106 lines
3.4 KiB
Diff
106 lines
3.4 KiB
Diff
From: Oleg Nesterov <oleg@redhat.com>
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Date: Fri, 23 Mar 2012 15:02:47 -0700
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Subject: [2/5] usermodehelper: implement UMH_KILLABLE
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commit d0bd587a80960d7ba7e0c8396e154028c9045c54 upstream.
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Implement UMH_KILLABLE, should be used along with UMH_WAIT_EXEC/PROC.
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The caller must ensure that subprocess_info->path/etc can not go away
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until call_usermodehelper_freeinfo().
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call_usermodehelper_exec(UMH_KILLABLE) does
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wait_for_completion_killable. If it fails, it uses
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xchg(&sub_info->complete, NULL) to serialize with umh_complete() which
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does the same xhcg() to access sub_info->complete.
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If call_usermodehelper_exec wins, it can safely return. umh_complete()
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should get NULL and call call_usermodehelper_freeinfo().
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Otherwise we know that umh_complete() was already called, in this case
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call_usermodehelper_exec() falls back to wait_for_completion() which
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should succeed "very soon".
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Note: UMH_NO_WAIT == -1 but it obviously should not be used with
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UMH_KILLABLE. We delay the neccessary cleanup to simplify the back
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porting.
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Signed-off-by: Oleg Nesterov <oleg@redhat.com>
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Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
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Cc: Rusty Russell <rusty@rustcorp.com.au>
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Cc: Tejun Heo <tj@kernel.org>
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Cc: David Rientjes <rientjes@google.com>
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Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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include/linux/kmod.h | 2 ++
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kernel/kmod.c | 27 +++++++++++++++++++++++++--
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2 files changed, 27 insertions(+), 2 deletions(-)
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diff --git a/include/linux/kmod.h b/include/linux/kmod.h
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index 722f477..1b598585 100644
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--- a/include/linux/kmod.h
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+++ b/include/linux/kmod.h
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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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};
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+#define UMH_KILLABLE 4 /* wait for EXEC/PROC killable */
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+
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struct subprocess_info {
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struct work_struct work;
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struct completion *complete;
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diff --git a/kernel/kmod.c b/kernel/kmod.c
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index 8ea2594..f92f917 100644
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--- a/kernel/kmod.c
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+++ b/kernel/kmod.c
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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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{
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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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/* 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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pid_t pid;
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+ if (wait != UMH_NO_WAIT)
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+ wait &= ~UMH_KILLABLE;
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+
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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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* 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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if (wait == UMH_NO_WAIT) /* task has freed sub_info */
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goto unlock;
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+
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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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+
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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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+
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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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-
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out:
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call_usermodehelper_freeinfo(sub_info);
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unlock:
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