locking/lockdep: Remove more raw_cpu_read() usage

I initially thought raw_cpu_read() was OK, since if it is !0 we have
IRQs disabled and can't get migrated, so if we get migrated both CPUs
must have 0 and it doesn't matter which 0 we read.

And while that is true; it isn't the whole store, on pretty much all
architectures (except x86) this can result in computing the address for
one CPU, getting migrated, the old CPU continuing execution with another
task (possibly setting recursion) and then the new CPU reading the value
of the old CPU, which is no longer 0.

Similer to:

  baffd723e44d ("lockdep: Revert "lockdep: Use raw_cpu_*() for per-cpu variables"")

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201026152256.GB2651@hirez.programming.kicks-ass.net

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index fc206aefa970829f720aea5e6f9987171f48b1ae..11028497d4df75bae051d5bed33a03c6e284c324 100644 (file)
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -84,7 +84,7 @@ static inline bool lockdep_enabled(void)
        if (!debug_locks)
                return false;
 
-       if (raw_cpu_read(lockdep_recursion))
+       if (this_cpu_read(lockdep_recursion))
                return false;
 
        if (current->lockdep_recursion)