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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 Acked-by: Christian Brauner Reviewed-by: Christoph Hellwig --- 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 9e20fa18c41f..7f6364e5aa1a 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 19293bcca001..43213bc926c6 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1600,7 +1600,8 @@ 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; @@ -1612,6 +1613,11 @@ static int copy_files(unsigned long clone_flags, struct task_struct *tsk) if (!oldf) goto out; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" 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 Acked-by: Christian Brauner Reviewed-by: Christoph Hellwig --- 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 9e20fa18c41f..7f6364e5aa1a 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 19293bcca001..43213bc926c6 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1600,7 +1600,8 @@ 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; @@ -1612,6 +1613,11 @@ 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; @@ -2226,7 +2232,8 @@ 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