[CRIU] [PATCH] lock: Restore ability to abort on futex waiting

[Cyrill Gorcunov]

In commit 71cc2733a79efba65d3466f784b19d17805cf50d
I occasionally dropped the ability to abort on waiting
(because we used signed -1 value to inform waiters that
something is wrong and waiting should be aborted, but
the type was changed to unsigned one and as result
this condition never triggers).

So to resolve it futex_abort_and_wake() is added and
should be used explicitly where appropriate instead
if signess hack.

Reported-by: Andrew Vagin <avagin at parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
---

Andrew, does it looks good for you?

 cr-restore.c   |    2 +-
 include/lock.h |   13 ++++++++++++-
 restorer.c     |    2 +-
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/cr-restore.c b/cr-restore.c
index 4f38c7f..f5fb91c 100644
--- a/cr-restore.c
+++ b/cr-restore.c
@@ -1132,7 +1132,7 @@ static void sigchld_handler(int signal, siginfo_t *siginfo, void *data)
 		pr_err("%d killed by signal %d\n",
 			siginfo->si_pid, siginfo->si_status);
 
-	futex_set_and_wake(&task_entries->nr_in_progress, -1);
+	futex_abort_and_wake(&task_entries->nr_in_progress);
 }
 
 static int restore_task_with_children(void *_arg)
diff --git a/include/lock.h b/include/lock.h
index 6f77bfd..be9ffdf 100644
--- a/include/lock.h
+++ b/include/lock.h
@@ -15,6 +15,9 @@ typedef struct {
 	u32	raw;
 } futex_t;
 
+#define FUTEX_ABORT_FLAG	(0x80000000)
+#define FUTEX_ABORT_RAW		(-1U)
+
 /* Get current futex @f value */
 static inline u32 futex_get(futex_t *f)
 {
@@ -37,7 +40,8 @@ static inline void futex_set(futex_t *f, u32 v)
 								\
 		while (1) {					\
 			tmp = (__f)->raw;			\
-			if (tmp __cond (__v))			\
+			if ((tmp & FUTEX_ABORT_FLAG) ||		\
+			    (tmp __cond (__v)))			\
 				break;				\
 			ret = sys_futex(&(__f)->raw, FUTEX_WAIT,\
 					tmp, NULL, NULL, 0);	\
@@ -52,6 +56,13 @@ static inline void futex_set_and_wake(futex_t *f, u32 v)
 	BUG_ON(sys_futex(&f->raw, FUTEX_WAKE, INT_MAX, NULL, NULL, 0) < 0);
 }
 
+/* Mark futex @f as wait abort needed and wake up all waiters */
+static inline void futex_abort_and_wake(futex_t *f)
+{
+	BUILD_BUG_ON(!(FUTEX_ABORT_RAW & FUTEX_ABORT_FLAG));
+	futex_set_and_wake(f, FUTEX_ABORT_RAW);
+}
+
 /* Decrement futex @f value and wake up all waiters */
 static inline void futex_dec_and_wake(futex_t *f)
 {
diff --git a/restorer.c b/restorer.c
index 18e5b6c..97798e9 100644
--- a/restorer.c
+++ b/restorer.c
@@ -46,7 +46,7 @@ static void sigchld_handler(int signal, siginfo_t *siginfo, void *data)
 		write_string(" killed by signal ");
 	write_num_n(siginfo->si_status);
 
-	futex_set_and_wake(&task_entries->nr_in_progress, -1);
+	futex_abort_and_wake(&task_entries->nr_in_progress);
 	/* sa_restorer may be unmaped, so we can't go back to userspace*/
 	sys_kill(sys_getpid(), SIGSTOP);
 	sys_exit(1);
-- 
1.7.7.6