[patch 20/41] fs/pipe: use kvcalloc to allocate a pipe_buffer array

[Andrew Morton <akpm@linux-foundation.org>]

From: Andrei Vagin <avagin@gmail.com>
Subject: fs/pipe: use kvcalloc to allocate a pipe_buffer array

Right now, kcalloc is used to allocate a pipe_buffer array.  The size of
the pipe_buffer struct is 40 bytes.  kcalloc allows allocating reliably
chunks with sizes less or equal to PAGE_ALLOC_COSTLY_ORDER (3).  It means
that the maximum pipe size is 3.2MB in this case.

In CRIU, we use pipes to dump processes memory.  CRIU freezes a target
process, injects a parasite code into it and then this code splices memory
into pipes.  If a maximum pipe size is small, we need to do many
iterations or create many pipes.

kvcalloc attempt to allocate physically contiguous memory, but upon
failure, fall back to non-contiguous (vmalloc) allocation and so it isn't
limited by PAGE_ALLOC_COSTLY_ORDER.

The maximum pipe size for non-root users is limited by the
/proc/sys/fs/pipe-max-size sysctl that is 1MB by default, so only the root
user will be able to trigger vmalloc allocations.

Link: https://lkml.kernel.org/r/20220104171058.22580-1-avagin@gmail.com
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/pipe.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

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