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 <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>
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2 changed files with 28 additions and 3 deletions
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@ -54,6 +54,8 @@ enum umh_wait {
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UMH_WAIT_PROC = 1, /* wait for the process to complete */
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UMH_WAIT_PROC = 1, /* wait for the process to complete */
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};
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};
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#define UMH_KILLABLE 4 /* wait for EXEC/PROC killable */
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struct subprocess_info {
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struct subprocess_info {
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struct work_struct work;
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struct work_struct work;
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struct completion *complete;
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struct completion *complete;
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@ -201,7 +201,15 @@ EXPORT_SYMBOL(call_usermodehelper_freeinfo);
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static void umh_complete(struct subprocess_info *sub_info)
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static void umh_complete(struct subprocess_info *sub_info)
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{
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{
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complete(sub_info->complete);
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struct completion *comp = xchg(&sub_info->complete, NULL);
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/*
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* See call_usermodehelper_exec(). If xchg() returns NULL
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* we own sub_info, the UMH_KILLABLE caller has gone away.
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*/
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if (comp)
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complete(comp);
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else
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call_usermodehelper_freeinfo(sub_info);
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}
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}
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/* Keventd can't block, but this (a child) can. */
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/* Keventd can't block, but this (a child) can. */
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@ -252,6 +260,9 @@ static void __call_usermodehelper(struct work_struct *work)
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enum umh_wait wait = sub_info->wait;
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enum umh_wait wait = sub_info->wait;
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pid_t pid;
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pid_t pid;
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if (wait != UMH_NO_WAIT)
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wait &= ~UMH_KILLABLE;
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/* CLONE_VFORK: wait until the usermode helper has execve'd
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/* CLONE_VFORK: wait until the usermode helper has execve'd
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* successfully We need the data structures to stay around
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* successfully We need the data structures to stay around
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* until that is done. */
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* until that is done. */
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@ -461,9 +472,21 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info,
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queue_work(khelper_wq, &sub_info->work);
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queue_work(khelper_wq, &sub_info->work);
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if (wait == UMH_NO_WAIT) /* task has freed sub_info */
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if (wait == UMH_NO_WAIT) /* task has freed sub_info */
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goto unlock;
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goto unlock;
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wait_for_completion(&done);
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retval = sub_info->retval;
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if (wait & UMH_KILLABLE) {
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retval = wait_for_completion_killable(&done);
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if (!retval)
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goto wait_done;
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/* umh_complete() will see NULL and free sub_info */
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if (xchg(&sub_info->complete, NULL))
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goto unlock;
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/* fallthrough, umh_complete() was already called */
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}
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wait_for_completion(&done);
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wait_done:
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retval = sub_info->retval;
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out:
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out:
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call_usermodehelper_freeinfo(sub_info);
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call_usermodehelper_freeinfo(sub_info);
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unlock:
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unlock:
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