mm: kmemleak: use the memory pool for early allocations

Currently kmemleak uses a static early_log buffer to trace all memory
allocation/freeing before the slab allocator is initialised.  Such early
log is replayed during kmemleak_init() to properly initialise the kmemleak
metadata for objects allocated up that point.  With a memory pool that
does not rely on the slab allocator, it is possible to skip this early log
entirely.

In order to remove the early logging, consider kmemleak_enabled == 1 by
default while the kmem_cache availability is checked directly on the
object_cache and scan_area_cache variables.  The RCU callback is only
invoked after object_cache has been initialised as we wouldn't have any
concurrent list traversal before this.

In order to reduce the number of callbacks before kmemleak is fully
initialised, move the kmemleak_init() call to mm_init().

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: remove WARN_ON(), per Catalin]
Link: http://lkml.kernel.org/r/20190812160642.52134-4-catalin.marinas@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 3c88e54da86c..c6975cded461 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -576,17 +576,18 @@ config DEBUG_KMEMLEAK
           In order to access the kmemleak file, debugfs needs to be
           mounted (usually at /sys/kernel/debug).
 
-config DEBUG_KMEMLEAK_EARLY_LOG_SIZE
-        int "Maximum kmemleak early log entries"
+config DEBUG_KMEMLEAK_MEM_POOL_SIZE
+        int "Kmemleak memory pool size"
         depends on DEBUG_KMEMLEAK
         range 200 40000
         default 16000
         help
           Kmemleak must track all the memory allocations to avoid
           reporting false positives. Since memory may be allocated or
-          freed before kmemleak is initialised, an early log buffer is
-          used to store these actions. If kmemleak reports "early log
-          buffer exceeded", please increase this value.
+          freed before kmemleak is fully initialised, use a static pool
+          of metadata objects to track such callbacks. After kmemleak is
+          fully initialised, this memory pool acts as an emergency one
+          if slab allocations fail.
 
 config DEBUG_KMEMLEAK_TEST
         tristate "Simple test for the kernel memory leak detector"