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usermodehelper: implement UMH_KILLABLE

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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 <oleg@redhat.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2012-03-23 15:02:47 -07:00 committed by Linus Torvalds
parent b344992250
commit d0bd587a80
2 changed files with 28 additions and 3 deletions
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2
include/linux/kmod.h
View file

@ -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;

29
kernel/kmod.c
View file

@ -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;
wait_for_completion(&done);
retval = sub_info->retval;
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: