[patch 028/163] mm, slub: extend slub_debug syntax for multiple blocks

Andrew Morton
2020-08-07T06:18:38Z

From: Vlastimil Babka <vbabka@suse.cz>
Subject: mm, slub: extend slub_debug syntax for multiple blocks

Patch series "slub_debug fixes and improvements".

The slub_debug kernel boot parameter can either apply a single set of
options to all caches or a list of caches. There is a use case where
debugging is applied for all caches and then disabled at runtime for
specific caches, for performance and memory consumption reasons [1]. As
runtime changes are dangerous, extend the boot parameter syntax so that
multiple blocks of either global or slab-specific options can be
specified, with blocks delimited by ';'. This will also support the use
case of [1] without runtime changes.

For details see the updated Documentation/vm/slub.rst

[1] https://lore.kernel.org/r/1383cd32-1ddc-4dac-b5f8-9c42282fa81c@codeaurora.org

[weiyongjun1@huawei.com: make parse_slub_debug_flags() static]
Link: http://lkml.kernel.org/r/20200702150522.4940-1-weiyongjun1@huawei.com
Link: http://lkml.kernel.org/r/20200610163135.17364-2-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: Jann Horn <jannh@google.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

Documentation/admin-guide/kernel-parameters.txt | 2
Documentation/vm/slub.rst | 18 +
mm/slub.c | 179 +++++++++-----
3 files changed, 146 insertions(+), 53 deletions(-)

--- a/Documentation/admin-guide/kernel-parameters.txt~mm-slub-extend-slub_debug-syntax-for-multiple-blocks
+++ a/Documentation/admin-guide/kernel-parameters.txt
@@ -4689,7 +4689,7 @@
fragmentation. Defaults to 1 for systems with
more than 32MB of RAM, 0 otherwise.

- slub_debug[=options[,slabs]] [MM, SLUB]
+ slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
Enabling slub_debug allows one to determine the
culprit if slab objects become corrupted. Enabling
slub_debug can create guard zones around objects and
--- a/Documentation/vm/slub.rst~mm-slub-extend-slub_debug-syntax-for-multiple-blocks
+++ a/Documentation/vm/slub.rst
@@ -41,6 +41,11 @@ slub_debug=<Debug-Options>,<slab name1>,
Enable options only for select slabs (no spaces
after a comma)

+Multiple blocks of options for all slabs or selected slabs can be given, with
+blocks of options delimited by ';'. The last of "all slabs" blocks is applied
+to all slabs except those that match one of the "select slabs" block. Options
+of the first "select slabs" blocks that matches the slab's name are applied.
+
Possible debug options are::

F Sanity checks on (enables SLAB_DEBUG_CONSISTENCY_CHECKS
@@ -83,6 +88,19 @@ switch off debugging for such caches by

slub_debug=O

+You can apply different options to different list of slab names, using blocks
+of options. This will enable red zoning for dentry and user tracking for
+kmalloc. All other slabs will not get any debugging enabled::
+
+ slub_debug=Z,dentry;U,kmalloc-*
+
+You can also enable options (e.g. sanity checks and poisoning) for all caches
+except some that are deemed too performance critical and don't need to be
+debugged by specifying global debug options followed by a list of slab names
+with "-" as options::
+
+ slub_debug=FZ;-,zs_handle,zspage
+
In case you forgot to enable debugging on the kernel command line: It is
possible to enable debugging manually when the kernel is up. Look at the
contents of::
--- a/mm/slub.c~mm-slub-extend-slub_debug-syntax-for-multiple-blocks
+++ a/mm/slub.c
@@ -499,7 +499,7 @@ static slab_flags_t slub_debug = DEBUG_D
static slab_flags_t slub_debug;
#endif

-static char *slub_debug_slabs;
+static char *slub_debug_string;
static int disable_higher_order_debug;

/*
@@ -1262,68 +1262,132 @@ out:
return ret;
}

-static int __init setup_slub_debug(char *str)
+/*
+ * Parse a block of slub_debug options. Blocks are delimited by ';'
+ *
+ * @str: start of block
+ * @flags: returns parsed flags, or DEBUG_DEFAULT_FLAGS if none specified
+ * @slabs: return start of list of slabs, or NULL when there's no list
+ * @init: assume this is initial parsing and not per-kmem-create parsing
+ *
+ * returns the start of next block if there's any, or NULL
+ */
+static char *
+parse_slub_debug_flags(char *str, slab_flags_t *flags, char **slabs, bool init)
{
- slub_debug = DEBUG_DEFAULT_FLAGS;
- if (*str++ != '=' || !*str)
- /*
- * No options specified. Switch on full debugging.
- */
- goto out;
+ bool higher_order_disable = false;

- if (*str == ',')
+ /* Skip any completely empty blocks */
+ while (*str && *str == ';')
+ str++;
+
+ if (*str == ',') {
/*
* No options but restriction on slabs. This means full
* debugging for slabs matching a pattern.
*/
+ *flags = DEBUG_DEFAULT_FLAGS;
goto check_slabs;
+ }
+ *flags = 0;

- slub_debug = 0;
- if (*str == '-')
- /*
- * Switch off all debugging measures.
- */
- goto out;
-
- /*
- * Determine which debug features should be switched on
- */
- for (; *str && *str != ','; str++) {
+ /* Determine which debug features should be switched on */
+ for (; *str && *str != ',' && *str != ';'; str++) {
switch (tolower(*str)) {
+ case '-':
+ *flags = 0;
+ break;
case 'f':
- slub_debug |= SLAB_CONSISTENCY_CHECKS;
+ *flags |= SLAB_CONSISTENCY_CHECKS;
break;
case 'z':
- slub_debug |= SLAB_RED_ZONE;
+ *flags |= SLAB_RED_ZONE;
break;
case 'p':
- slub_debug |= SLAB_POISON;
+ *flags |= SLAB_POISON;
break;
case 'u':
- slub_debug |= SLAB_STORE_USER;
+ *flags |= SLAB_STORE_USER;
break;
case 't':
- slub_debug |= SLAB_TRACE;
+ *flags |= SLAB_TRACE;
break;
case 'a':
- slub_debug |= SLAB_FAILSLAB;
+ *flags |= SLAB_FAILSLAB;
break;
case 'o':
/*
* Avoid enabling debugging on caches if its minimum
* order would increase as a result.
*/
- disable_higher_order_debug = 1;
+ higher_order_disable = true;
break;
default:
- pr_err("slub_debug option '%c' unknown. skipped\n",
- *str);
+ if (init)
+ pr_err("slub_debug option '%c' unknown. skipped\n", *str);
}
}
-
check_slabs:
if (*str == ',')
- slub_debug_slabs = str + 1;
+ *slabs = ++str;
+ else
+ *slabs = NULL;
+
+ /* Skip over the slab list */
+ while (*str && *str != ';')
+ str++;
+
+ /* Skip any completely empty blocks */
+ while (*str && *str == ';')
+ str++;
+
+ if (init && higher_order_disable)
+ disable_higher_order_debug = 1;
+
+ if (*str)
+ return str;
+ else
+ return NULL;
+}
+
+static int __init setup_slub_debug(char *str)
+{
+ slab_flags_t flags;
+ char *saved_str;
+ char *slab_list;
+ bool global_slub_debug_changed = false;
+ bool slab_list_specified = false;
+
+ slub_debug = DEBUG_DEFAULT_FLAGS;
+ if (*str++ != '=' || !*str)
+ /*
+ * No options specified. Switch on full debugging.
+ */
+ goto out;
+
+ saved_str = str;
+ while (str) {
+ str = parse_slub_debug_flags(str, &flags, &slab_list, true);
+
+ if (!slab_list) {
+ slub_debug = flags;
+ global_slub_debug_changed = true;
+ } else {
+ slab_list_specified = true;
+ }
+ }
+
+ /*
+ * For backwards compatibility, a single list of flags with list of
+ * slabs means debugging is only enabled for those slabs, so the global
+ * slub_debug should be 0. We can extended that to multiple lists as
+ * long as there is no option specifying flags without a slab list.
+ */
+ if (slab_list_specified) {
+ if (!global_slub_debug_changed)
+ slub_debug = 0;
+ slub_debug_string = saved_str;
+ }
out:
if ((static_branch_unlikely(&init_on_alloc) ||
static_branch_unlikely(&init_on_free)) &&
@@ -1352,36 +1416,47 @@ slab_flags_t kmem_cache_flags(unsigned i
{
char *iter;
size_t len;
+ char *next_block;
+ slab_flags_t block_flags;

/* If slub_debug = 0, it folds into the if conditional. */
- if (!slub_debug_slabs)
+ if (!slub_debug_string)
return flags | slub_debug;

len = strlen(name);
- iter = slub_debug_slabs;
- while (*iter) {
- char *end, *glob;
- size_t cmplen;
-
- end = strchrnul(iter, ',');
-
- glob = strnchr(iter, end - iter, '*');
- if (glob)
- cmplen = glob - iter;
- else
- cmplen = max_t(size_t, len, (end - iter));
+ next_block = slub_debug_string;
+ /* Go through all blocks of debug options, see if any matches our slab's name */
+ while (next_block) {
+ next_block = parse_slub_debug_flags(next_block, &block_flags, &iter, false);
+ if (!iter)
+ continue;
+ /* Found a block that has a slab list, search it */
+ while (*iter) {
+ char *end, *glob;
+ size_t cmplen;
+
+ end = strchrnul(iter, ',');
+ if (next_block && next_block < end)
+ end = next_block - 1;
+
+ glob = strnchr(iter, end - iter, '*');
+ if (glob)
+ cmplen = glob - iter;
+ else
+ cmplen = max_t(size_t, len, (end - iter));

- if (!strncmp(name, iter, cmplen)) {
- flags |= slub_debug;
- break;
- }
+ if (!strncmp(name, iter, cmplen)) {
+ flags |= block_flags;
+ return flags;
+ }

- if (!*end)
- break;
- iter = end + 1;
+ if (!*end || *end == ';')
+ break;
+ iter = end + 1;
+ }
}

- return flags;
+ return slub_debug;
}
#else /* !CONFIG_SLUB_DEBUG */
static inline void setup_object_debug(struct kmem_cache *s,
_