From: Mike Christie <michael.christie@oracle.com>
To: 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 <michael.christie@oracle.com>
Subject: [PATCH V2 4/9] fork: add option to not clone or dup files
Date: Tue, 21 Sep 2021 16:52:13 -0500 [thread overview]
Message-ID: <20210921215218.89844-5-michael.christie@oracle.com> (raw)
In-Reply-To: <20210921215218.89844-1-michael.christie@oracle.com>
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 <michael.christie@oracle.com>
---
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 cf7c9fffc839..e165cc67fd3c 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 4b0e8257993b..98264cf1d6a6 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;
@@ -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
next prev parent reply other threads:[~2021-09-21 21:53 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-21 21:52 [PATCH V2 0/9] Use copy_process/create_io_thread in vhost layer Mike Christie
2021-09-21 21:52 ` [PATCH V2 1/9] fork: Make IO worker options flag based Mike Christie
2021-09-22 12:44 ` Christian Brauner
2021-09-21 21:52 ` [PATCH V2 2/9] fork: pass worker_flags to copy_thread Mike Christie
2021-09-22 12:42 ` Christian Brauner
2021-09-22 14:18 ` Geert Uytterhoeven
2021-09-21 21:52 ` [PATCH V2 3/9] fork: move PF_IO_WORKER's kernel frame setup to new flag Mike Christie
2021-09-22 12:32 ` Geert Uytterhoeven
2021-09-22 12:39 ` Christian Brauner
2021-09-22 12:45 ` Christian Brauner
2021-09-21 21:52 ` Mike Christie [this message]
2021-09-22 12:46 ` [PATCH V2 4/9] fork: add option to not clone or dup files Christian Brauner
2021-09-21 21:52 ` [PATCH V2 5/9] fork: add helper to clone a process Mike Christie
2021-09-22 12:50 ` Christian Brauner
2021-09-21 21:52 ` [PATCH V2 6/9] io_uring: switch to kernel_worker Mike Christie
2021-09-22 12:53 ` Christian Brauner
2021-09-21 21:52 ` [PATCH V2 7/9] fork: Add worker flag to ignore signals Mike Christie
2021-09-22 12:52 ` Christian Brauner
2021-09-21 21:52 ` [PATCH V2 8/9] vhost: move worker thread fields to new struct Mike Christie
2021-10-04 13:12 ` Michael S. Tsirkin
2021-09-21 21:52 ` [PATCH V2 9/9] vhost: use kernel_worker to check RLIMITs and inherit v2 cgroups Mike Christie
2021-10-04 13:12 ` Michael S. Tsirkin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210921215218.89844-5-michael.christie@oracle.com \
--to=michael.christie@oracle.com \
--cc=axboe@kernel.dk \
--cc=christian.brauner@ubuntu.com \
--cc=hch@infradead.org \
--cc=hdanton@sina.com \
--cc=jasowang@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mst@redhat.com \
--cc=sgarzare@redhat.com \
--cc=stefanha@redhat.com \
--cc=virtualization@lists.linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).