From 4f6923fbb352d126659cabe34806cff75c7b5ea0 Mon Sep 17 00:00:00 2001
From: Howard McLauchlan <hmclauchlan@fb.com>
Date: Thu, 5 Apr 2018 16:23:57 -0700
Subject: mm: make should_failslab always available for fault injection

should_failslab() is a convenient function to hook into for directed
error injection into kmalloc().  However, it is only available if a
config flag is set.

The following BCC script, for example, fails kmalloc() calls after a
btrfs umount:

    from bcc import BPF

    prog = r"""
    BPF_HASH(flag);

    #include <linux/mm.h>

    int kprobe__btrfs_close_devices(void *ctx) {
            u64 key = 1;
            flag.update(&key, &key);
            return 0;
    }

    int kprobe__should_failslab(struct pt_regs *ctx) {
            u64 key = 1;
            u64 *res;
            res = flag.lookup(&key);
            if (res != 0) {
                bpf_override_return(ctx, -ENOMEM);
            }
            return 0;
    }
    """
    b = BPF(text=prog)

    while 1:
        b.kprobe_poll()

This patch refactors the should_failslab implementation so that the
function is always available for error injection, independent of flags.

This change would be similar in nature to commit f5490d3ec921 ("block:
Add should_fail_bio() for bpf error injection").

Link: http://lkml.kernel.org/r/20180222020320.6944-1-hmclauchlan@fb.com
Signed-off-by: Howard McLauchlan <hmclauchlan@fb.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Johannes Weiner <jweiner@fb.com>
Cc: Alexei Starovoitov <ast@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/failslab.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'mm/failslab.c')

diff --git a/mm/failslab.c b/mm/failslab.c
index 8087d976a809..1f2f248e3601 100644
--- a/mm/failslab.c
+++ b/mm/failslab.c
@@ -14,7 +14,7 @@ static struct {
 	.cache_filter = false,
 };
 
-bool should_failslab(struct kmem_cache *s, gfp_t gfpflags)
+bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
 {
 	/* No fault-injection for bootstrap cache */
 	if (unlikely(s == kmem_cache))
-- 
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