Revert changes to convert to ->poll_mask() and aio IOCB_CMD_POLL

The poll() changes were not well thought out, and completely
unexplained.  They also caused a huge performance regression, because
"->poll()" was no longer a trivial file operation that just called down
to the underlying file operations, but instead did at least two indirect
calls.

Indirect calls are sadly slow now with the Spectre mitigation, but the
performance problem could at least be largely mitigated by changing the
"->get_poll_head()" operation to just have a per-file-descriptor pointer
to the poll head instead.  That gets rid of one of the new indirections.

But that doesn't fix the new complexity that is completely unwarranted
for the regular case.  The (undocumented) reason for the poll() changes
was some alleged AIO poll race fixing, but we don't make the common case
slower and more complex for some uncommon special case, so this all
really needs way more explanations and most likely a fundamental
redesign.

[ This revert is a revert of about 30 different commits, not reverted
  individually because that would just be unnecessarily messy  - Linus ]

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 11 deletions

diff --git a/fs/timerfd.c b/fs/timerfd.c
index d84a2bee4f82..cdad49da3ff7 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -226,20 +226,21 @@ static int timerfd_release(struct inode *inode, struct file *file)
 	kfree_rcu(ctx, rcu);
 	return 0;
 }
-	
-static struct wait_queue_head *timerfd_get_poll_head(struct file *file,
-		__poll_t eventmask)
+
+static __poll_t timerfd_poll(struct file *file, poll_table *wait)
 {
 	struct timerfd_ctx *ctx = file->private_data;
+	__poll_t events = 0;
+	unsigned long flags;
 
-	return &ctx->wqh;
-}
+	poll_wait(file, &ctx->wqh, wait);
 
-static __poll_t timerfd_poll_mask(struct file *file, __poll_t eventmask)
-{
-	struct timerfd_ctx *ctx = file->private_data;
+	spin_lock_irqsave(&ctx->wqh.lock, flags);
+	if (ctx->ticks)
+		events |= EPOLLIN;
+	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
 
-	return ctx->ticks ? EPOLLIN : 0;
+	return events;
 }
 
 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
@@ -363,8 +364,7 @@ static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg
 
 static const struct file_operations timerfd_fops = {
 	.release	= timerfd_release,
-	.get_poll_head	= timerfd_get_poll_head,
-	.poll_mask	= timerfd_poll_mask,
+	.poll		= timerfd_poll,
 	.read		= timerfd_read,
 	.llseek		= noop_llseek,
 	.show_fdinfo	= timerfd_show,