Re: [bug report] mm/zswap :memory corruption after zswap_load().

[Chengming Zhou <chengming.zhou@linux.dev>]

On 2024/3/21 12:34, Zhongkun He wrote:
> Hey folks,
> 
> Recently, I tested the zswap with memory reclaiming in the mainline
> (6.8) and found a memory corruption issue related to exclusive loads.

Is this fix included? 13ddaf26be32 ("mm/swap: fix race when skipping swapcache")
This fix avoids concurrent swapin using the same swap entry.

Thanks.

> 
> 
> root@**:/sys/fs/cgroup/zz# stress --vm 5 --vm-bytes 1g --vm-hang 3 --vm-keep
> stress: info: [31753] dispatching hogs: 0 cpu, 0 io, 5 vm, 0 hdd
> stress: FAIL: [31758] (522) memory corruption at: 0x7f347ed1a010
> stress: FAIL: [31753] (394) <-- worker 31758 returned error 1
> stress: WARN: [31753] (396) now reaping child worker processes
> stress: FAIL: [31753] (451) failed run completed in 14s
> 
> 
> 1. Test step(the frequency of memory reclaiming has been accelerated):
> -------------------------
> a. set up the zswap, zram and cgroup V2
> b. echo 0 > /sys/kernel/mm/lru_gen/enabled
>       (Increase the probability of problems occurring)
> c.  mkdir /sys/fs/cgroup/zz
>      echo $$  > /sys/fs/cgroup/zz/cgroup.procs
>      cd  /sys/fs/cgroup/zz/
>      stress --vm 5 --vm-bytes 1g --vm-hang 3 --vm-keep
> 
> e. in other shell:
>    while :;do for i in {1..5};do echo 20g >
> /sys/fs/cgroup/zz/memory.reclaim & done;sleep 1;done
> 
> 2. Root cause:
> --------------------------
> With a small probability, the page fault will occur twice with the
> original pte, even if a new pte has been successfully set.
> Unfortunately, zswap_entry has been released during the first page fault
> with exclusive loads, so zswap_load will fail, and there is no corresponding
> data in swap space, memory corruption occurs.
> 
> bpftrace -e'k:zswap_load {printf("%lld, %lld\n", ((struct page
> *)arg0)->private,nsecs)}'
> --include linux/mm_types.h  > a.txt
> 
> look up the same index:
> 
> index            nsecs
> 1318876, 8976040736819
> 1318876, 8976040746078
> 
> 4123110, 8976234682970
> 4123110, 8976234689736
> 
> 2268896, 8976660124792
> 2268896, 8976660130607
> 
> 4634105, 8976662117938
> 4634105, 8976662127596
> 
> 3. Solution
> 
> Should we free zswap_entry in batches so that zswap_entry will be
> valid when the next page fault occurs with the
> original pte? It would be great if there are other better solutions.
>