llkd: Add __get_user_page stack symbol checking
Add ro.llk.stack to list a set of symbols that should rarely happen
but if persistent in multiple checks, indicates a live lock condition.
At ro.llk.stack.timeout_ms the process is sent a kill, if it remains,
then panic the kernel.
There is no ABA detection in the paths, the condition for the
stack symbol being present instantaneously must be its rarity of
being caught. If a livelock occurs in the path of the symbol, then
it is possible more than one path could be stuck in the state, but
the best candidate symbols are found underneath a lock resulting in
only one process being the culprit, and the best aim. There may be
processes that induce a look of persistence, if so the symbol is not
a candidate for checking.
The current candidate is __get_user_pages, after mm is locked,
should be a very short reference to look up a page, but can be
longer term if starved, or a condition causes a conflicting loop.
Test: compile
Bug: 33808187
Change-Id: I946e85641e59229b7491e929fcab5f1240794254
diff --git a/llkd/README.md b/llkd/README.md
index 1f69718..9a24682 100644
--- a/llkd/README.md
+++ b/llkd/README.md
@@ -127,7 +127,7 @@
default 2 minutes samples of threads for D or Z.
#### ro.llk.stack
-default *empty* or false, comma separated list of kernel symbols.
+default __get_user_pages, comma separated list of kernel symbols.
The string "*false*" is the equivalent to an *empty* list.
Look for kernel stack symbols that if ever persistently present can
indicate a subsystem is locked up.
diff --git a/llkd/include/llkd.h b/llkd/include/llkd.h
index d0188ec..915ee90 100644
--- a/llkd/include/llkd.h
+++ b/llkd/include/llkd.h
@@ -48,7 +48,7 @@
/* LLK_CHECK_MS_DEFAULT = actual timeout_ms / LLK_CHECKS_PER_TIMEOUT_DEFAULT */
#define LLK_CHECKS_PER_TIMEOUT_DEFAULT 5
#define LLK_CHECK_STACK_PROPERTY "ro.llk.stack"
-#define LLK_CHECK_STACK_DEFAULT ""
+#define LLK_CHECK_STACK_DEFAULT "__get_user_pages"
#define LLK_BLACKLIST_PROCESS_PROPERTY "ro.llk.blacklist.process"
#define LLK_BLACKLIST_PROCESS_DEFAULT \
"0,1,2,init,[kthreadd],[khungtaskd],lmkd,lmkd.llkd,llkd,watchdogd,[watchdogd],[watchdogd/0]"