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 creates a thread using a helper based on
copy_process 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@xxxxxxxxxx>
Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---
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 0467b3ce1c94..706ca3dc3423 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 1f6e7184b31f..81a1096d6ee9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1530,7 +1530,8 @@ 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;
@@ -1542,6 +1543,11 @@ 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;
@@ -2153,7 +2159,8 @@ 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
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