From: Vlastimil Babka <vbabka@xxxxxxx>
Subject: mm, frontswap: make sure allocated frontswap map is assigned
Christian Borntraeger reports:
with commit 8ea1d2a1985a7ae096e ("mm, frontswap: convert frontswap_enabled
to static key") kmemleak complains about a memory leak in swapon
unreferenced object 0x3e09ba56000 (size 32112640):
comm "swapon", pid 7852, jiffies 4294968787 (age 1490.770s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<00000000003a2504>] __vmalloc_node_range+0x194/0x2d8
[<00000000003a2918>] vzalloc+0x58/0x68
[<00000000003b0af0>] SyS_swapon+0xd60/0x12f8
[<0000000000a3dc2e>] system_call+0xd6/0x270
[<ffffffffffffffff>] 0xffffffffffffffff
Turns out kmemleak is right. We now allocate the frontswap map depending on the
kernel config (and no longer on the enablement)
swapfile.c:
[...]
if (IS_ENABLED(CONFIG_FRONTSWAP))
frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long));
but later on this is passed along
--> enable_swap_info(p, prio, swap_map, cluster_info, frontswap_map);
and ignored if frontswap is disabled
--> frontswap_init(p->type, frontswap_map);
static inline void frontswap_init(unsigned type, unsigned long *map)
{
if (frontswap_enabled())
__frontswap_init(type, map);
}
Thing is, that frontswap map is never freed.
===
The leakage is relatively not that bad, because swapon is an infrequent
and privileged operation. However, if the first frontswap backend is
registered after a swap type has been already enabled, it will WARN_ON in
frontswap_register_ops() and frontswap will not be available for the swap
type.
Fix this by making sure the map is assigned by frontswap_init() as long as
CONFIG_FRONTSWAP is enabled.
Fixes: 8ea1d2a1985a ("mm, frontswap: convert frontswap_enabled to static key")
Link: http://lkml.kernel.org/r/20161026134220.2566-1-vbabka@xxxxxxx
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Reported-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/frontswap.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff -puN include/linux/frontswap.h~mm-frontswap-make-sure-allocated-frontswap-map-is-assigned include/linux/frontswap.h
--- a/include/linux/frontswap.h~mm-frontswap-make-sure-allocated-frontswap-map-is-assigned
+++ a/include/linux/frontswap.h
@@ -106,8 +106,9 @@ static inline void frontswap_invalidate_
static inline void frontswap_init(unsigned type, unsigned long *map)
{
- if (frontswap_enabled())
- __frontswap_init(type, map);
+#ifdef CONFIG_FRONTSWAP
+ __frontswap_init(type, map);
+#endif
}
#endif /* _LINUX_FRONTSWAP_H */
_
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