bcachefs: thread_with_file: fix various printf problems

Experimentally fix some problems with stdio_redirect_vprintf by creating
a MOO variant with which we can experiment.  We can't do a GFP_KERNEL
allocation while holding the spinlock, and I don't like how the printf
function can silently truncate the output if memory allocation fails.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/thread_with_file.c

@@ -366,48 +366,65 @@ int bch2_stdio_redirect_readline(struct stdio_redirect *stdio, char *ubuf, size_
 }
 
 __printf(3, 0)
-static void bch2_darray_vprintf(darray_char *out, gfp_t gfp, const char *fmt, va_list args)
+static ssize_t bch2_darray_vprintf(darray_char *out, gfp_t gfp, const char *fmt, va_list args)
 {
-	size_t len;
+	ssize_t ret;
 
 	do {
 		va_list args2;
-		va_copy(args2, args);
+		size_t len;
 
+		va_copy(args2, args);
 		len = vsnprintf(out->data + out->nr, darray_room(*out), fmt, args2);
-	} while (len + 1 > darray_room(*out) && !darray_make_room_gfp(out, len + 1, gfp));
+		if (len + 1 <= darray_room(*out)) {
+			out->nr += len;
+			return len;
+		}
 
-	out->nr += min(len, darray_room(*out));
+		ret = darray_make_room_gfp(out, len + 1, gfp);
+	} while (ret == 0);
+
+	return ret;
 }
 
-void bch2_stdio_redirect_vprintf(struct stdio_redirect *stdio, bool nonblocking,
-				 const char *fmt, va_list args)
+ssize_t bch2_stdio_redirect_vprintf(struct stdio_redirect *stdio, bool nonblocking,
+				    const char *fmt, va_list args)
 {
 	struct stdio_buf *buf = &stdio->output;
 	unsigned long flags;
+	ssize_t ret;
 
-	if (!nonblocking)
-		wait_event(buf->wait, stdio_redirect_has_output_space(stdio));
-	else if (!stdio_redirect_has_output_space(stdio))
-		return;
-	if (stdio->done)
-		return;
-
+again:
 	spin_lock_irqsave(&buf->lock, flags);
-	bch2_darray_vprintf(&buf->buf, nonblocking ? GFP_NOWAIT : GFP_KERNEL, fmt, args);
+	ret = bch2_darray_vprintf(&buf->buf, GFP_NOWAIT, fmt, args);
 	spin_unlock_irqrestore(&buf->lock, flags);
 
+	if (ret < 0) {
+		if (nonblocking)
+			return -EAGAIN;
+
+		ret = wait_event_interruptible(buf->wait,
+				stdio_redirect_has_output_space(stdio));
+		if (ret)
+			return ret;
+		goto again;
+	}
+
 	wake_up(&buf->wait);
+	return ret;
 }
 
-void bch2_stdio_redirect_printf(struct stdio_redirect *stdio, bool nonblocking,
+ssize_t bch2_stdio_redirect_printf(struct stdio_redirect *stdio, bool nonblocking,
 				const char *fmt, ...)
 {
-
 	va_list args;
+	ssize_t ret;
+
 	va_start(args, fmt);
-	bch2_stdio_redirect_vprintf(stdio, nonblocking, fmt, args);
+	ret = bch2_stdio_redirect_vprintf(stdio, nonblocking, fmt, args);
 	va_end(args);
+
+	return ret;
 }
 
 #endif /* NO_BCACHEFS_FS */

fs/bcachefs/thread_with_file.h

@@ -65,7 +65,7 @@ int bch2_run_thread_with_stdout(struct thread_with_stdio *,
 int bch2_stdio_redirect_read(struct stdio_redirect *, char *, size_t);
 int bch2_stdio_redirect_readline(struct stdio_redirect *, char *, size_t);
 
-__printf(3, 0) void bch2_stdio_redirect_vprintf(struct stdio_redirect *, bool, const char *, va_list);
-__printf(3, 4) void bch2_stdio_redirect_printf(struct stdio_redirect *, bool, const char *, ...);
+__printf(3, 0) ssize_t bch2_stdio_redirect_vprintf(struct stdio_redirect *, bool, const char *, va_list);
+__printf(3, 4) ssize_t bch2_stdio_redirect_printf(struct stdio_redirect *, bool, const char *, ...);
 
 #endif /* _BCACHEFS_THREAD_WITH_FILE_H */