[PATCH] log: fixup log_head after relocating global data

[Thomas Weißschuh]

When `gd` is relocated during `spl_relocate_stack_gd()` the
doubly-linked circular list in the `log_head` member is broken.

The last element of the list should point back to the initial
`list_head`, but as the initial `list_head` is moved the pointer becomes
stale. As a result the loop in `log_dispatch` would never finish.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh at linutronix.de>
---
This patch is a simpler alternative to https://lore.kernel.org/u-boot/20240212-spl-logging-v1-1-051cde837559@linutronix.de/

This patch should also remove the special handling introduced in
commit e7595aa350ae ("x86: Allow logging to be used in SPL reliably").
---
 common/log.c     |  4 ++++
 common/spl/spl.c |  3 +++
 include/log.h    | 12 ++++++++++++
 3 files changed, 19 insertions(+)

diff --git a/common/log.c b/common/log.c
index b2de57fcb3b8..0ca2d1b4c8bc 100644
--- a/common/log.c
+++ b/common/log.c
@@ -428,6 +428,10 @@ int log_device_set_enable(struct log_driver *drv, bool enable)
 	return 0;
 }
 
+void log_fixup_for_gd_move(struct global_data *new_gd) {
+	new_gd->log_head.prev->next = &new_gd->log_head;
+}
+
 int log_init(void)
 {
 	struct log_driver *drv = ll_entry_start(struct log_driver, log_driver);
diff --git a/common/spl/spl.c b/common/spl/spl.c
index b65c439e7aa9..e06bc75d36b2 100644
--- a/common/spl/spl.c
+++ b/common/spl/spl.c
@@ -909,6 +909,9 @@ ulong spl_relocate_stack_gd(void)
 #if CONFIG_IS_ENABLED(DM)
 	dm_fixup_for_gd_move(new_gd);
 #endif
+#if CONFIG_IS_ENABLED(LOG)
+	log_fixup_for_gd_move(new_gd);
+#endif
 #if !defined(CONFIG_ARM) && !defined(CONFIG_RISCV)
 	gd = new_gd;
 #endif
diff --git a/include/log.h b/include/log.h
index 6e84f080ef3d..fc0d59844728 100644
--- a/include/log.h
+++ b/include/log.h
@@ -688,4 +688,16 @@ static inline int log_get_default_format(void)
 	       (IS_ENABLED(CONFIG_LOGF_FUNC) ? BIT(LOGF_FUNC) : 0);
 }
 
+struct global_data;
+/**
+ * log_fixup_for_gd_move() - Handle global_data moving to a new place
+ *
+ * @new_gd: Pointer to the new global data
+ *
+ * The log_head list is part of global_data. Due to the way lists work, moving
+ * the list will cause it to become invalid. This function fixes that up so
+ * that the log_head list will work correctly.
+ */
+void log_fixup_for_gd_move(struct global_data *new_gd);
+
 #endif

---
base-commit: 73b5b47dd5b546d0b9106bcca54c72815380e6d3
change-id: 20240213-spl-logging-2-43a81ae0f147

Best regards,
-- 
Thomas Weißschuh <thomas.weissschuh at linutronix.de>