6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Sergey Senozhatsky senozhatsky@chromium.org
commit f85219096648b251a81e9fe24a1974590cfc417d upstream.
Patch series "zram: IDLE flag handling fixes", v2.
zram can wrongly preserve ZRAM_IDLE flag on its entries which can result in premature post-processing (writeback and recompression) of such entries.
This patch (of 2)
Recompression should clear ZRAM_IDLE flag on the entries it has accessed, because otherwise some entries, specifically those for which recompression has failed, become immediate candidate entries for another post-processing (e.g. writeback).
Consider the following case: - recompression marks entries IDLE every 4 hours and attempts to recompress them - some entries are incompressible, so we keep them intact and hence preserve IDLE flag - writeback marks entries IDLE every 8 hours and writebacks IDLE entries, however we have IDLE entries left from recompression, so writeback prematurely writebacks those entries.
The bug was reported by Shin Kawamura.
Link: https://lkml.kernel.org/r/20241028153629.1479791-1-senozhatsky@chromium.org Link: https://lkml.kernel.org/r/20241028153629.1479791-2-senozhatsky@chromium.org Fixes: 84b33bf78889 ("zram: introduce recompress sysfs knob") Signed-off-by: Sergey Senozhatsky senozhatsky@chromium.org Reported-by: Shin Kawamura kawasin@google.com Acked-by: Brian Geffon bgeffon@google.com Cc: Minchan Kim minchan@kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/block/zram/zram_drv.c | 7 +++++++ 1 file changed, 7 insertions(+)
--- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1692,6 +1692,13 @@ static int zram_recompress(struct zram * if (ret) return ret;
+ /* + * We touched this entry so mark it as non-IDLE. This makes sure that + * we don't preserve IDLE flag and don't incorrectly pick this entry + * for different post-processing type (e.g. writeback). + */ + zram_clear_flag(zram, index, ZRAM_IDLE); + class_index_old = zs_lookup_class_index(zram->mem_pool, comp_len_old); /* * Iterate the secondary comp algorithms list (in order of priority)