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, 13 insertions, 16 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index a8fb0020ba5c..cd888d4ee605 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -402,7 +402,8 @@ static struct poolinfo {
 /*
  * Static global variables
  */
-static DECLARE_WAIT_QUEUE_HEAD(random_wait);
+static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
+static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
 static struct fasync_struct *fasync;
 
 static DEFINE_SPINLOCK(random_ready_list_lock);
@@ -721,8 +722,8 @@ retry:
 
                 /* should we wake readers? */
                 if (entropy_bits >= random_read_wakeup_bits &&
-                    wq_has_sleeper(&random_wait)) {
-                        wake_up_interruptible_poll(&random_wait, POLLIN);
+                    wq_has_sleeper(&random_read_wait)) {
+                        wake_up_interruptible(&random_read_wait);
                         kill_fasync(&fasync, SIGIO, POLL_IN);
                 }
                 /* If the input pool is getting full, send some
@@ -1396,7 +1397,7 @@ retry:
         trace_debit_entropy(r->name, 8 * ibytes);
         if (ibytes &&
             (r->entropy_count >> ENTROPY_SHIFT) < random_write_wakeup_bits) {
-                wake_up_interruptible_poll(&random_wait, POLLOUT);
+                wake_up_interruptible(&random_write_wait);
                 kill_fasync(&fasync, SIGIO, POLL_OUT);
         }
 
@@ -1838,7 +1839,7 @@ _random_read(int nonblock, char __user *buf, size_t nbytes)
                 if (nonblock)
                         return -EAGAIN;
 
-                wait_event_interruptible(random_wait,
+                wait_event_interruptible(random_read_wait,
                         ENTROPY_BITS(&input_pool) >=
                         random_read_wakeup_bits);
                 if (signal_pending(current))
@@ -1875,17 +1876,14 @@ urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
         return ret;
 }
 
-static struct wait_queue_head *
-random_get_poll_head(struct file *file, __poll_t events)
-{
-        return &random_wait;
-}
-
 static __poll_t
-random_poll_mask(struct file *file, __poll_t events)
+random_poll(struct file *file, poll_table * wait)
 {
-        __poll_t mask = 0;
+        __poll_t mask;
 
+        poll_wait(file, &random_read_wait, wait);
+        poll_wait(file, &random_write_wait, wait);
+        mask = 0;
         if (ENTROPY_BITS(&input_pool) >= random_read_wakeup_bits)
                 mask |= EPOLLIN | EPOLLRDNORM;
         if (ENTROPY_BITS(&input_pool) < random_write_wakeup_bits)
@@ -1992,8 +1990,7 @@ static int random_fasync(int fd, struct file *filp, int on)
 const struct file_operations random_fops = {
         .read  = random_read,
         .write = random_write,
-        .get_poll_head  = random_get_poll_head,
-        .poll_mask  = random_poll_mask,
+        .poll  = random_poll,
         .unlocked_ioctl = random_ioctl,
         .fasync = random_fasync,
         .llseek = noop_llseek,
@@ -2326,7 +2323,7 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
          * We'll be woken up again once below random_write_wakeup_thresh,
          * or when the calling thread is about to terminate.
          */
-        wait_event_interruptible(random_wait, kthread_should_stop() ||
+        wait_event_interruptible(random_write_wait, kthread_should_stop() ||
                         ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits);
         mix_pool_bytes(poolp, buffer, count);
         credit_entropy_bits(poolp, entropy);