On Wed, 31 Aug 2016 10:44:41 +0900 Sergey Senozhatsky
<sergey.senozhatsky.w...@gmail.com> wrote:
> On (08/30/16 15:03), Andrew Morton wrote:
> > > __printk_nmi_flush() can be called from nmi_panic(), therefore it has to
> > > test whether it's executed in NMI context and thus must route the messages
> > > through deferred printk() or via direct printk().
> >
> > Why? What misbehaviour does the current code cause?
>
> the reasoning behind the `if in_nmi()' in print_nmi_seq_line()
>
> if (in_nmi())
> printk_deferred("%.*s", (end - start) + 1, buf);
> else
> printk("%.*s", (end - start) + 1, buf);
>
> was as follows (per Petr's commit message)
OK, thanks, I altered the changelog thusly and scheduled the patch for 4.8:
--- txt/printk-nmi-avoid-direct-printk-s-from-__printk_nmi_flush.txt
+++ txt/printk-nmi-avoid-direct-printk-s-from-__printk_nmi_flush.txt
@@ -3,8 +3,13 @@
__printk_nmi_flush() can be called from nmi_panic(), therefore it has to
test whether it's executed in NMI context and thus must route the messages
-through deferred printk() or via direct printk(). Except for two places
-where __printk_nmi_flush() does unconditional direct printk() calls:
+through deferred printk() or via direct printk(). This is to avoid
+potential deadlocks, as described in cf9b1106c81c45cde ("printk/nmi: flush
+NMI messages on the system panic").
+
+However there remain two places where __printk_nmi_flush() does
+unconditional direct printk() calls:
+
- pr_err("printk_nmi_flush: internal error ...")
- pr_cont("\n")
