mtd: mtdoops: panic caused mtdoops to call mtdoops_erase function immediately

The panic function disables the local interrupts, preemption, and all
other processors. When the invoked mtdoops needs to erase a used page,
calling schedule_work() to do it will not work. Instead, just call
mtdoops_erase function immediately.

Tested:
~# echo c > /proc/sysrq-trigger
[  171.654759] sysrq: Trigger a crash
[  171.658325] Kernel panic - not syncing: sysrq triggered crash
......
[  172.406423] mtdoops: not ready 34, 35 (erase immediately)
[  172.432285] mtdoops: ready 34, 35
[  172.435633] Rebooting in 10 seconds..
Signed-off-by: Ray Zhang <sgzhang@google.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20221010045549.2221965-4-sgzhang@google.com

drivers/mtd/mtdoops.c

@@ -170,7 +170,7 @@ static void mtdoops_workfunc_erase(struct work_struct *work)
 	mtdoops_erase(cxt);
 }
 
-static void mtdoops_inc_counter(struct mtdoops_context *cxt)
+static void mtdoops_inc_counter(struct mtdoops_context *cxt, int panic)
 {
 	cxt->nextpage++;
 	if (cxt->nextpage >= cxt->oops_pages)
@@ -180,12 +180,20 @@ static void mtdoops_inc_counter(struct mtdoops_context *cxt)
 		cxt->nextcount = 0;
 
 	if (page_is_used(cxt, cxt->nextpage)) {
-		schedule_work(&cxt->work_erase);
-		return;
+		pr_debug("not ready %d, %d (erase %s)\n",
+			 cxt->nextpage, cxt->nextcount,
+			 panic ? "immediately" : "scheduled");
+		if (panic) {
+			/* In case of panic, erase immediately */
+			mtdoops_erase(cxt);
+		} else {
+			/* Otherwise, schedule work to erase it "nicely" */
+			schedule_work(&cxt->work_erase);
+		}
+	} else {
+		pr_debug("ready %d, %d (no erase)\n",
+			 cxt->nextpage, cxt->nextcount);
 	}
-
-	pr_debug("ready %d, %d (no erase)\n",
-		 cxt->nextpage, cxt->nextcount);
 }
 
 static void mtdoops_write(struct mtdoops_context *cxt, int panic)
@@ -221,7 +229,7 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 	mark_page_used(cxt, cxt->nextpage);
 	memset(cxt->oops_buf, 0xff, record_size);
 
-	mtdoops_inc_counter(cxt);
+	mtdoops_inc_counter(cxt, panic);
 out:
 	clear_bit(0, &cxt->oops_buf_busy);
 }
@@ -286,7 +294,7 @@ static void find_next_position(struct mtdoops_context *cxt)
 		cxt->nextcount = maxcount;
 	}
 
-	mtdoops_inc_counter(cxt);
+	mtdoops_inc_counter(cxt, 0);
 }
 
 static void mtdoops_do_dump(struct kmsg_dumper *dumper,