[KJ] audit return code handling for kernel_thread [2/11]

[nhorman]

Audit/Cleanup of kernel_thread calls, specifically checking of return codes.
    Problems seemed to fall into 3 main categories:
    
    1) callers of kernel_thread were inconsistent about meaning of a zero return
    code.  Some callers considered a zero return code to mean success, others took
    it to mean failure.  a zero return code, while not actually possible in the
    current implementation, should be considered a success (pid 0 is/should be
    valid). fixed all callers to treat zero return as success
    
    2) caller of kernel_thread saved return code of kernel_thread for later use
    without ever checking its value.  Callers who did this tended to assume a
    non-zero return was success, and would often wait for a completion queue to be
    woken up, implying that an error (negative return code) from kernel_thread could
    lead to deadlock.  Repaired by checking return code at call time, and setting
    saved return code to zero in the event of an error.
    
    3) callers of kernel_thread never bothered to check the return code at all.
    This can lead to seemingly unrelated errors later in execution.  Fixed by
    checking return code at call time and printing a warning message on failure.

Regards
Neil
    
Signed-off-by: Neil Horman <nhorman@xxxxxxxxxxxxx>


 arch/s390/mm/cmm.c           |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/arch/s390/mm/cmm.c
+++ b/arch/s390/mm/cmm.c
@@ -161,7 +161,10 @@ cmm_thread(void *dummy)
 static void
 cmm_start_thread(void)
 {
-	kernel_thread(cmm_thread, NULL, 0);
+	if (kernel_thread(cmm_thread, NULL, 0) < 0) {
+		printk(KERN_WARNING "Could not start cmm thread\n");
+		clear_bit(0,&cmm_thread_active);
+	}
 }
 
 static void
-
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