Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756281Ab3CDENf (ORCPT ); Sun, 3 Mar 2013 23:13:35 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:60846 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755578Ab3CDDm4 (ORCPT ); Sun, 3 Mar 2013 22:42:56 -0500 Message-Id: <20130304033721.802296788@decadent.org.uk> User-Agent: quilt/0.60-1 Date: Mon, 04 Mar 2013 03:39:32 +0000 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: akpm@linux-foundation.org, Oleg Nesterov , Tetsuo Handa , Rusty Russell , Tejun Heo , David Rientjes , Linus Torvalds Subject: [ 145/153] usermodehelper: implement UMH_KILLABLE In-Reply-To: <20130304033707.648729212@decadent.org.uk> X-SA-Exim-Connect-IP: 2001:470:1f08:1539:a11:96ff:fec6:70c4 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3562 Lines: 111 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Oleg Nesterov commit d0bd587a80960d7ba7e0c8396e154028c9045c54 upstream. Implement UMH_KILLABLE, should be used along with UMH_WAIT_EXEC/PROC. The caller must ensure that subprocess_info->path/etc can not go away until call_usermodehelper_freeinfo(). call_usermodehelper_exec(UMH_KILLABLE) does wait_for_completion_killable. If it fails, it uses xchg(&sub_info->complete, NULL) to serialize with umh_complete() which does the same xhcg() to access sub_info->complete. If call_usermodehelper_exec wins, it can safely return. umh_complete() should get NULL and call call_usermodehelper_freeinfo(). Otherwise we know that umh_complete() was already called, in this case call_usermodehelper_exec() falls back to wait_for_completion() which should succeed "very soon". Note: UMH_NO_WAIT == -1 but it obviously should not be used with UMH_KILLABLE. We delay the neccessary cleanup to simplify the back porting. Signed-off-by: Oleg Nesterov Cc: Tetsuo Handa Cc: Rusty Russell Cc: Tejun Heo Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Ben Hutchings --- include/linux/kmod.h | 2 ++ kernel/kmod.c | 27 +++++++++++++++++++++++++-- 2 files changed, 27 insertions(+), 2 deletions(-) --- a/include/linux/kmod.h +++ b/include/linux/kmod.h @@ -54,6 +54,8 @@ enum umh_wait { UMH_WAIT_PROC = 1, /* wait for the process to complete */ }; +#define UMH_KILLABLE 4 /* wait for EXEC/PROC killable */ + struct subprocess_info { struct work_struct work; struct completion *complete; --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -199,7 +199,15 @@ EXPORT_SYMBOL(call_usermodehelper_freein static void umh_complete(struct subprocess_info *sub_info) { - complete(sub_info->complete); + struct completion *comp = xchg(&sub_info->complete, NULL); + /* + * See call_usermodehelper_exec(). If xchg() returns NULL + * we own sub_info, the UMH_KILLABLE caller has gone away. + */ + if (comp) + complete(comp); + else + call_usermodehelper_freeinfo(sub_info); } /* Keventd can't block, but this (a child) can. */ @@ -250,6 +258,9 @@ static void __call_usermodehelper(struct enum umh_wait wait = sub_info->wait; pid_t pid; + if (wait != UMH_NO_WAIT) + wait &= ~UMH_KILLABLE; + /* CLONE_VFORK: wait until the usermode helper has execve'd * successfully We need the data structures to stay around * until that is done. */ @@ -440,9 +451,21 @@ int call_usermodehelper_exec(struct subp queue_work(khelper_wq, &sub_info->work); if (wait == UMH_NO_WAIT) /* task has freed sub_info */ goto unlock; + + if (wait & UMH_KILLABLE) { + retval = wait_for_completion_killable(&done); + if (!retval) + goto wait_done; + + /* umh_complete() will see NULL and free sub_info */ + if (xchg(&sub_info->complete, NULL)) + goto unlock; + /* fallthrough, umh_complete() was already called */ + } + wait_for_completion(&done); +wait_done: retval = sub_info->retval; - out: call_usermodehelper_freeinfo(sub_info); unlock: -- 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/