Re: [PATCH] memcg: charge fs_context and legacy_fs_context

[Shakeel Butt <shakeelb@google.com>]

+Andrew Morton

On Sat, Jul 17, 2021 at 3:23 AM Yutian Yang <nglaive@gmail.com> wrote:
>
> This patch adds accounting flags to fs_context and legacy_fs_context
> allocation sites so that kernel could correctly charge these objects.
>
> We have written a PoC to demonstrate the effect of the missing-charging
> bugs. The PoC takes around 1,200MB unaccounted memory, while it is charged
> for only 362MB 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 hard
> NOFILE limit and nr_open in sysctl are both 1,048,576.
>
> /*------------------------- POC code ----------------------------*/
>
> #define _GNU_SOURCE
> #include <sys/types.h>
> #include <sys/file.h>
> #include <time.h>
> #include <sys/wait.h>
> #include <stdint.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <stdio.h>
> #include <signal.h>
> #include <sched.h>
> #include <fcntl.h>
> #include <linux/mount.h>
>
> #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
>                         } while (0)
>
> #define STACK_SIZE (8 * 1024)
> #ifndef __NR_fsopen
> #define __NR_fsopen 430
> #endif
> static inline int fsopen(const char *fs_name, unsigned int flags)
> {
>         return syscall(__NR_fsopen, fs_name, flags);
> }
>
> static char thread_stack[512][STACK_SIZE];
>
> int thread_fn(void* arg)
> {
>   for (int i = 0; i< 800000; ++i) {
>     int fsfd = fsopen("nfs", FSOPEN_CLOEXEC);
>     if (fsfd == -1) {
>       errExit("fsopen");
>     }
>   }
>   while(1);
>   return 0;
> }
>
> int main(int argc, char *argv[]) {
>   int thread_pid;
>   for (int i = 0; i < 1; ++i) {
>     thread_pid = clone(thread_fn, thread_stack[i] + STACK_SIZE, \
>       SIGCHLD, NULL);
>   }
>   while(1);
>   return 0;
> }
>
> /*-------------------------- end --------------------------------*/
>
>
> Thanks!
> Yutian Yang,
> Zhejiang University
>
>
> Signed-off-by: Yutian Yang <nglaive@gmail.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>

I think this can go through the mm tree.

> ---
>  fs/fs_context.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fs_context.c b/fs/fs_context.c
> index 2834d1afa..4858645ca 100644
> --- a/fs/fs_context.c
> +++ b/fs/fs_context.c
> @@ -231,7 +231,7 @@ static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
>         struct fs_context *fc;
>         int ret = -ENOMEM;
>
> -       fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
> +       fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL_ACCOUNT);
>         if (!fc)
>                 return ERR_PTR(-ENOMEM);
>
> @@ -631,7 +631,7 @@ const struct fs_context_operations legacy_fs_context_ops = {
>   */
>  static int legacy_init_fs_context(struct fs_context *fc)
>  {
> -       fc->fs_private = kzalloc(sizeof(struct legacy_fs_context), GFP_KERNEL);
> +       fc->fs_private = kzalloc(sizeof(struct legacy_fs_context), GFP_KERNEL_ACCOUNT);
>         if (!fc->fs_private)
>                 return -ENOMEM;
>         fc->ops = &legacy_fs_context_ops;
> --
> 2.25.1
>