Re: [PATCH v2] coredump: exit_files() in coredump_wait() if MMF_DUMP_MAPPED_SHARED is not set

[Pedro Falcato <pfalcato@suse.de>]

On Thu, Jun 18, 2026 at 11:03:01PM +0800, Xin Zhao wrote:
> A coredump typically takes some time to complete. If we happen to hold a
> write lock with flock just before triggering the coredump, that write lock
> will not be released during the entire coredump process. As a result,
> other processes attempting to acquire the same write lock may experience
> significant delays.
> 
> To address this, call exit_files() in the end of coredump_wait(), if
> MMF_DUMP_MAPPED_SHARED is not set.
> 
> Signed-off-by: Xin Zhao <jackzxcui1989@163.com>
> ---
> 
> Change in v2:
> - Get rid of the implement of adding new fcntl API, the issue does not
>   worth inflicting the cost on everyone,
>   as suggested by Al Viro.
> - Call exit_files() in coredump_wait(),
>   as suggested by Eric W. Biederman.
>   Add MMF_DUMP_MAPPED_SHARED mm_flags_test() check to filter cases that
>   need to dump file-backed shared memory.
> 
> v1:
> - Link to v1: https://lore.kernel.org/all/20260618030700.2511668-1-jackzxcui1989@163.com/
> ---
>  fs/coredump.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/coredump.c b/fs/coredump.c
> index bb6fdb1f4..e20baf44f 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -548,6 +548,9 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
>  		}
>  	}
>  
> +	if (!mm_flags_test(MMF_DUMP_MAPPED_SHARED, tsk->mm))
> +		exit_files(tsk);

Memory mapped files keep their own separate references to the files
(in struct vm_area_struct::vm_file), so there is no need to attempt to
work around this. Unless I'm misunderstanding what you're attempting
to work around.


-- 
Pedro