aio: use atomic_try_cmpxchg in __get_reqs_available

Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in __get_reqs_available.  x86 CMPXCHG instruction returns success in ZF
flag, so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).

Also, atomic_try_cmpxchg implicitly assigns old *ptr value to "old" when
cmpxchg fails, enabling further code simplifications.

No functional change intended.

Link: https://lkml.kernel.org/r/20220714164851.3055-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/aio.c b/fs/aio.c
index 606613e9d1f4fd09899f2237fa26ee4b3848e01e..5b2ff20ad32298e827b8cb68da24160e8b91ae41 100644 (file)
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -951,16 +951,13 @@ static bool __get_reqs_available(struct kioctx *ctx)
        local_irq_save(flags);
        kcpu = this_cpu_ptr(ctx->cpu);
        if (!kcpu->reqs_available) {
-               int old, avail = atomic_read(&ctx->reqs_available);
+               int avail = atomic_read(&ctx->reqs_available);
 
                do {
                        if (avail < ctx->req_batch)
                                goto out;
-
-                       old = avail;
-                       avail = atomic_cmpxchg(&ctx->reqs_available,
-                                              avail, avail - ctx->req_batch);
-               } while (avail != old);
+               } while (!atomic_try_cmpxchg(&ctx->reqs_available,
+                                            &avail, avail - ctx->req_batch));
 
                kcpu->reqs_available += ctx->req_batch;
        }