powerpc: Honor O_NONBLOCK flag when reading RTAS log

rtas_log_read() doesn't check file flags for O_NONBLOCK and blocks
non-blocking readers of /proc/ppc64/rtas/error_log when there is
no data available. This fixes it.

Also rtas_log_read() returns now with ENODATA to prevent suspending of
process in wait_event_interruptible() when logging facility was
switched off and log is already empty.

Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 18 insertions, 8 deletions

diff --git a/arch/powerpc/platforms/pseries/rtasd.c b/arch/powerpc/platforms/pseries/rtasd.c
index c9ffd8c225f1..f4e55be2eea9 100644
--- a/arch/powerpc/platforms/pseries/rtasd.c
+++ b/arch/powerpc/platforms/pseries/rtasd.c
@@ -295,19 +295,29 @@ static ssize_t rtas_log_read(struct file * file, char __user * buf,
         if (!tmp)
                 return -ENOMEM;
 
-
         spin_lock_irqsave(&rtasd_log_lock, s);
         /* if it's 0, then we know we got the last one (the one in NVRAM) */
-        if (rtas_log_size == 0 && logging_enabled)
-                nvram_clear_error_log();
-        spin_unlock_irqrestore(&rtasd_log_lock, s);
+        while (rtas_log_size == 0) {
+                if (file->f_flags & O_NONBLOCK) {
+                        spin_unlock_irqrestore(&rtasd_log_lock, s);
+                        error = -EAGAIN;
+                        goto out;
+                }
 
+                if (!logging_enabled) {
+                        spin_unlock_irqrestore(&rtasd_log_lock, s);
+                        error = -ENODATA;
+                        goto out;
+                }
+                nvram_clear_error_log();
 
-        error = wait_event_interruptible(rtas_log_wait, rtas_log_size);
-        if (error)
-                goto out;
+                spin_unlock_irqrestore(&rtasd_log_lock, s);
+                error = wait_event_interruptible(rtas_log_wait, rtas_log_size);
+                if (error)
+                        goto out;
+                spin_lock_irqsave(&rtasd_log_lock, s);
+        }
 
-        spin_lock_irqsave(&rtasd_log_lock, s);
         offset = rtas_error_log_buffer_max * (rtas_log_start & LOG_NUMBER_MASK);
         memcpy(tmp, &rtas_log_buf[offset], count);