Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755406Ab1BUARi (ORCPT ); Sun, 20 Feb 2011 19:17:38 -0500 Received: from 184-106-158-135.static.cloud-ips.com ([184.106.158.135]:48291 "EHLO mail" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753864Ab1BUARh (ORCPT ); Sun, 20 Feb 2011 19:17:37 -0500 Date: Mon, 21 Feb 2011 00:17:43 +0000 From: "Serge E. Hallyn" To: Oleg Nesterov Cc: Andrew Morton , Daniel Lezcano , containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, ebiederm@xmission.com, KOSAKI Motohiro , Alexey Dobriyan , xemul@openvz.org Subject: Re: [PATCH 1/1][3rd resend] sys_unshare: remove the dead CLONE_THREAD/SIGHAND/VM code Message-ID: <20110221001743.GA3627@mail.hallyn.com> References: <1297788824-20534-1-git-send-email-daniel.lezcano@free.fr> <1297788824-20534-2-git-send-email-daniel.lezcano@free.fr> <20110215190118.GA16707@redhat.com> <20110215191521.GB16707@redhat.com> <20110215191711.GC16707@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110215191711.GC16707@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7650 Lines: 238 Quoting Oleg Nesterov (oleg@redhat.com): > Cleanup: kill the dead code which does nothing but complicates the code > and confuses the reader. > > sys_unshare(CLONE_THREAD/SIGHAND/VM) is not really implemented, and I doubt > very much it will ever work. At least, nobody even tried since the original > "unshare system call -v5: system call handler function" commit > 99d1419d96d7df9cfa56bc977810be831bd5ef64 was applied more than 4 years ago. > > And the code is not consistent. unshare_thread() always fails unconditionally, > while unshare_sighand() and unshare_vm() pretend to work if there is nothing > to unshare. > > Remove unshare_thread(), unshare_sighand(), unshare_vm() helpers and related > variables and add a simple CLONE_THREAD | CLONE_SIGHAND| CLONE_VM check into > check_unshare_flags(). > > Also, move the "CLONE_NEWNS needs CLONE_FS" check from check_unshare_flags() > to sys_unshare(). This looks more consistent and matches the similar > do_sysvsem check in sys_unshare(). > > Note: with or without this patch "atomic_read(mm->mm_users) > 1" can give > a false positive due to get_task_mm(). > > Signed-off-by: Oleg Nesterov > Acked-by: Roland McGrath Yes, please. Acked-by: Serge Hallyn thanks, -serge > --- > > kernel/fork.c | 123 +++++++++++----------------------------------------------- > 1 file changed, 25 insertions(+), 98 deletions(-) > > --- 2.6.37/kernel/fork.c~unshare-killcrap 2010-11-05 18:03:28.000000000 +0100 > +++ 2.6.37/kernel/fork.c 2010-11-05 18:09:52.000000000 +0100 > @@ -1522,38 +1522,24 @@ void __init proc_caches_init(void) > } > > /* > - * Check constraints on flags passed to the unshare system call and > - * force unsharing of additional process context as appropriate. > + * Check constraints on flags passed to the unshare system call. > */ > -static void check_unshare_flags(unsigned long *flags_ptr) > +static int check_unshare_flags(unsigned long unshare_flags) > { > + if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND| > + CLONE_VM|CLONE_FILES|CLONE_SYSVSEM| > + CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET)) > + return -EINVAL; > /* > - * If unsharing a thread from a thread group, must also > - * unshare vm. > - */ > - if (*flags_ptr & CLONE_THREAD) > - *flags_ptr |= CLONE_VM; > - > - /* > - * If unsharing vm, must also unshare signal handlers. > - */ > - if (*flags_ptr & CLONE_VM) > - *flags_ptr |= CLONE_SIGHAND; > - > - /* > - * If unsharing namespace, must also unshare filesystem information. > + * Not implemented, but pretend it works if there is nothing to > + * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND > + * needs to unshare vm. > */ > - if (*flags_ptr & CLONE_NEWNS) > - *flags_ptr |= CLONE_FS; > -} > - > -/* > - * Unsharing of tasks created with CLONE_THREAD is not supported yet > - */ > -static int unshare_thread(unsigned long unshare_flags) > -{ > - if (unshare_flags & CLONE_THREAD) > - return -EINVAL; > + if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) { > + /* FIXME: get_task_mm() increments ->mm_users */ > + if (atomic_read(¤t->mm->mm_users) > 1) > + return -EINVAL; > + } > > return 0; > } > @@ -1580,34 +1566,6 @@ static int unshare_fs(unsigned long unsh > } > > /* > - * Unsharing of sighand is not supported yet > - */ > -static int unshare_sighand(unsigned long unshare_flags, struct sighand_struct **new_sighp) > -{ > - struct sighand_struct *sigh = current->sighand; > - > - if ((unshare_flags & CLONE_SIGHAND) && atomic_read(&sigh->count) > 1) > - return -EINVAL; > - else > - return 0; > -} > - > -/* > - * Unshare vm if it is being shared > - */ > -static int unshare_vm(unsigned long unshare_flags, struct mm_struct **new_mmp) > -{ > - struct mm_struct *mm = current->mm; > - > - if ((unshare_flags & CLONE_VM) && > - (mm && atomic_read(&mm->mm_users) > 1)) { > - return -EINVAL; > - } > - > - return 0; > -} > - > -/* > * Unshare file descriptor table if it is being shared > */ > static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp) > @@ -1635,45 +1593,37 @@ static int unshare_fd(unsigned long unsh > */ > SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) > { > - int err = 0; > struct fs_struct *fs, *new_fs = NULL; > - struct sighand_struct *new_sigh = NULL; > - struct mm_struct *mm, *new_mm = NULL, *active_mm = NULL; > struct files_struct *fd, *new_fd = NULL; > struct nsproxy *new_nsproxy = NULL; > int do_sysvsem = 0; > + int err; > > - check_unshare_flags(&unshare_flags); > - > - /* Return -EINVAL for all unsupported flags */ > - err = -EINVAL; > - if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND| > - CLONE_VM|CLONE_FILES|CLONE_SYSVSEM| > - CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET)) > + err = check_unshare_flags(unshare_flags); > + if (err) > goto bad_unshare_out; > > /* > + * If unsharing namespace, must also unshare filesystem information. > + */ > + if (unshare_flags & CLONE_NEWNS) > + unshare_flags |= CLONE_FS; > + /* > * CLONE_NEWIPC must also detach from the undolist: after switching > * to a new ipc namespace, the semaphore arrays from the old > * namespace are unreachable. > */ > if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM)) > do_sysvsem = 1; > - if ((err = unshare_thread(unshare_flags))) > - goto bad_unshare_out; > if ((err = unshare_fs(unshare_flags, &new_fs))) > - goto bad_unshare_cleanup_thread; > - if ((err = unshare_sighand(unshare_flags, &new_sigh))) > - goto bad_unshare_cleanup_fs; > - if ((err = unshare_vm(unshare_flags, &new_mm))) > - goto bad_unshare_cleanup_sigh; > + goto bad_unshare_out; > if ((err = unshare_fd(unshare_flags, &new_fd))) > - goto bad_unshare_cleanup_vm; > + goto bad_unshare_cleanup_fs; > if ((err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy, > new_fs))) > goto bad_unshare_cleanup_fd; > > - if (new_fs || new_mm || new_fd || do_sysvsem || new_nsproxy) { > + if (new_fs || new_fd || do_sysvsem || new_nsproxy) { > if (do_sysvsem) { > /* > * CLONE_SYSVSEM is equivalent to sys_exit(). > @@ -1699,19 +1649,6 @@ SYSCALL_DEFINE1(unshare, unsigned long, > spin_unlock(&fs->lock); > } > > - if (new_mm) { > - mm = current->mm; > - active_mm = current->active_mm; > - current->mm = new_mm; > - current->active_mm = new_mm; > - if (current->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) { > - atomic_dec(&mm->oom_disable_count); > - atomic_inc(&new_mm->oom_disable_count); > - } > - activate_mm(active_mm, new_mm); > - new_mm = mm; > - } > - > if (new_fd) { > fd = current->files; > current->files = new_fd; > @@ -1728,20 +1665,10 @@ bad_unshare_cleanup_fd: > if (new_fd) > put_files_struct(new_fd); > > -bad_unshare_cleanup_vm: > - if (new_mm) > - mmput(new_mm); > - > -bad_unshare_cleanup_sigh: > - if (new_sigh) > - if (atomic_dec_and_test(&new_sigh->count)) > - kmem_cache_free(sighand_cachep, new_sigh); > - > bad_unshare_cleanup_fs: > if (new_fs) > free_fs_struct(new_fs); > > -bad_unshare_cleanup_thread: > bad_unshare_out: > return err; > } > > _______________________________________________ > Containers mailing list > Containers@lists.linux-foundation.org > https://lists.linux-foundation.org/mailman/listinfo/containers -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/