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Sun, 21 Nov 2021 17:49:46 +0000 From: Mike Christie To: geert@linux-m68k.org, vverma@digitalocean.com, hdanton@sina.com, hch@infradead.org, stefanha@redhat.com, jasowang@redhat.com, mst@redhat.com, sgarzare@redhat.com, virtualization@lists.linux-foundation.org, christian.brauner@ubuntu.com, axboe@kernel.dk, linux-kernel@vger.kernel.org Cc: Mike Christie , Christoph Hellwig Subject: [PATCH V5 03/10] fork: add KERNEL_WORKER flag to not dup/clone files Date: Sun, 21 Nov 2021 11:49:23 -0600 Message-Id: <20211121174930.6690-4-michael.christie@oracle.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211121174930.6690-1-michael.christie@oracle.com> References: <20211121174930.6690-1-michael.christie@oracle.com> Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: CH0PR03CA0217.namprd03.prod.outlook.com (2603:10b6:610:e7::12) To DM5PR10MB1466.namprd10.prod.outlook.com (2603:10b6:3:b::7) MIME-Version: 1.0 Received: from localhost.localdomain (73.88.28.6) by CH0PR03CA0217.namprd03.prod.outlook.com (2603:10b6:610:e7::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4713.19 via Frontend Transport; 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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 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 1ad98e31d5bc..47ede41b19c5 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 8f6cd9581e2e..a1ba423eec4d 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 & KERN_WORKER_NO_FILES); if (retval) goto bad_fork_cleanup_semundo; retval = copy_fs(clone_flags, p); -- 2.25.1