6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> 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@xxxxxxxxxxxx Link: https://lkml.kernel.org/r/20241028153629.1479791-2-senozhatsky@xxxxxxxxxxxx Fixes: 84b33bf78889 ("zram: introduce recompress sysfs knob") Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> Reported-by: Shin Kawamura <kawasin@xxxxxxxxxx> Acked-by: Brian Geffon <bgeffon@xxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -1600,6 +1600,13 @@ 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)
