poweroff: change orderly_poweroff() to use schedule_work()

David said:

    Commit 6c0c0d4d1080 ("poweroff: fix bug in orderly_poweroff()")
    apparently fixes one bug in orderly_poweroff(), but introduces
    another.  The comments on orderly_poweroff() claim it can be called
    from any context - and indeed we call it from interrupt context in
    arch/powerpc/platforms/pseries/ras.c for example.  But since that
    commit this is no longer safe, since call_usermodehelper_fns() is not
    safe in interrupt context without the UMH_NO_WAIT option.

orderly_poweroff() can be used from any context but UMH_WAIT_EXEC is
sleepable.  Move the "force" logic into __orderly_poweroff() and change
orderly_poweroff() to use the global poweroff_work which simply calls
__orderly_poweroff().

While at it, remove the unneeded "int argc" and change argv_split() to
use GFP_KERNEL.

We use the global "bool poweroff_force" to pass the argument, this can
obviously affect the previous request if it is pending/running.  So we
only allow the "false => true" transition assuming that the pending
"true" should succeed anyway.  If schedule_work() fails after that we
know that work->func() was not called yet, it must see the new value.

This means that orderly_poweroff() becomes async even if we do not run
the command and always succeeds, schedule_work() can only fail if the
work is already pending.  We can export __orderly_poweroff() and change
the non-atomic callers which want the old semantics.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reported-by: David Gibson <david@gibson.dropbear.id.au>
Cc: Lucas De Marchi <lucas.demarchi@profusion.mobi>
Cc: Feng Hong <hongfeng@marvell.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/sys.c b/kernel/sys.c
index 81f5644..39c9c4a 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2185,9 +2185,8 @@ SYSCALL_DEFINE3(getcpu, unsigned __user *, cpup, unsigned __user *, nodep,
 
 char poweroff_cmd[POWEROFF_CMD_PATH_LEN] = "/sbin/poweroff";
 
-static int __orderly_poweroff(void)
+static int __orderly_poweroff(bool force)
 {
-       int argc;
        char **argv;
        static char *envp[] = {
                "HOME=/",
@@ -2196,20 +2195,40 @@ static int __orderly_poweroff(void)
        };
        int ret;
 
-       argv = argv_split(GFP_ATOMIC, poweroff_cmd, &argc);
-       if (argv == NULL) {
+       argv = argv_split(GFP_KERNEL, poweroff_cmd, NULL);
+       if (argv) {
+               ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
+               argv_free(argv);
+       } else {
                printk(KERN_WARNING "%s failed to allocate memory for \"%s\"\n",
-                      __func__, poweroff_cmd);
-               return -ENOMEM;
+                                        __func__, poweroff_cmd);
+               ret = -ENOMEM;
        }
 
-       ret = call_usermodehelper_fns(argv[0], argv, envp, UMH_WAIT_EXEC,
-                                     NULL, NULL, NULL);
-       argv_free(argv);
+       if (ret && force) {
+               printk(KERN_WARNING "Failed to start orderly shutdown: "
+                                       "forcing the issue\n");
+               /*
+                * I guess this should try to kick off some daemon to sync and
+                * poweroff asap.  Or not even bother syncing if we're doing an
+                * emergency shutdown?
+                */
+               emergency_sync();
+               kernel_power_off();
+       }
 
        return ret;
 }
 
+static bool poweroff_force;
+
+static void poweroff_work_func(struct work_struct *work)
+{
+       __orderly_poweroff(poweroff_force);
+}
+
+static DECLARE_WORK(poweroff_work, poweroff_work_func);
+
 /**
  * orderly_poweroff - Trigger an orderly system poweroff
  * @force: force poweroff if command execution fails
@@ -2219,21 +2238,9 @@ static int __orderly_poweroff(void)
  */
 int orderly_poweroff(bool force)
 {
-       int ret = __orderly_poweroff();
-
-       if (ret && force) {
-               printk(KERN_WARNING "Failed to start orderly shutdown: "
-                      "forcing the issue\n");
-
-               /*
-                * I guess this should try to kick off some daemon to sync and
-                * poweroff asap.  Or not even bother syncing if we're doing an
-                * emergency shutdown?
-                */
-               emergency_sync();
-               kernel_power_off();
-       }
-
-       return ret;
+       if (force) /* do not override the pending "true" */
+               poweroff_force = true;
+       schedule_work(&poweroff_work);
+       return 0;
 }
 EXPORT_SYMBOL_GPL(orderly_poweroff);