6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> [ Upstream commit 58652f2b6d21f2874c9f060165ec7e03e8b1fc71 ] Both recompress and writeback soon will unlock slots during processing, which makes things too complex wrt possible race-conditions. We still want to clear PP_SLOT in slot_free, because this is how we figure out that slot that was selected for post-processing has been released under us and when we start post-processing we check if slot still has PP_SLOT set. At the same time, theoretically, we can have something like this: CPU0 CPU1 recompress scan slots set PP_SLOT unlock slot slot_free clear PP_SLOT allocate PP_SLOT writeback scan slots set PP_SLOT unlock slot select PP-slot test PP_SLOT So recompress will not detect that slot has been re-used and re-selected for concurrent writeback post-processing. Make sure that we only permit on post-processing operation at a time. So now recompress and writeback post-processing don't race against each other, we only need to handle slot re-use (slot_free and write), which is handled individually by each pp operation. Having recompress and writeback competing for the same slots is not exactly good anyway (can't imagine anyone doing that). Link: https://lkml.kernel.org/r/20240917021020.883356-3-senozhatsky@xxxxxxxxxxxx Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Stable-dep-of: f364cdeb3893 ("zram: fix NULL pointer in comp_algorithm_show()") Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- Documentation/admin-guide/blockdev/zram.rst | 2 ++ drivers/block/zram/zram_drv.c | 16 ++++++++++++++++ drivers/block/zram/zram_drv.h | 1 + 3 files changed, 19 insertions(+) diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst index 678d70d6e1c3a..714a5171bfc0b 100644 --- a/Documentation/admin-guide/blockdev/zram.rst +++ b/Documentation/admin-guide/blockdev/zram.rst @@ -47,6 +47,8 @@ The list of possible return codes: -ENOMEM zram was not able to allocate enough memory to fulfil your needs. -EINVAL invalid input has been provided. +-EAGAIN re-try operation later (e.g. when attempting to run recompress + and writeback simultaneously). ======== ============================================================= If you use 'echo', the returned value is set by the 'echo' utility, diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index ad9c9bc3ccfc5..b742dc246b0c1 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -626,6 +626,12 @@ static ssize_t writeback_store(struct device *dev, goto release_init_lock; } + /* Do not permit concurrent post-processing actions. */ + if (atomic_xchg(&zram->pp_in_progress, 1)) { + up_read(&zram->init_lock); + return -EAGAIN; + } + if (!zram->backing_dev) { ret = -ENODEV; goto release_init_lock; @@ -752,6 +758,7 @@ static ssize_t writeback_store(struct device *dev, free_block_bdev(zram, blk_idx); __free_page(page); release_init_lock: + atomic_set(&zram->pp_in_progress, 0); up_read(&zram->init_lock); return ret; @@ -1881,6 +1888,12 @@ static ssize_t recompress_store(struct device *dev, goto release_init_lock; } + /* Do not permit concurrent post-processing actions. */ + if (atomic_xchg(&zram->pp_in_progress, 1)) { + up_read(&zram->init_lock); + return -EAGAIN; + } + if (algo) { bool found = false; @@ -1948,6 +1961,7 @@ static ssize_t recompress_store(struct device *dev, __free_page(page); release_init_lock: + atomic_set(&zram->pp_in_progress, 0); up_read(&zram->init_lock); return ret; } @@ -2144,6 +2158,7 @@ static void zram_reset_device(struct zram *zram) zram->disksize = 0; zram_destroy_comps(zram); memset(&zram->stats, 0, sizeof(zram->stats)); + atomic_set(&zram->pp_in_progress, 0); reset_bdev(zram); comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor); @@ -2381,6 +2396,7 @@ static int zram_add(void) zram->disk->fops = &zram_devops; zram->disk->private_data = zram; snprintf(zram->disk->disk_name, 16, "zram%d", device_id); + atomic_set(&zram->pp_in_progress, 0); /* Actual capacity set using sysfs (/sys/block/zram<id>/disksize */ set_capacity(zram->disk, 0); diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h index cfc8c059db636..8acf9d2ee42b8 100644 --- a/drivers/block/zram/zram_drv.h +++ b/drivers/block/zram/zram_drv.h @@ -139,5 +139,6 @@ struct zram { #ifdef CONFIG_ZRAM_MEMORY_TRACKING struct dentry *debugfs_dir; #endif + atomic_t pp_in_progress; }; #endif -- 2.43.0
