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Date: Mon, 19 Aug 2013 21:53:10 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Al Viro <viro@...IV.linux.org.uk>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
Davide Libenzi <davidel@...ilserver.org>,
Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] vfio-pci: PCI hot reset interface
On Tue, 2013-08-20 at 04:18 +0100, Al Viro wrote:
> On Wed, Aug 14, 2013 at 04:42:14PM -0600, Bjorn Helgaas wrote:
> > [+cc Al, linux-fsdevel for fdget/fdput usage]
>
> fdget/fdput use looks sane, the only thing is that I would rather
> have an explicit include of linux/file.h instead of relying upon
> linux/eventfd.h pulling it.
Thanks for reviewing, I'll add an explicit include.
> Incidentally, there are only 5 files
> that include the latter without an explicit include of the former -
> drivers/vfio/pci/vfio_pci.c, drivers/vhost/scsi.c, kernel/cgroup.c,
> mm/memcontrol.c and mm/vmpressure.c. And only kernel/cgroup.c (and,
> with this patch, vfio_pci.c) really wants anything from linux/file.h,
> so I'd rather kill that indirect include in eventfd.h and slapped
> an explicit include of file.h in these two files...
>
> BTW, most of the eventfd_fget() users might as well be using fget()
> (or fdget(), for that matter). They tend to be immediately followed
> by eventfd_ctx_fileget(), which repeats the "is that an eventfd file?"
> check anyway.
Hmm, I've got one of those elsewhere in vfio code too. Thanks for the
tip.
Alex
> Completely untested patch below does that to kernel/cgroup.c; Tejun,
> Davide - do you have any objections against the following?
>
> Kill indirect include of file.h from eventfd.h, use fdget() in cgroup.c
>
> kernel/cgroup.c is the only place in the tree that relies on eventfd.h
> pulling file.h; move that include there. Switch from eventfd_fget()/fput()
> to fdget()/fdput(), while we are at it - eventfd_ctx_fileget() will fail
> on non-eventfd descriptors just fine, no need to do that check twice...
>
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---
> diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h
> index cf5d2af..ff0b981 100644
> --- a/include/linux/eventfd.h
> +++ b/include/linux/eventfd.h
> @@ -9,7 +9,6 @@
> #define _LINUX_EVENTFD_H
>
> #include <linux/fcntl.h>
> -#include <linux/file.h>
> #include <linux/wait.h>
>
> /*
> @@ -26,6 +25,8 @@
> #define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK)
> #define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE)
>
> +struct file;
> +
> #ifdef CONFIG_EVENTFD
>
> struct file *eventfd_file_create(unsigned int count, int flags);
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 781845a..f88ecaf 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -60,6 +60,7 @@
> #include <linux/poll.h>
> #include <linux/flex_array.h> /* used in cgroup_attach_task */
> #include <linux/kthread.h>
> +#include <linux/file.h>
>
> #include <linux/atomic.h>
>
> @@ -3969,8 +3970,8 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
> struct cgroup_event *event = NULL;
> struct cgroup *cgrp_cfile;
> unsigned int efd, cfd;
> - struct file *efile = NULL;
> - struct file *cfile = NULL;
> + struct fd efile;
> + struct fd cfile;
> char *endp;
> int ret;
>
> @@ -3993,31 +3994,31 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
> init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
> INIT_WORK(&event->remove, cgroup_event_remove);
>
> - efile = eventfd_fget(efd);
> - if (IS_ERR(efile)) {
> - ret = PTR_ERR(efile);
> - goto fail;
> + efile = fdget(efd);
> + if (!efile.file) {
> + ret = -EBADF;
> + goto fail1;
> }
>
> - event->eventfd = eventfd_ctx_fileget(efile);
> + event->eventfd = eventfd_ctx_fileget(efile.file);
> if (IS_ERR(event->eventfd)) {
> ret = PTR_ERR(event->eventfd);
> - goto fail;
> + goto fail2;
> }
>
> - cfile = fget(cfd);
> - if (!cfile) {
> + cfile = fdget(cfd);
> + if (!cfile.file) {
> ret = -EBADF;
> - goto fail;
> + goto fail3;
> }
>
> /* the process need read permission on control file */
> /* AV: shouldn't we check that it's been opened for read instead? */
> - ret = inode_permission(file_inode(cfile), MAY_READ);
> + ret = inode_permission(file_inode(cfile.file), MAY_READ);
> if (ret < 0)
> goto fail;
>
> - event->cft = __file_cft(cfile);
> + event->cft = __file_cft(cfile.file);
> if (IS_ERR(event->cft)) {
> ret = PTR_ERR(event->cft);
> goto fail;
> @@ -4027,7 +4028,7 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
> * The file to be monitored must be in the same cgroup as
> * cgroup.event_control is.
> */
> - cgrp_cfile = __d_cgrp(cfile->f_dentry->d_parent);
> + cgrp_cfile = __d_cgrp(cfile.file->f_dentry->d_parent);
> if (cgrp_cfile != cgrp) {
> ret = -EINVAL;
> goto fail;
> @@ -4043,7 +4044,7 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
> if (ret)
> goto fail;
>
> - efile->f_op->poll(efile, &event->pt);
> + efile.file->f_op->poll(efile.file, &event->pt);
>
> /*
> * Events should be removed after rmdir of cgroup directory, but before
> @@ -4056,21 +4057,18 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
> list_add(&event->list, &cgrp->event_list);
> spin_unlock(&cgrp->event_list_lock);
>
> - fput(cfile);
> - fput(efile);
> + fdput(cfile);
> + fdput(efile);
>
> return 0;
>
> fail:
> - if (cfile)
> - fput(cfile);
> -
> - if (event && event->eventfd && !IS_ERR(event->eventfd))
> - eventfd_ctx_put(event->eventfd);
> -
> - if (!IS_ERR_OR_NULL(efile))
> - fput(efile);
> -
> + fdput(cfile);
> +fail3:
> + eventfd_ctx_put(event->eventfd);
> +fail2:
> + fdput(efile);
> +fail1:
> kfree(event);
>
> return ret;
> --
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