On 2021/4/8 22:55, riteshh wrote: > On 21/04/08 09:08AM, Miaohe Lin wrote: >> Hi all, >> When I was investigating the swap code, I found some possible race >> windows. This series aims to fix all these races. But using current >> get/put_swap_device() to guard against concurrent swapoff for >> swap_readpage() looks terrible because swap_readpage() may take really >> long time. And to reduce the performance overhead on the hot-path as >> much as possible, it appears we can use the percpu_ref to close this >> race window(as suggested by Huang, Ying). The patch 1 adds percpu_ref >> support for swap and the rest of the patches use this to close various >> race windows. More details can be found in the respective changelogs. >> Thanks! >> >> Miaohe Lin (5): >> mm/swapfile: add percpu_ref support for swap >> swap: fix do_swap_page() race with swapoff >> mm/swap_state: fix get_shadow_from_swap_cache() race with swapoff >> mm/swap_state: fix potential faulted in race in swap_ra_info() >> mm/swap_state: fix swap_cluster_readahead() race with swapoff > Many thanks for quick respond. > Somehow I see Patch-1 and Patch-2 are missing on linux-mm[1]. I have no idea why Patch-1 and Patch-2 are missing. But they could be found at: https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg2542188.html > Also I wanted to ask if you have a way to trigger this in a more controlled > environment (consistently)? > This is *theoretical* issue. The race window is very small but not impossible. Please see the discussion: https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg2530094.html > [1]: https://patchwork.kernel.org/project/linux-mm/cover/20210408130820.48233-1-linmiaohe@xxxxxxxxxx/ > Thanks again. > -ritesh > >> >> include/linux/swap.h | 4 +++- >> mm/memory.c | 10 +++++++++ >> mm/swap_state.c | 33 +++++++++++++++++++++-------- >> mm/swapfile.c | 50 +++++++++++++++++++++++++++----------------- >> 4 files changed, 68 insertions(+), 29 deletions(-) >> >> -- >> 2.19.1 >> >> > . >
