[PATCH 4.19 80/86] parisc: Add atomic64_set_release() define to avoid CPU soft lockups

Greg Kroah-Hartman
2020-07-27T14:12:24Z

From: John David Anglin <dave.anglin@bell.net>

commit be6577af0cef934ccb036445314072e8cb9217b9 upstream.

Stalls are quite frequent with recent kernels. I enabled
CONFIG_SOFTLOCKUP_DETECTOR and I caught the following stall:

watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [cc1:22803]
CPU: 0 PID: 22803 Comm: cc1 Not tainted 5.6.17+ #3
Hardware name: 9000/800/rp3440
IAOQ[0]: d_alloc_parallel+0x384/0x688
IAOQ[1]: d_alloc_parallel+0x388/0x688
RP(r2): d_alloc_parallel+0x134/0x688
Backtrace:
[<000000004036974c>] __lookup_slow+0xa4/0x200
[<0000000040369fc8>] walk_component+0x288/0x458
[<000000004036a9a0>] path_lookupat+0x88/0x198
[<000000004036e748>] filename_lookup+0xa0/0x168
[<000000004036e95c>] user_path_at_empty+0x64/0x80
[<000000004035d93c>] vfs_statx+0x104/0x158
[<000000004035dfcc>] __do_sys_lstat64+0x44/0x80
[<000000004035e5a0>] sys_lstat64+0x20/0x38
[<0000000040180054>] syscall_exit+0x0/0x14

The code was stuck in this loop in d_alloc_parallel:

4037d414: 0e 00 10 dc ldd 0(r16),ret0
4037d418: c7 fc 5f ed bb,< ret0,1f,4037d414 <d_alloc_parallel+0x384>
4037d41c: 08 00 02 40 nop

This is the inner loop of bit_spin_lock which is called by hlist_bl_unlock in
d_alloc_parallel:

static inline void bit_spin_lock(int bitnum, unsigned long *addr)
{
/*
* Assuming the lock is uncontended, this never enters
* the body of the outer loop. If it is contended, then
* within the inner loop a non-atomic test is used to
* busywait with less bus contention for a good time to
* attempt to acquire the lock bit.
*/
preempt_disable();
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
while (unlikely(test_and_set_bit_lock(bitnum, addr))) {
preempt_enable();
do {
cpu_relax();
} while (test_bit(bitnum, addr));
preempt_disable();
}
#endif
__acquire(bitlock);
}

After consideration, I realized that we must be losing bit unlocks.
Then, I noticed that we missed defining atomic64_set_release().
Adding this define fixes the stalls in bit operations.

Signed-off-by: Dave Anglin <dave.anglin@bell.net>
Cc: stable@vger.kernel.org
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/parisc/include/asm/atomic.h | 2 ++
1 file changed, 2 insertions(+)

--- a/arch/parisc/include/asm/atomic.h
+++ b/arch/parisc/include/asm/atomic.h
@@ -212,6 +212,8 @@ atomic64_set(atomic64_t *v, s64 i)
_atomic_spin_unlock_irqrestore(v, flags);
}

+#define atomic64_set_release(v, i) atomic64_set((v), (i))
+
static __inline__ s64
atomic64_read(const atomic64_t *v)
{