s390/diag: avoid lockdep recursion

The diagnose tracer will indirectly call back into the lockdep code
when lockdep does not expect it (arch_spinlock). This causes lockdep
to disable itself and therefore we don't have a working lock
dependency validator anymore.

This patch effectively disables tracing of diag 0x9c and 0x44 if
lockdep is enabled.  If however lockdep is enabled spinlocks are
mainly implemented using a trylock variant, which will not issue any
diag 0x9c or 0x44. So this change has hardly any effect on tracing
except when arch_spinlock and friends are explicitly used.

Reported-and-Tested-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/kernel/trace.c b/arch/s390/kernel/trace.c
index 21a5df99552bce6e4f84c872acdda43e6c5732c3..dde7654f5c68e5d117d3493d9c0f130f2e24e830 100644 (file)
--- a/arch/s390/kernel/trace.c
+++ b/arch/s390/kernel/trace.c
@@ -18,6 +18,9 @@ void trace_s390_diagnose_norecursion(int diag_nr)
        unsigned long flags;
        unsigned int *depth;
 
+       /* Avoid lockdep recursion. */
+       if (IS_ENABLED(CONFIG_LOCKDEP))
+               return;
        local_irq_save(flags);
        depth = this_cpu_ptr(&diagnose_trace_depth);
        if (*depth == 0) {