nfsd: Don't call freezable_schedule_timeout() after each successful page...

nfsd: Don't call freezable_schedule_timeout() after each successful page allocation in svc_alloc_arg().

When commit 39039024 ("nfsd: don't allow nfsd threads to be
signalled.") is backported to 5.10, it was adjusted considering commit
3feac2b5 ("sunrpc: exclude from freezer when waiting for requests:").

However, 3feac2b5 is based on commit f6e70aab ("SUNRPC: refresh
rq_pages using a bulk page allocator"), which converted page-by-page
allocation to a batch allocation, so schedule_timeout() is placed
un-nested.

As a result, the backported commit 7229200f ("nfsd: don't allow nfsd
threads to be signalled.") placed freezable_schedule_timeout() in the wrong
place.

Now, freezable_schedule_timeout() is called after every successful page
allocation, and we see 30%+ performance regression on 5.10.220 in our
test suite.

Let's move it to the correct place so that freezable_schedule_timeout()
is called only when page allocation fails.

Fixes: 7229200f ("nfsd: don't allow nfsd threads to be signalled.")
Reported-by: Hughdan Liu <hughliu@amazon.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>