From d0bd587a80960d7ba7e0c8396e154028c9045c54 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Fri, 23 Mar 2012 15:02:47 -0700 Subject: usermodehelper: implement UMH_KILLABLE 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 --- include/linux/kmod.h | 2 ++ kernel/kmod.c | 27 +++++++++++++++++++++++++-- 2 files changed, 27 insertions(+), 2 deletions(-) diff --git a/include/linux/kmod.h b/include/linux/kmod.h index 722f477c4ef7..1b5985855ffc 100644 --- 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; diff --git a/kernel/kmod.c b/kernel/kmod.c index 8ea25944ce33..f92f917c450c 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -201,7 +201,15 @@ EXPORT_SYMBOL(call_usermodehelper_freeinfo); 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. */ @@ -252,6 +260,9 @@ static void __call_usermodehelper(struct work_struct *work) 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. */ @@ -461,9 +472,21 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, 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: -- cgit v1.2.3