Messages in this thread | | | Subject | Re: [PATCH v2] net: handle error more gracefully in socketpair() | From | Yann Droneaud <> | Date | Fri, 06 Dec 2013 00:15:31 +0100 |
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Hi,
Le jeudi 05 décembre 2013 à 16:23 -0500, David Miller a écrit : > From: Yann Droneaud <ydroneaud@opteya.com> > 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 <davem@davemloft.net> > > Cc: Al Viro <viro@zeniv.linux.org.uk> > > Signed-off-by: Yann Droneaud <ydroneaud@opteya.com> > > Link: http://marc.info/?i=1385977019-12282-1-git-send-email-ydroneaud@opteya.com > > 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
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