Sometimes it is desirable to override SLUB's debug facilities
default behavior upon stumbling on a cache or object error
and just stop the execution in order to grab a coredump, at
the error-spotting time, instead of trying to fix the issue
and report in an attempt to keep the system rolling.
This patch introduces a new debug flag SLAB_PANIC_ON_ERROR,
along with its related SLUB-machinery, in order to extend
current slub_debug facilites and provide the aforementioned
behavior override.
Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx>
---
Documentation/vm/slub.rst | 2 ++
include/linux/slab.h | 2 ++
mm/slab.h | 3 ++-
mm/slub.c | 44 ++++++++++++++++++++++++++++++---------
4 files changed, 40 insertions(+), 11 deletions(-)
diff --git a/Documentation/vm/slub.rst b/Documentation/vm/slub.rst
index 933ada4368ff..51b18c28ec78 100644
--- a/Documentation/vm/slub.rst
+++ b/Documentation/vm/slub.rst
@@ -54,6 +54,8 @@ Possible debug options are::
caused higher minimum slab orders
- Switch all debugging off (useful if the kernel is
configured with CONFIG_SLUB_DEBUG_ON)
+ C Toggle panic on error (crash) to allow for post-mortem
+ analysis of a coredump taken at the error-spotting time
F.e. in order to boot just with sanity checks and red zoning one would specify::
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 6d454886bcaf..e3496ad7859f 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -25,6 +25,8 @@
*/
/* DEBUG: Perform (expensive) checks on alloc/free */
#define SLAB_CONSISTENCY_CHECKS ((slab_flags_t __force)0x00000100U)
+/* DEBUG: panic on error (forced crash) */
+#define SLAB_PANIC_ON_ERROR ((slab_flags_t __force)0x00000200U)
/* DEBUG: Red zone objs in a cache */
#define SLAB_RED_ZONE ((slab_flags_t __force)0x00000400U)
/* DEBUG: Poison objects */
diff --git a/mm/slab.h b/mm/slab.h
index 207c83ef6e06..27116f8683a1 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -198,7 +198,8 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
#define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER)
#elif defined(CONFIG_SLUB_DEBUG)
#define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
- SLAB_TRACE | SLAB_CONSISTENCY_CHECKS)
+ SLAB_TRACE | SLAB_CONSISTENCY_CHECKS | \
+ SLAB_PANIC_ON_ERROR)
#else
#define SLAB_DEBUG_FLAGS (0)
#endif
diff --git a/mm/slub.c b/mm/slub.c
index 9bf44955c4f1..8b4fc002b865 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -700,8 +700,6 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
/* Beginning of the filler is the free pointer */
print_section(KERN_ERR, "Padding ", p + off,
size_from_object(s) - off);
-
- dump_stack();
}
void object_err(struct kmem_cache *s, struct page *page,
@@ -709,6 +707,9 @@ void object_err(struct kmem_cache *s, struct page *page,
{
slab_bug(s, "%s", reason);
print_trailer(s, page, object);
+ if (unlikely(s->flags & SLAB_PANIC_ON_ERROR))
+ panic("BUG: %s: %s", s->name, reason);
+ dump_stack();
}
static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page,
@@ -722,6 +723,8 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page,
va_end(args);
slab_bug(s, "%s", buf);
print_page_info(page);
+ if (unlikely(s->flags & SLAB_PANIC_ON_ERROR))
+ panic("BUG: %s: %s", s->name, buf);
dump_stack();
}
@@ -771,7 +774,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page,
fault, end - 1, fault - addr,
fault[0], value);
print_trailer(s, page, object);
-
+ dump_stack();
restore_bytes(s, what, value, fault, end);
return 0;
}
@@ -1173,13 +1176,14 @@ static inline int free_consistency_checks(struct kmem_cache *s,
if (!PageSlab(page)) {
slab_err(s, page, "Attempt to free object(0x%p) outside of slab",
object);
- } else if (!page->slab_cache) {
- pr_err("SLUB <none>: no slab for object 0x%p.\n",
- object);
- dump_stack();
- } else
- object_err(s, page, object,
- "page slab pointer corrupt.");
+ } else {
+ char reason[80];
+
+ snprintf(reason, sizeof(reason),
+ "page slab pointer corruption: 0x%p (0x%p expected)",
+ page->slab_cache, s);
+ object_err(s, page, object, reason);
+ }
return 0;
}
return 1;
@@ -1291,6 +1295,9 @@ static int __init setup_slub_debug(char *str)
*/
disable_higher_order_debug = 1;
break;
+ case 'c':
+ slub_debug |= SLAB_PANIC_ON_ERROR;
+ break;
default:
pr_err("slub_debug option '%c' unknown. skipped\n",
*str);
@@ -5312,6 +5319,22 @@ static ssize_t free_calls_show(struct kmem_cache *s, char *buf)
return list_locations(s, buf, TRACK_FREE);
}
SLAB_ATTR_RO(free_calls);
+
+static ssize_t
+panic_on_error_show(struct kmem_cache *s, char *buf)
+{
+ return sprintf(buf, "%d\n", !!(s->flags & SLAB_PANIC_ON_ERROR));
+}
+
+static ssize_t
+panic_on_error_store(struct kmem_cache *s, const char *buf, size_t length)
+{
+ s->flags &= ~SLAB_PANIC_ON_ERROR;
+ if (buf[0] == '1')
+ s->flags |= SLAB_PANIC_ON_ERROR;
+ return length;
+}
+SLAB_ATTR(panic_on_error);
#endif /* CONFIG_SLUB_DEBUG */
#ifdef CONFIG_FAILSLAB
@@ -5486,6 +5509,7 @@ static struct attribute *slab_attrs[] = {
&validate_attr.attr,
&alloc_calls_attr.attr,
&free_calls_attr.attr,
+ &panic_on_error_attr.attr,
#endif
#ifdef CONFIG_ZONE_DMA
&cache_dma_attr.attr,
--
2.25.4
