Revert "fs/pipe: use kvcalloc to allocate a pipe_buffer array"

This reverts commit 5a519c8.

It turns out that making the pipe almost arbitrarily large has some
rather unexpected downsides.  The kernel test robot reports a kernel
warning that is due to pipe->max_usage now growing to the point where
the iter_file_splice_write() buffer allocation can no longer be
satisfied as a slab allocation, and the

        int nbufs = pipe->max_usage;
        struct bio_vec *array = kcalloc(nbufs, sizeof(struct bio_vec),
                                        GFP_KERNEL);

code sequence there will now always fail as a result.

That code could be modified to use kvcalloc() too, but I feel very
uncomfortable making those kinds of changes for a very niche use case
that really should have other options than make these kinds of
fundamental changes to pipe behavior.

Maybe the CRIU process dumping should be multi-threaded, and use
multiple pipes and multiple cores, rather than try to use one larger
pipe to minimize splice() calls.

Reported-by: kernel test robot <[email protected]>
Link: https://lore.kernel.org/all/20220420073717.GD16310@xsang-OptiPlex-9020/
Cc: Andrei Vagin <[email protected]>
Cc: Dmitry Safonov <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: torvalds

fs/pipe.c

@@ -804,7 +804,7 @@ struct pipe_inode_info *alloc_pipe_info(void)
 	if (too_many_pipe_buffers_hard(user_bufs) && pipe_is_unprivileged_user())
 		goto out_revert_acct;
 
-	pipe->bufs = kvcalloc(pipe_bufs, sizeof(struct pipe_buffer),
+	pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
 			     GFP_KERNEL_ACCOUNT);
 
 	if (pipe->bufs) {
@@ -849,7 +849,7 @@ void free_pipe_info(struct pipe_inode_info *pipe)
 #endif
 	if (pipe->tmp_page)
 		__free_page(pipe->tmp_page);
-	kvfree(pipe->bufs);
+	kfree(pipe->bufs);
 	kfree(pipe);
 }
 
@@ -1264,7 +1264,8 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
 	if (nr_slots < n)
 		return -EBUSY;
 
-	bufs = kvcalloc(nr_slots, sizeof(*bufs), GFP_KERNEL_ACCOUNT);
+	bufs = kcalloc(nr_slots, sizeof(*bufs),
+		       GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
 	if (unlikely(!bufs))
 		return -ENOMEM;
 
@@ -1291,7 +1292,7 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
 	head = n;
 	tail = 0;
 
-	kvfree(pipe->bufs);
+	kfree(pipe->bufs);
 	pipe->bufs = bufs;
 	pipe->ring_size = nr_slots;
 	if (pipe->max_usage > nr_slots)