git: b79f2bc6c5c7 - stable/13 - vt: panic while changing vt font

[Toomas Soome]

The branch stable/13 has been updated by tsoome:

URL: https://cgit.FreeBSD.org/src/commit/?id=b79f2bc6c5c7431fa1f7c02937ec97a64653ade1

commit b79f2bc6c5c7431fa1f7c02937ec97a64653ade1
Author:     Toomas Soome <tsoome at FreeBSD.org>
AuthorDate: 2021-01-24 18:59:36 +0000
Commit:     Toomas Soome <tsoome at FreeBSD.org>
CommitDate: 2021-02-02 10:11:38 +0000

    vt: panic while changing vt font
    
    Set refcount for loader provided font to 1 to prevent this font
    from being released (so we can reset to default).
    
    As we get started with no memory allocator, we set up static font data
    for font passed by loader (if there is any). At this time, we also must
    set refcount 1, and refcount will get incremented in cnprobe() callback.
    
    At some point the memory allocator will be available, and we will set up
    properly allocated font data, but we should not disturb the refcount.
    
    PR: 252833
    PR: 253147
    
    (cherry picked and squashed 93ebd6307efeb95a29bc614edd0c67c2af850e98 and
    1912d2b15e6d6f4a1d8c3886b03ab30d2f21f3fd)
---
 sys/dev/vt/vt_core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sys/dev/vt/vt_core.c b/sys/dev/vt/vt_core.c
index 2352ed823424..05c383829f49 100644
--- a/sys/dev/vt/vt_core.c
+++ b/sys/dev/vt/vt_core.c
@@ -1487,6 +1487,8 @@ parse_font_info_static(struct font_info *fi)
 	vfp = &vt_font_loader;
 	vfp->vf_height = fi->fi_height;
 	vfp->vf_width = fi->fi_width;
+	/* This is default font, set refcount 1 to disable removal. */
+	vfp->vf_refcount = 1;
 	for (unsigned i = 0; i < VFNT_MAPS; i++) {
 		if (fi->fi_map_count[i] == 0)
 			continue;
@@ -1499,6 +1501,12 @@ parse_font_info_static(struct font_info *fi)
 	return (vfp);
 }
 
+/*
+ * Set up default font with allocated data structures.
+ * However, we can not set refcount here, because it is already set and
+ * incremented in vtterm_cnprobe() to avoid being released by font load from
+ * userland.
+ */
 static struct vt_font *
 parse_font_info(struct font_info *fi)
 {