eventfd: move 'eventfd-count' printing out of spinlock

When printing eventfd->count, interrupts will be disabled and a spinlock
will be obtained, competing with eventfd_write(). By moving the
"eventfd-count" print out of the spinlock and merging multiple
seq_printf() into one, it could improve a bit, just like timerfd_show().

Signed-off-by: Wen Yang <wenyang.linux@foxmail.com>
Link: https://lore.kernel.org/r/tencent_B0B3D2BD9861FD009E03AB18A81783322709@qq.com
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dylan Yudaken <dylany@fb.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Eric Biggers <ebiggers@google.com>
Cc: <linux-fsdevel@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/eventfd.c b/fs/eventfd.c
index 0252b71099fbca0f8fa50252a4239be1e637221c..fc4d8109076392385d3b92907c692d6b3a57aada 100644 (file)
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -283,13 +283,18 @@ static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t c
 static void eventfd_show_fdinfo(struct seq_file *m, struct file *f)
 {
        struct eventfd_ctx *ctx = f->private_data;
+       __u64 cnt;
 
        spin_lock_irq(&ctx->wqh.lock);
-       seq_printf(m, "eventfd-count: %16llx\n",
-                  (unsigned long long)ctx->count);
+       cnt = ctx->count;
        spin_unlock_irq(&ctx->wqh.lock);
-       seq_printf(m, "eventfd-id: %d\n", ctx->id);
-       seq_printf(m, "eventfd-semaphore: %d\n",
+
+       seq_printf(m,
+                  "eventfd-count: %16llx\n"
+                  "eventfd-id: %d\n"
+                  "eventfd-semaphore: %d\n",
+                  cnt,
+                  ctx->id,
                   !!(ctx->flags & EFD_SEMAPHORE));
 }
 #endif