Admin could reset zram during I/O operation going on so we have
used zram->init_lock as read-side lock in I/O path to prevent
sudden zram meta freeing.
However, the init_lock is really troublesome.
We can't do call zram_meta_alloc under init_lock due to lockdep splat
because zram_rw_page is one of the function under reclaim path and
hold it as read_lock while other places in process context hold it
as write_lock. So, we have used allocation out of the lock to avoid
lockdep warn but it's not good for readability and fainally, I met
another lockdep splat between init_lock and cpu_hotpulug from
kmem_cache_destroy during wokring zsmalloc compaction. :(
Yes, the ideal is to remove horrible init_lock of zram in rw path.
This patch removes it in rw path and instead, put init_done bool
variable to check initialization done with smp_[wmb|rmb] and
srcu_[un]read_lock to prevent sudden zram meta freeing
during I/O operation.
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 85 +++++++++++++++++++++++++++++++------------
drivers/block/zram/zram_drv.h | 5 +++
2 files changed, 66 insertions(+), 24 deletions(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index a598ada817f0..b33add453027 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -32,6 +32,7 @@
#include <linux/string.h>
#include <linux/vmalloc.h>
#include <linux/err.h>
+#include <linux/srcu.h>
#include "zram_drv.h"
@@ -53,9 +54,31 @@ static ssize_t name##_show(struct device *d, \
} \
static DEVICE_ATTR_RO(name);
-static inline int init_done(struct zram *zram)
+static inline bool init_done(struct zram *zram)
{
- return zram->meta != NULL;
+ /*
+ * init_done can be used without holding zram->init_lock in
+ * read/write handler(ie, zram_make_request) but we should make sure
+ * that zram->init_done should set up after meta initialization is
+ * done. Look at setup_init_done.
+ */
+ bool ret = zram->init_done;
+
+ if (ret)
+ smp_rmb(); /* pair with setup_init_done */
+
+ return ret;
+}
+
+static inline void setup_init_done(struct zram *zram, bool flag)
+{
+ /*
+ * Store operation of struct zram fields should complete
+ * before zram->init_done set up because zram_bvec_rw
+ * doesn't hold an zram->init_lock.
+ */
+ smp_wmb();
+ zram->init_done = flag;
}
static inline struct zram *dev_to_zram(struct device *dev)
@@ -326,6 +349,10 @@ static void zram_meta_free(struct zram_meta *meta)
kfree(meta);
}
+static void rcu_zram_do_nothing(struct rcu_head *unused)
+{
+}
+
static struct zram_meta *zram_meta_alloc(int device_id, u64 disksize)
{
char pool_name[8];
@@ -726,11 +753,8 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
return;
}
- zcomp_destroy(zram->comp);
zram->max_comp_streams = 1;
- zram_meta_free(zram->meta);
- zram->meta = NULL;
/* Reset stats */
memset(&zram->stats, 0, sizeof(zram->stats));
@@ -738,8 +762,12 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
if (reset_capacity)
set_capacity(zram->disk, 0);
+ setup_init_done(zram, false);
+ call_srcu(&zram->srcu, &zram->rcu, rcu_zram_do_nothing);
+ synchronize_srcu(&zram->srcu);
+ zram_meta_free(zram->meta);
+ zcomp_destroy(zram->comp);
up_write(&zram->init_lock);
-
/*
* Revalidate disk out of the init_lock to avoid lockdep splat.
* It's okay because disk's capacity is protected by init_lock
@@ -762,10 +790,19 @@ static ssize_t disksize_store(struct device *dev,
if (!disksize)
return -EINVAL;
+ down_write(&zram->init_lock);
+ if (init_done(zram)) {
+ pr_info("Cannot change disksize for initialized device\n");
+ up_write(&zram->init_lock);
+ return -EBUSY;
+ }
+
disksize = PAGE_ALIGN(disksize);
meta = zram_meta_alloc(zram->disk->first_minor, disksize);
- if (!meta)
+ if (!meta) {
+ up_write(&zram->init_lock);
return -ENOMEM;
+ }
comp = zcomp_create(zram->compressor, zram->max_comp_streams);
if (IS_ERR(comp)) {
@@ -775,17 +812,11 @@ static ssize_t disksize_store(struct device *dev,
goto out_free_meta;
}
- down_write(&zram->init_lock);
- if (init_done(zram)) {
- pr_info("Cannot change disksize for initialized device\n");
- err = -EBUSY;
- goto out_destroy_comp;
- }
-
zram->meta = meta;
zram->comp = comp;
zram->disksize = disksize;
set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
+ setup_init_done(zram, true);
up_write(&zram->init_lock);
/*
@@ -797,10 +828,8 @@ static ssize_t disksize_store(struct device *dev,
return len;
-out_destroy_comp:
- up_write(&zram->init_lock);
- zcomp_destroy(comp);
out_free_meta:
+ up_write(&zram->init_lock);
zram_meta_free(meta);
return err;
}
@@ -905,9 +934,10 @@ out:
*/
static void zram_make_request(struct request_queue *queue, struct bio *bio)
{
+ int idx;
struct zram *zram = queue->queuedata;
- down_read(&zram->init_lock);
+ idx = srcu_read_lock(&zram->srcu);
if (unlikely(!init_done(zram)))
goto error;
@@ -918,12 +948,12 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
}
__zram_make_request(zram, bio);
- up_read(&zram->init_lock);
+ srcu_read_unlock(&zram->srcu, idx);
return;
error:
- up_read(&zram->init_lock);
+ srcu_read_unlock(&zram->srcu, idx);
bio_io_error(bio);
}
@@ -945,18 +975,20 @@ static void zram_slot_free_notify(struct block_device *bdev,
static int zram_rw_page(struct block_device *bdev, sector_t sector,
struct page *page, int rw)
{
- int offset, err;
+ int offset, err, idx;
u32 index;
struct zram *zram;
struct bio_vec bv;
zram = bdev->bd_disk->private_data;
+ idx = srcu_read_lock(&zram->srcu);
+
if (!valid_io_request(zram, sector, PAGE_SIZE)) {
atomic64_inc(&zram->stats.invalid_io);
+ srcu_read_unlock(&zram->srcu, idx);
return -EINVAL;
}
- down_read(&zram->init_lock);
if (unlikely(!init_done(zram))) {
err = -EIO;
goto out_unlock;
@@ -971,7 +1003,7 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
err = zram_bvec_rw(zram, &bv, index, offset, rw);
out_unlock:
- up_read(&zram->init_lock);
+ srcu_read_unlock(&zram->srcu, idx);
/*
* If I/O fails, just return error(ie, non-zero) without
* calling page_endio.
@@ -1041,6 +1073,11 @@ static int create_device(struct zram *zram, int device_id)
init_rwsem(&zram->init_lock);
+ if (init_srcu_struct(&zram->srcu)) {
+ pr_err("Error initialize srcu for device %d\n", device_id);
+ goto out;
+ }
+
zram->queue = blk_alloc_queue(GFP_KERNEL);
if (!zram->queue) {
pr_err("Error allocating disk queue for device %d\n",
@@ -1125,8 +1162,8 @@ static void destroy_device(struct zram *zram)
del_gendisk(zram->disk);
put_disk(zram->disk);
-
blk_cleanup_queue(zram->queue);
+ cleanup_srcu_struct(&zram->srcu);
}
static int __init zram_init(void)
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index e492f6bf11f1..2042c310aea8 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -105,8 +105,13 @@ struct zram {
struct gendisk *disk;
struct zcomp *comp;
+ struct srcu_struct srcu;
+ struct rcu_head rcu;
+
/* Prevent concurrent execution of device init, reset and R/W request */
struct rw_semaphore init_lock;
+ bool init_done;
+
/*
* This is the limit on amount of *uncompressed* worth of data
* we can store in a disk.
--
1.9.1
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