Hi,
Le jeudi 05 décembre 2013 à 16:23 -0500, David Miller a écrit :
> From: Yann Droneaud <[email protected]>
> Date: Mon, 2 Dec 2013 11:12:26 +0100
>
> > socketpair() error paths can be simplified to not call
> > heavy-weight sys_close().
> >
> > This patch makes socketpair() use of error paths which do not
> > rely on heavy-weight call to sys_lose(): it's better to try
> > to push the file descriptor to userspace before installing
> > the socket file to the file descriptor, so that errors are
> > catched earlier and being easier to handle.
> >
> > Three distinct error paths are needed since calling fput()
> > on file structure returned by sock_alloc_file() will
> > implicitly call sock_release() on the associated socket
> > structure.
> >
> > Cc: David S. Miller <[email protected]>
> > Cc: Al Viro <[email protected]>
> > Signed-off-by: Yann Droneaud <[email protected]>
> > Link:
> > http://marc.info/[email protected]
>
> I know that sys_close() is expensive, _but_ erroring out on
> the put_user() is extremely rare and logically it makes
> a ton more sense to fully install a file descriptor before
> writing it's numeric value into userspace.
>
> Sorry, I think the current code is fine and I'm not going
> to apply this, thanks.
Thanks for the review.
AFAIK, using sys_close() seems to be the exception, and writing the file
descriptor before installing it is the more or less the norm.
I've made a review of each subsystem using get_unused_fd{,_flags} and
anon_inode_get{fd,file}: most of the time, error handling involve fput()
and put_unused_fd() and not sys_close().
Looking at the places where sys_close() is used make it pretty obvious:
- autofs_dev_ioctl_closemount(), dev-ioctl.c:298 [1]
[just a "fancy" way of doing close() through an ioctl]
- load_misc_binary(), binfmt_misc.c:208 [2]
[could probably made use fput(),put_unused_fd()]
- change_floppy(), do_mounts.c:490,501 [3]
- handle_initrd(), do_mounts_initrd.c:113 [4]
- md_setup_drive(), do_mounts_md.c:193,245,249 [5]
- autodetect_raid(), do_mounts_md.c:299 [6]
- rd_load_image(), do_mounts_rd.c:266,292,294 [7]
- do_copy(), initramfs.c:350 [8]
- clean_rootfs(), initramfs.c:549,577 [9]
- populate_rootfs(), initramfs.c:607 [10]
- socketpair(), socket.c:1486,1487 [11]
[our target]
The majority of sys_close() users are in init code, which is code
behaving like userspace code.
This make socketpair() usage of sys_close() quite unusual.
It deserve to be replaced by the more common pattern of fput() /
put_unused_fd().
Regards.
Links:
[1]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/autofs4/dev-ioctl.c?id=v3.13-rc2#n298
[2]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/binfmt_misc.c?id=v3.13-rc2#n208
[3]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/do_mounts.c?id=v3.13-rc2#n490
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/do_mounts.c?id=v3.13-rc2#n501
[4]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/do_mounts_initrd.c?id=v3.13-rc2#n113
[5]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/do_mounts_md.c?id=v3.13-rc2#n193
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/do_mounts_md.c?id=v3.13-rc2#n245
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/do_mounts_md.c?id=v3.13-rc2#n249
[6]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/do_mounts_md.c?id=v3.13-rc2#n299
[7]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/do_mounts_rd.c?id=v3.13-rc2#n266
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/do_mounts_rd.c?id=v3.13-rc2#n292
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/do_mounts_rd.c?id=v3.13-rc2#n294
[8]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/initramfs.c?id=v3.13-rc2#n350
[9]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/initramfs.c?id=v3.13-rc2#n549
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/initramfs.c?id=v3.13-rc2#n577
[10]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/init/initramfs.c?id=v3.13-rc2#n607
[11]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/net/socket.c?id=v3.13-rc2#n1486
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/net/socket.c?id=v3.13-rc2#n1487
Aside: I will submit "soon" a patchset that add some sys_close() in
error paths of code relying on anon_inode_getfd() or using some layer
which call get_unused_fd{,flags}()/fd_install() deep in the call chain,
mostly in kvm, drm, iio.
Regards.
--
Yann Droneaud
OPTEYA
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
