Adding Thomas. Thomas I've been looking into the following test failure:
https://lore.kernel.org/lkml/20210304083825.GB17830@xsang-OptiPlex-9020/
See below.
On Fri, Mar 12, 2021 at 02:27:55PM +0800, Oliver Sang wrote:
> Hi Ira,
[snip]
> > > >
> > > > caused below changes (please refer to attached dmesg/kmsg for entire
> > > > log/backtrace):
> > >
> > > Is the fix for this been posted yet ?
> >
> > No. I've been unable to reproduce it yet.
>
> just FYI
> the issue does not always happen but the rate on 61b205f579 is not low,
> while we didn't observe it happen on parent commit.
>
> bb90d4bc7b6a536b 61b205f579911a11f0b576f7327
> ---------------- ---------------------------
> fail:runs %reproduction fail:runs
> | | |
> :38 16% 6:38 dmesg.EIP:__kmap_local_sched_in
> :38 16% 6:38 dmesg.EIP:__kmap_local_sched_out
> :38 16% 6:38
> dmesg.WARNING:at_mm/highmem.c:#__kmap_local_sched_in
> :38 16% 6:38
> dmesg.WARNING:at_mm/highmem.c:#__kmap_local_sched_out
>
> also please permit me to quote our internal analysis by Zhengjun (cced)
> (Thanks a lot, Zhengjun)
>
> "the commit has the potential to cause the issue.
> It replaces " kmap_atomic" to " kmap_local_page".
>
> Most of the two API is the same, except for " kmap_atomic" disable preemption
> and cannot sleep.
> I check the issue happened when there is a preemption, in FBC "
> kmap_local_page",
> the preemption is enabled, the issue may happen."
> "
I think I see the issue. I think this is an invalid configuration.
00:26:43 > grep DEBUG_KMAP config-5.11.0-rc7-00002-g61b205f57991
CONFIG_DEBUG_KMAP_LOCAL=y
CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP=y
00:26:48 > grep DEBUG_HIGHMEM config-5.11.0-rc7-00002-g61b205f57991
# CONFIG_DEBUG_HIGHMEM is not set
DEBUG_KMAP_LOCAL causes guard pages to be added to the kmap_ctrl array. But
DEBUG_HIGHMEM is used in __kmap_local_sched_out() to check the guard pages.
DEBUG_HIGHMEM is supposed to select DEBUG_KMAP_LOCAL... but apparently that
did not happen when this configuration was made.
I still have not hit this condition in my testing. Could you ensure that
DEBUG_HIGMEM is set and rerun the test to see if I am correct?
Thomas wouldn't the following enable checks make more sense? Or perhaps be
more consistent with the processing of kmap_ctrl?
Ira
diff --git a/mm/highmem.c b/mm/highmem.c
index 86f2b9495f9c..6ef8f5e05e7e 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -618,7 +618,7 @@ void __kmap_local_sched_out(void)
int idx;
/* With debug all even slots are unmapped and act as guard */
- if (IS_ENABLED(CONFIG_DEBUG_HIGHMEM) && !(i & 0x01)) {
+ if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL) && !(i & 0x01)) {
WARN_ON_ONCE(!pte_none(pteval));
continue;
}
@@ -654,7 +654,7 @@ void __kmap_local_sched_in(void)
int idx;
/* With debug all even slots are unmapped and act as guard */
- if (IS_ENABLED(CONFIG_DEBUG_HIGHMEM) && !(i & 0x01)) {
+ if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL) && !(i & 0x01)) {
WARN_ON_ONCE(!pte_none(pteval));
continue;
}
