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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 calls the kernel_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 Acked-by: Christian Brauner --- 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 53599a99d7e0..1153f9e5d10e 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -20,6 +20,7 @@ struct css_set; #define KERN_WORKER_IO BIT(0) #define KERN_WORKER_USER BIT(1) +#define KERN_WORKER_NO_FILES BIT(2) struct kernel_clone_args { u64 flags; diff --git a/kernel/fork.c b/kernel/fork.c index 4f780424de46..3161edac1236 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1532,7 +1532,8 @@ 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; @@ -1544,6 +1545,11 @@ 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; @@ -2181,7 +2187,8 @@ 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 & KERN_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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4F5EDC433F5 for ; Thu, 7 Oct 2021 21:45:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3016060F23 for ; 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Instead of a thread that is accessing a device, the thread is part of the device, so when it calls the kernel_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 Acked-by: Christian Brauner --- 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 53599a99d7e0..1153f9e5d10e 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -20,6 +20,7 @@ struct css_set; #define KERN_WORKER_IO BIT(0) #define KERN_WORKER_USER BIT(1) +#define KERN_WORKER_NO_FILES BIT(2) struct kernel_clone_args { u64 flags; diff --git a/kernel/fork.c b/kernel/fork.c index 4f780424de46..3161edac1236 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1532,7 +1532,8 @@ 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; @@ -1544,6 +1545,11 @@ 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; @@ -2181,7 +2187,8 @@ 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 & KERN_WORKER_NO_FILES); if (retval) goto bad_fork_cleanup_semundo; retval = copy_fs(clone_flags, p); -- 2.25.1