staging: android: logger: Correct write offset reset on error

In the situation that a writer fails to copy data from userspace it will reset
the write offset to the value it had before it went to sleep. This discarding
any messages written while aquiring the mutex.

Therefore the reset offset needs to be retrieved after acquiring the mutex.

Cc: Android Kernel Team <kernel-team@android.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/logger.c

@@ -469,7 +469,7 @@ static ssize_t logger_aio_write(struct kiocb *iocb, const struct iovec *iov,
 			 unsigned long nr_segs, loff_t ppos)
 {
 	struct logger_log *log = file_get_log(iocb->ki_filp);
-	size_t orig = log->w_off;
+	size_t orig;
 	struct logger_entry header;
 	struct timespec now;
 	ssize_t ret = 0;
@@ -490,6 +490,8 @@ static ssize_t logger_aio_write(struct kiocb *iocb, const struct iovec *iov,
 
 	mutex_lock(&log->mutex);
 
+	orig = log->w_off;
+
 	/*
 	 * Fix up any readers, pulling them forward to the first readable
 	 * entry after (what will be) the new write offset. We do this now