[PATCH] memcg: charge io_uring related objects

[Yutian Yang <nglaive@gmail.com>]

This patch adds accounting flags to allocations of io_uring related 
objects. Allocations of the objects are all triggerable by 
io_uring_setup() syscall from userspace.

We have written a PoC to show that the missing-charging objects lead to
breaking memcg limits. The PoC program takes around 835MB unaccounted 
memory, while it is charged for only 23MB memory usage. We evaluate the 
PoC on QEMU x86_64 v5.2.90 + Linux kernel v5.10.19 + Debian buster. All 
the limitations including ulimits and sysctl variables are set as default.
Specifically, the MEMLOCK in prlimit is set as 65536KB and hard limit of 
NOFILE is set as 1,048,576.

The PoC is written as a testcase under Linux LTP. To compile it, put the 
source to ltp_dir/testcases/kernel/syscalls/io_uring/ and make.

/*------------------------- POC code ----------------------------*/

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include "config.h"
#include "tst_test.h"
#include "lapi/io_uring.h"
#include "lapi/namespaces_constants.h"

#define TEST_FILE "test_file"

#define QUEUE_DEPTH 1
#define BLOCK_SZ    1024

#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE);  \
                        } while (0)

#define STACK_SIZE (16 * 1024)

static char thread_stack[512][STACK_SIZE];

int thread_fn(void* arg)
{
  struct io_uring_params p;
  memset(&p, 0 ,sizeof(p));
  for (int i = 0; i< 10000 ; ++i) {
    int ringfd = io_uring_setup(QUEUE_DEPTH, &p);
    if (ringfd == -1) {
      errExit("io_uring_setup");
    }
  }
  while(1);
  return 0;
}

static void run(unsigned int n) {
  int thread_pid;
  for (int i = 0; i < 1; ++i) {
    thread_pid = ltp_clone(SIGCHLD, thread_fn, NULL, STACK_SIZE, \
      thread_stack[i]);
  }
  while(1);
}

static struct tst_test test = {
  .test = run,
  .tcnt = 1,
  .timeout = -1,
};

/*-------------------------- end --------------------------------*/


Signed-off-by: Yutian Yang <nglaive@gmail.com>
---
 fs/io-wq.c    |  6 +++---
 fs/io_uring.c | 10 +++++-----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index f72d53848..ab31d01cc 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -1086,11 +1086,11 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
 	if (WARN_ON_ONCE(!data->free_work || !data->do_work))
 		return ERR_PTR(-EINVAL);
 
-	wq = kzalloc(sizeof(*wq), GFP_KERNEL);
+	wq = kzalloc(sizeof(*wq), GFP_KERNEL_ACCOUNT);
 	if (!wq)
 		return ERR_PTR(-ENOMEM);
 
-	wq->wqes = kcalloc(nr_node_ids, sizeof(struct io_wqe *), GFP_KERNEL);
+	wq->wqes = kcalloc(nr_node_ids, sizeof(struct io_wqe *), GFP_KERNEL_ACCOUNT);
 	if (!wq->wqes)
 		goto err_wq;
 
@@ -1111,7 +1111,7 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
 
 		if (!node_online(alloc_node))
 			alloc_node = NUMA_NO_NODE;
-		wqe = kzalloc_node(sizeof(struct io_wqe), GFP_KERNEL, alloc_node);
+		wqe = kzalloc_node(sizeof(struct io_wqe), GFP_KERNEL_ACCOUNT, alloc_node);
 		if (!wqe)
 			goto err;
 		wq->wqes[node] = wqe;
diff --git a/fs/io_uring.c b/fs/io_uring.c
index d0b7332ca..175fd5b0e 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1177,7 +1177,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	struct io_ring_ctx *ctx;
 	int hash_bits;
 
-	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
 	if (!ctx)
 		return NULL;
 
@@ -1195,7 +1195,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 		hash_bits = 1;
 	ctx->cancel_hash_bits = hash_bits;
 	ctx->cancel_hash = kmalloc((1U << hash_bits) * sizeof(struct hlist_head),
-					GFP_KERNEL);
+					GFP_KERNEL_ACCOUNT);
 	if (!ctx->cancel_hash)
 		goto err;
 	__hash_init(ctx->cancel_hash, 1U << hash_bits);
@@ -7850,7 +7850,7 @@ static int io_uring_alloc_task_context(struct task_struct *task)
 	struct io_uring_task *tctx;
 	int ret;
 
-	tctx = kmalloc(sizeof(*tctx), GFP_KERNEL);
+	tctx = kmalloc(sizeof(*tctx), GFP_KERNEL_ACCOUNT);
 	if (unlikely(!tctx))
 		return -ENOMEM;
 
@@ -8038,7 +8038,7 @@ static void io_mem_free(void *ptr)
 
 static void *io_mem_alloc(size_t size)
 {
-	gfp_t gfp_flags = GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP |
+	gfp_t gfp_flags = GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP |
 				__GFP_NORETRY;
 
 	return (void *) __get_free_pages(gfp_flags, get_order(size));
@@ -9874,7 +9874,7 @@ static int __init io_uring_init(void)
 
 	BUILD_BUG_ON(ARRAY_SIZE(io_op_defs) != IORING_OP_LAST);
 	BUILD_BUG_ON(__REQ_F_LAST_BIT >= 8 * sizeof(int));
-	req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
+	req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
 	return 0;
 };
 __initcall(io_uring_init);
-- 
2.25.1