7 +437,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
/* Check whether the syscall is issued inside a restartable sequence */
rseq_syscall(regs);

- ti_flags = current_thread_info()->flags;
+ ti_flags = read_thread_flags();

if (unlikely(r3 >= (unsigned long)-MAX_ERRNO) && is_not_scv) {
if (likely(!(ti_flags & (_TIF_NOERROR | _TIF_RESTOREALL)))) {
@@ -532,8 +532,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
unsigned long flags;
unsigned long ret = 0;
unsigned long kuap;
- bool stack_store = current_thread_info()->flags &
- _TIF_EMULATE_STACK_STORE;
+ bool stack_store = read_thread_flags() & _TIF_EMULATE_STACK_STORE;

if (regs_is_unrecoverable(regs))
unrecoverable_exception(regs);
@@ -554,7 +553,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
again:
if (IS_ENABLED(CONFIG_PREEMPT)) {
/* Return to preemptible kernel context */
- if (unlikely(current_thread_info()->flags & _TIF_NEED_RESCHED)) {
+ if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
if (preempt_count() == 0)
preempt_schedule_irq();
}
diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
index 7c7093c17c45..c43f77e2ac31 100644
--- a/arch/powerpc/kernel/ptrace/ptrace.c
+++ b/arch/powerpc/kernel/ptrace/ptrace.c
@@ -260,8 +260,7 @@ long do_syscall_trace_enter(struct pt_regs *regs)
{
u32 flags;

- flags = READ_ONCE(current_thread_info()->flags) &
- (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
+ flags = read_thread_flags() & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);

if (flags) {
int rc = tracehook_report_syscall_entry(regs);
--
2.11.0
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