zram: drop pp_in_progress

pp_in_progress makes sure that only one post-processing (writeback or
recomrpession) is active at any given time.  Functionality wise it,
basically, shadows zram init_lock, when init_lock is acquired in writer
mode.

Switch recompress_store() and writeback_store() to take zram init_lock in
writer mode, like all store() sysfs handlers should do, so that we can
drop pp_in_progress.  Recompression and writeback can be somewhat slow, so
holding init_lock in writer mode can block zram attrs reads, but in
reality the only zram attrs reads that take place are mm_stat reads, and
usually it's the same process that reads mm_stat and does recompression or
writeback.

Link: https://lkml.kernel.org/r/20251216071342.687993-1-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 7dcfc71d2cac45a102414324819b09ebc950db1e..ed717b65f0a9f53d71a3232e66c67891689f2814 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -902,7 +902,7 @@ release_wb_ctl:
 
 static void zram_account_writeback_rollback(struct zram *zram)
 {
-       lockdep_assert_held_read(&zram->init_lock);
+       lockdep_assert_held_write(&zram->init_lock);
 
        if (zram->wb_limit_enable)
                zram->bd_wb_limit +=  1UL << (PAGE_SHIFT - 12);
@@ -910,7 +910,7 @@ static void zram_account_writeback_rollback(struct zram *zram)
 
 static void zram_account_writeback_submit(struct zram *zram)
 {
-       lockdep_assert_held_read(&zram->init_lock);
+       lockdep_assert_held_write(&zram->init_lock);
 
        if (zram->wb_limit_enable && zram->bd_wb_limit > 0)
                zram->bd_wb_limit -=  1UL << (PAGE_SHIFT - 12);
@@ -1264,24 +1264,16 @@ static ssize_t writeback_store(struct device *dev,
        ssize_t ret = len;
        int err, mode = 0;
 
-       guard(rwsem_read)(&zram->init_lock);
+       guard(rwsem_write)(&zram->init_lock);
        if (!init_done(zram))
                return -EINVAL;
 
-       /* Do not permit concurrent post-processing actions. */
-       if (atomic_xchg(&zram->pp_in_progress, 1))
-               return -EAGAIN;
-
-       if (!zram->backing_dev) {
-               ret = -ENODEV;
-               goto out;
-       }
+       if (!zram->backing_dev)
+               return -ENODEV;
 
        pp_ctl = init_pp_ctl();
-       if (!pp_ctl) {
-               ret = -ENOMEM;
-               goto out;
-       }
+       if (!pp_ctl)
+               return -ENOMEM;
 
        wb_ctl = init_wb_ctl(zram);
        if (!wb_ctl) {
@@ -1358,7 +1350,6 @@ static ssize_t writeback_store(struct device *dev,
 out:
        release_pp_ctl(zram, pp_ctl);
        release_wb_ctl(wb_ctl);
-       atomic_set(&zram->pp_in_progress, 0);
 
        return ret;
 }
@@ -2619,14 +2610,10 @@ static ssize_t recompress_store(struct device *dev,
        if (threshold >= huge_class_size)
                return -EINVAL;
 
-       guard(rwsem_read)(&zram->init_lock);
+       guard(rwsem_write)(&zram->init_lock);
        if (!init_done(zram))
                return -EINVAL;
 
-       /* Do not permit concurrent post-processing actions. */
-       if (atomic_xchg(&zram->pp_in_progress, 1))
-               return -EAGAIN;
-
        if (algo) {
                bool found = false;
 
@@ -2697,7 +2684,6 @@ out:
        if (page)
                __free_page(page);
        release_pp_ctl(zram, ctl);
-       atomic_set(&zram->pp_in_progress, 0);
        return ret;
 }
 #endif
@@ -2888,7 +2874,6 @@ 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);
@@ -3124,7 +3109,6 @@ 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);
        zram_comp_params_reset(zram);
        comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);
 

diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 48d6861c664701ff59a78b46169a672aa06679ed..469a3dab44ad24bd9ce64fc0dd7a70a97dded607 100644 (file)
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -143,6 +143,5 @@ struct zram {
 #ifdef CONFIG_ZRAM_MEMORY_TRACKING
        struct dentry *debugfs_dir;
 #endif
-       atomic_t pp_in_progress;
 };
 #endif