ipc/msg.c: use freezable blocking call

Avoid waking up every thread sleeping in a msgrcv call during suspend and
resume by calling a freezable blocking call.  Previous patches modified
the freezer to avoid sending wakeups to threads that are blocked in
freezable blocking calls.

Ref: https://lkml.org/lkml/2013/5/1/424

Backtrace: 
[<c03e3924>] (__schedule+0x0/0x5d8) from [<c03e3f88>] (schedule+0x8c/0x90)
[<c03e3efc>] (schedule+0x0/0x90) from [<c01ef9f8>] (do_msgrcv+0x2e0/0x368)
[<c01ef718>] (do_msgrcv+0x0/0x368) from [<c01efaac>] (SyS_msgrcv+0x2c/0x38)
[<c01efa80>] (SyS_msgrcv+0x0/0x38) from [<c001a180>] (ret_fast_syscall+0x0/0x48)
tPlay0Cb2       R running      0   297    204 0x00000001

This call was selected to be converted to a freezable call because it
doesn't hold any locks or release any resources when interrupted that
might be needed by another freezing task or a kernel driver during
suspend, and is a common site where idle userspace tasks are blocked.

Signed-off-by: Yogesh Gaur <[email protected]>
Signed-off-by: Manjeet Pawar <[email protected]>
Signed-off-by: Maninder Singh <[email protected]>
Reviewed-by : Ajeet Yadav <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Yogesh Gaur

ipc/msg.c

@@ -37,6 +37,7 @@
 #include <linux/rwsem.h>
 #include <linux/nsproxy.h>
 #include <linux/ipc_namespace.h>
+#include <linux/freezer.h>
 
 #include <asm/current.h>
 #include <linux/uaccess.h>
@@ -917,7 +918,7 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, int msgfl
 
 		ipc_unlock_object(&msq->q_perm);
 		rcu_read_unlock();
-		schedule();
+		freezable_schedule();
 
 		/* Lockless receive, part 1:
 		 * Disable preemption.  We don't hold a reference to the queue