swap_cache_info.* could be accessed concurrently as noticed by
KCSAN,
BUG: KCSAN: data-race in lookup_swap_cache / lookup_swap_cache
write to 0xffffffff85517318 of 8 bytes by task 94138 on cpu 101:
lookup_swap_cache+0x12e/0x460
lookup_swap_cache at mm/swap_state.c:322
do_swap_page+0x112/0xeb0
__handle_mm_fault+0xc7a/0xd00
handle_mm_fault+0xfc/0x2f0
do_page_fault+0x263/0x6f9
page_fault+0x34/0x40
read to 0xffffffff85517318 of 8 bytes by task 91655 on cpu 100:
lookup_swap_cache+0x117/0x460
lookup_swap_cache at mm/swap_state.c:322
shmem_swapin_page+0xc7/0x9e0
shmem_getpage_gfp+0x2ca/0x16c0
shmem_fault+0xef/0x3c0
__do_fault+0x9e/0x220
do_fault+0x4a0/0x920
__handle_mm_fault+0xc69/0xd00
handle_mm_fault+0xfc/0x2f0
do_page_fault+0x263/0x6f9
page_fault+0x34/0x40
Reported by Kernel Concurrency Sanitizer on:
CPU: 100 PID: 91655 Comm: systemd-journal Tainted: G W O L 5.5.0-next-20200204+ #6
Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
write to 0xffffffff8d717308 of 8 bytes by task 11365 on cpu 87:
__delete_from_swap_cache+0x681/0x8b0
__delete_from_swap_cache at mm/swap_state.c:178
read to 0xffffffff8d717308 of 8 bytes by task 11275 on cpu 53:
__delete_from_swap_cache+0x66e/0x8b0
__delete_from_swap_cache at mm/swap_state.c:178
Both the read and write are done as lockless. Since swap_cache_info.*
are only used to print out counter information, even if any of them
missed a few incremental due to data races, it will be harmless, so just
mark it as an intentional data race using the data_race() macro.
While at it, fix a checkpatch.pl warning,
WARNING: Single statement macros should not use a do {} while (0) loop
Signed-off-by: Qian Cai <[email protected]>
---
mm/swap_state.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 8e7ce9a9bc5e..c0fcae432bdf 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -58,8 +58,8 @@ static bool enable_vma_readahead __read_mostly = true;
#define GET_SWAP_RA_VAL(vma) \
(atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
-#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
-#define ADD_CACHE_INFO(x, nr) do { swap_cache_info.x += (nr); } while (0)
+#define INC_CACHE_INFO(x) data_race(swap_cache_info.x++)
+#define ADD_CACHE_INFO(x, nr) data_race(swap_cache_info.x += (nr))
static struct {
unsigned long add_total;
--
2.21.0 (Apple Git-122.2)
> On Feb 9, 2020, at 9:00 PM, Andrew Morton <[email protected]> wrote:
>
> The data_race() macro appears to be stuck in Paul's linx-next tree.
> Can we expect this to be mainlined soon, or is there an issue?
I read Paul is trying to get this merged into the mainline no later than v5.7-rc1 or sooner.
lore.kernel.org/lkml/20200131211950.GX2935@paulmck-ThinkPad-P72/
On Sun, 9 Feb 2020 21:56:38 -0500 Qian Cai <[email protected]> wrote:
>
>
> > On Feb 9, 2020, at 9:00 PM, Andrew Morton <[email protected]> wrote:
> >
> > The data_race() macro appears to be stuck in Paul's linx-next tree.
> > Can we expect this to be mainlined soon, or is there an issue?
>
> I read Paul is trying to get this merged into the mainline no later than v5.7-rc1 or sooner.
>
> lore.kernel.org/lkml/20200131211950.GX2935@paulmck-ThinkPad-P72/
OK, thanks.
c48981eeb0d5 clearly can't break anything as it simply adds a macro.
Ingo, can we please get that upstream soonish?