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Subject[RFC PATCH] arm64/mm: hit DEBUG_LOCKS_WARN_ON
Date
I'm running an arm64 kernel in a qemu guest and I hit this
DEBUG_LOCKS_WARN_ON and this patch removes the warning. The
interrupts_enabled(reqs) should reflect the irq->enabled state of the
kgdb test process when it hit the breakpoint, and that should be the
same as the current->hardirqs_enabled flag

[ 25.682116] kgdbts:RUN singlestep test 1000 iterations
[ 25.695926] ------------[ cut here ]------------
[ 25.696410] DEBUG_LOCKS_WARN_ON(current->hardirqs_enabled)
[ 25.697407] WARNING: CPU: 0 PID: 1 at ../kernel/locking/lockdep.c:3761 check_flags+0x64/0x198
[ 25.698349] Modules linked in:
[ 25.699144] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G T 4.19.0-next-20181030+ #6
[ 25.699739] Hardware name: linux,dummy-virt (DT)
[ 25.700359] pstate: 404003c5 (nZcv DAIF +PAN -UAO)
[ 25.700901] pc : check_flags+0x64/0x198
[ 25.701381] lr : check_flags+0x64/0x198
[ 25.701779] sp : ffffff800814b800
[ 25.702160] x29: ffffff800814b800 x28: ffffffc03ffbc000
[ 25.702721] x27: ffffff80081ee4d0 x26: 0000000000000000
[ 25.703240] x25: 0000000000000000 x24: 0000000000000002
[ 25.703753] x23: 0000000000000000 x22: 0000000000000000
[ 25.704276] x21: ffffff800aa23000 x20: 00000000000003c0
[ 25.704792] x19: ffffff8009c14000 x18: 00000000ffffffff
[ 25.705315] x17: 0000000000000000 x16: 0000000000000000
[ 25.705833] x15: 1740000000000000 x14: 2f6f69747269762f
[ 25.706356] x13: ffffffffffff0000 x12: ffffffffffffffff
[ 25.706877] x11: 000000000000000e x10: 7f7f7f7f7f7f7f7f
[ 25.707431] x9 : ffffff800814b800 x8 : 7261683e2d746e65
[ 25.707954] x7 : 72727563284e4f5f x6 : ffffff800aa2283e
[ 25.708471] x5 : 0000000000000000 x4 : 0000000000000000
[ 25.708990] x3 : ffffff8008318584 x2 : ffffffc03ffbc000
[ 25.709512] x1 : 0344ea595a8c0b00 x0 : 0000000000000000
[ 25.710104] Call trace:
[ 25.710553] check_flags+0x64/0x198
[ 25.711023] lock_acquire+0x60/0x248
[ 25.711477] call_step_hook+0x5c/0x190
[ 25.711937] single_step_handler+0x48/0xa0
[ 25.712399] do_debug_exception+0x104/0x160
[ 25.712846] el1_dbg+0x18/0xa8
[ 25.713252] el1_irq+0xa8/0x1c0
[ 25.713709] kgdbts_break_test+0x0/0x40
[ 25.714171] kgdbts_run_tests+0x2b0/0x430
[ 25.714637] configure_kgdbts+0x7c/0xb0
[ 25.715110] init_kgdbts+0x70/0xac
[ 25.715551] do_one_initcall+0x1fc/0x490
[ 25.716010] do_initcall_level+0x458/0x49c
[ 25.716462] do_initcalls+0x60/0xa4
[ 25.716892] do_basic_setup+0x3c/0x68
[ 25.717343] kernel_init_freeable+0x170/0x2b8
[ 25.717860] kernel_init+0x20/0x130
[ 25.718302] ret_from_fork+0x10/0x18
[ 25.718712] irq event stamp: 266621
[ 25.719209] hardirqs last enabled at (266621): [<ffffff80081e935c>] do_debug_exception+0x13c/0x160
[ 25.719949] hardirqs last disabled at (266620): [<ffffff8008215a58>] kgdb_roundup_cpus+0x30/0x38
[ 25.720675] softirqs last enabled at (266616): [<ffffff80081e9f24>] __do_softirq+0x4e4/0x52c
[ 25.721374] softirqs last disabled at (266609): [<ffffff8008279694>] irq_exit+0xbc/0x128
[ 25.722050] ---[ end trace ecb2b85abf3c30a2 ]---
[ 25.722537] possible reason: unannotated irqs-off.
[ 25.722960] irq event stamp: 266621

Rework code to drop the 'if (interrupts_enabled(regs))' before
trace_hardirqs_*() in function do_debug_exception().

We don't know why current->hardirqs_enabled and interrupts_enabled(regs)
don't match.

Fixes: 6afedcd23cfd ("arm64: mm: Add trace_irqflags annotations to do_debug_exception()")
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
---
arch/arm64/mm/fault.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 7d9571f4ae3d..9afe5a7ba55b 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -819,11 +819,9 @@ asmlinkage int __exception do_debug_exception(unsigned long addr,
int rv;

/*
- * Tell lockdep we disabled irqs in entry.S. Do nothing if they were
- * already disabled to preserve the last enabled/disabled addresses.
+ * Tell lockdep we disabled irqs in entry.S.
*/
- if (interrupts_enabled(regs))
- trace_hardirqs_off();
+ trace_hardirqs_off();

if (user_mode(regs) && instruction_pointer(regs) > TASK_SIZE)
arm64_apply_bp_hardening();
@@ -836,8 +834,7 @@ asmlinkage int __exception do_debug_exception(unsigned long addr,
rv = 0;
}

- if (interrupts_enabled(regs))
- trace_hardirqs_on();
+ trace_hardirqs_on();

return rv;
}
--
2.19.1
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