[PATCH V6 03/10] fork: add USER_WORKER flag to not dup/clone files
STALE1759d
REVIEWED: 5 (4M)
From: Mike Christie <michael.christie@oracle.com>
Date: 2021-11-29 19:50:11
Also in:
lkml
Subsystem:
exec & binfmt api, elf, memory management - core, scheduler, the rest · Maintainers:
Kees Cook, Andrew Morton, David Hildenbrand, Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot, Linus Torvalds
2 review trailers.
Each vhost device gets a thread that is used to perform IO and management
operations. Instead of a thread that is accessing a device, the thread is
part of the device, so when it calls the user_worker() function added in
the next patch we can't dup or clone the parent's files/FDS because it
would do an extra increment on ourself.
Later, when we do:
Qemu process exits:
do_exit -> exit_files -> put_files_struct -> close_files
we would leak the device's resources because of that extra refcount
on the fd or file_struct.
This patch adds a no_files option so these worker threads can prevent
taking an extra refcount on themselves.
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Acked-by: Christian Brauner <redacted>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
include/linux/sched/task.h | 1 +
kernel/fork.c | 11 +++++++++--
2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index b7861cb6a74b..e094502b2eea 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h@@ -20,6 +20,7 @@ struct css_set; #define USER_WORKER BIT(0) #define USER_WORKER_IO BIT(1) +#define USER_WORKER_NO_FILES BIT(2) struct kernel_clone_args { u64 flags;
diff --git a/kernel/fork.c b/kernel/fork.c
index 0d278ac26f2f..a47bec00f37c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c@@ -1529,7 +1529,8 @@ static int copy_fs(unsigned long clone_flags, struct task_struct *tsk) return 0; } -static int copy_files(unsigned long clone_flags, struct task_struct *tsk) +static int copy_files(unsigned long clone_flags, struct task_struct *tsk, + int no_files) { struct files_struct *oldf, *newf; int error = 0;
@@ -1541,6 +1542,11 @@ static int copy_files(unsigned long clone_flags, struct task_struct *tsk) if (!oldf) goto out; + if (no_files) { + tsk->files = NULL; + goto out; + } + if (clone_flags & CLONE_FILES) { atomic_inc(&oldf->count); goto out;
@@ -2179,7 +2185,8 @@ static __latent_entropy struct task_struct *copy_process( retval = copy_semundo(clone_flags, p); if (retval) goto bad_fork_cleanup_security; - retval = copy_files(clone_flags, p); + retval = copy_files(clone_flags, p, + args->worker_flags & USER_WORKER_NO_FILES); if (retval) goto bad_fork_cleanup_semundo; retval = copy_fs(clone_flags, p);
--
2.25.1
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization