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Date: Thu, 22 Nov 2012 12:13:24 +0100
From: Jerome Marchand <jmarchan@...hat.com>
To: Minchan Kim <minchan@...nel.org>
CC: Nitin Gupta <ngupta@...are.org>,
Seth Jennings <sjenning@...ux.vnet.ibm.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Pekka Enberg <penberg@...helsinki.fi>,
Konrad Rzeszutek Wilk <konrad@...nok.org>,
Dan Magenheimer <dan.magenheimer@...cle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: Lockdep complain for zram
On 11/21/2012 09:37 AM, Minchan Kim wrote:
> Hi alls,
>
> Today, I saw below complain of lockdep.
> As a matter of fact, I knew it long time ago but forgot that.
> The reason lockdep complains is that now zram uses GFP_KERNEL
> in reclaim path(ex, __zram_make_request) :(
> I can fix it via replacing GFP_KERNEL with GFP_NOIO.
> But more big problem is vzalloc in zram_init_device which calls GFP_KERNEL.
> Of course, I can change it with __vmalloc which can receive gfp_t.
> But still we have a problem. Althoug __vmalloc can handle gfp_t, it calls
> allocation of GFP_KERNEL. That's why I sent the patch.
> https://lkml.org/lkml/2012/4/23/77
> Since then, I forgot it, saw the bug today and poped the question again.
>
> Yes. Fundamental problem is utter crap API vmalloc.
> If we can fix it, everyone would be happy. But life isn't simple like seeing
> my thread of the patch.
>
> So next option is to move zram_init_device into setting disksize time.
> But it makes unnecessary metadata waste until zram is used really(That's why
> Nitin move zram_init_device from disksize setting time to make_request) and
> it makes user should set the disksize before using, which are behavior change.
>
> I would like to clean up this issue before promoting because it might change
> usage behavior.
>
> Do you have any idea?
This is a false positive due to the memory allocation in
zram_init_device() called from zram_make_request(). It appears to
lockdep that the allocation might trigger a request on the device that
would try to take init_lock again, but in fact it doesn't. The device
is not initialized yet, even less swapped on.
The following (quickly tested) patch should prevent lockdep complain.
Jerome
---
>From ebb3514c4ee18276da7c5ca08025991b493ac204 Mon Sep 17 00:00:00 2001
From: Jerome Marchand <jmarchan@...hat.com>
Date: Thu, 22 Nov 2012 09:07:40 +0100
Subject: [PATCH] staging: zram: Avoid lockdep warning
zram triggers a lockdep warning. The cause of it is the call to
zram_init_device() from zram_make_request(). The memory allocation in
zram_init_device() could start a memory reclaim which in turn could
cause swapout and (as it appears to lockdep) a call to
zram_make_request(). However this is a false positive: an
unititialized device can't be used as swap.
A solution is to split init_lock in two lock. One mutex that protects
init, reset and size setting and a rw_semaphore that protects requests
and reset. Thus init and request would be protected by different locks
and lockdep will be happy.
Signed-off-by: Jerome Marchand <jmarchan@...hat.com>
---
drivers/staging/zram/zram_drv.c | 41 +++++++++++++++++++-----------------
drivers/staging/zram/zram_drv.h | 16 ++++++++++---
drivers/staging/zram/zram_sysfs.c | 20 +++++++++---------
3 files changed, 44 insertions(+), 33 deletions(-)
diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index fb4a7c9..b3bc3c4 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -470,11 +470,11 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
{
struct zram *zram = queue->queuedata;
- if (unlikely(!zram->init_done) && zram_init_device(zram))
+ if (unlikely(!is_initialized(zram)) && zram_init_device(zram))
goto error;
- down_read(&zram->init_lock);
- if (unlikely(!zram->init_done))
+ down_read(&zram->req_lock);
+ if (unlikely(!is_initialized(zram)))
goto error_unlock;
if (!valid_io_request(zram, bio)) {
@@ -483,12 +483,12 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
}
__zram_make_request(zram, bio, bio_data_dir(bio));
- up_read(&zram->init_lock);
+ up_read(&zram->req_lock);
return;
error_unlock:
- up_read(&zram->init_lock);
+ up_read(&zram->req_lock);
error:
bio_io_error(bio);
}
@@ -497,7 +497,7 @@ void __zram_reset_device(struct zram *zram)
{
size_t index;
- zram->init_done = 0;
+ atomic_set(&zram->init_done, 0);
/* Free various per-device buffers */
kfree(zram->compress_workmem);
@@ -529,9 +529,12 @@ void __zram_reset_device(struct zram *zram)
void zram_reset_device(struct zram *zram)
{
- down_write(&zram->init_lock);
- __zram_reset_device(zram);
- up_write(&zram->init_lock);
+ mutex_lock(&zram->init_lock);
+ down_write(&zram->req_lock);
+ if (is_initialized(zram))
+ __zram_reset_device(zram);
+ up_write(&zram->req_lock);
+ mutex_unlock(&zram->init_lock);
}
int zram_init_device(struct zram *zram)
@@ -539,10 +542,10 @@ int zram_init_device(struct zram *zram)
int ret;
size_t num_pages;
- down_write(&zram->init_lock);
+ mutex_lock(&zram->init_lock);
- if (zram->init_done) {
- up_write(&zram->init_lock);
+ if (is_initialized(zram)) {
+ mutex_unlock(&zram->init_lock);
return 0;
}
@@ -583,8 +586,8 @@ int zram_init_device(struct zram *zram)
goto fail;
}
- zram->init_done = 1;
- up_write(&zram->init_lock);
+ atomic_set(&zram->init_done, 1);
+ mutex_unlock(&zram->init_lock);
pr_debug("Initialization done!\n");
return 0;
@@ -594,7 +597,7 @@ fail_no_table:
zram->disksize = 0;
fail:
__zram_reset_device(zram);
- up_write(&zram->init_lock);
+ mutex_unlock(&zram->init_lock);
pr_err("Initialization failed: err=%d\n", ret);
return ret;
}
@@ -619,7 +622,8 @@ static int create_device(struct zram *zram, int device_id)
int ret = 0;
init_rwsem(&zram->lock);
- init_rwsem(&zram->init_lock);
+ mutex_init(&zram->init_lock);
+ init_rwsem(&zram->req_lock);
spin_lock_init(&zram->stat64_lock);
zram->queue = blk_alloc_queue(GFP_KERNEL);
@@ -672,7 +676,7 @@ static int create_device(struct zram *zram, int device_id)
goto out;
}
- zram->init_done = 0;
+ atomic_set(&zram->init_done, 0);
out:
return ret;
@@ -755,8 +759,7 @@ static void __exit zram_exit(void)
zram = &zram_devices[i];
destroy_device(zram);
- if (zram->init_done)
- zram_reset_device(zram);
+ zram_reset_device(zram);
}
unregister_blkdev(zram_major, "zram");
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index df2eec4..f6bcead 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -96,9 +96,12 @@ struct zram {
* against concurrent read and writes */
struct request_queue *queue;
struct gendisk *disk;
- int init_done;
- /* Prevent concurrent execution of device init, reset and R/W request */
- struct rw_semaphore init_lock;
+ atomic_t init_done;
+ /* Prevent concurrent execution of device init, reset and
+ * disksize_store */
+ struct mutex init_lock;
+ /* Prevent concurent execution device reset and R/W requests */
+ struct rw_semaphore req_lock;
/*
* This is the limit on amount of *uncompressed* worth of data
* we can store in a disk.
@@ -108,6 +111,11 @@ struct zram {
struct zram_stats stats;
};
+static inline int is_initialized(struct zram *zram)
+{
+ return atomic_read(&zram->init_done);
+}
+
extern struct zram *zram_devices;
unsigned int zram_get_num_devices(void);
#ifdef CONFIG_SYSFS
@@ -115,6 +123,6 @@ extern struct attribute_group zram_disk_attr_group;
#endif
extern int zram_init_device(struct zram *zram);
-extern void __zram_reset_device(struct zram *zram);
+extern void zram_reset_device(struct zram *zram);
#endif
diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index de1eacf..b300881 100644
--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -62,16 +62,19 @@ static ssize_t disksize_store(struct device *dev,
if (!disksize)
return -EINVAL;
- down_write(&zram->init_lock);
- if (zram->init_done) {
- up_write(&zram->init_lock);
+ mutex_lock(&zram->init_lock);
+ down_write(&zram->req_lock);
+ if (is_initialized(zram)) {
+ up_write(&zram->req_lock);
+ mutex_unlock(&zram->init_lock);
pr_info("Cannot change disksize for initialized device\n");
return -EBUSY;
}
zram->disksize = PAGE_ALIGN(disksize);
set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
- up_write(&zram->init_lock);
+ up_write(&zram->req_lock);
+ mutex_unlock(&zram->init_lock);
return len;
}
@@ -81,7 +84,7 @@ static ssize_t initstate_show(struct device *dev,
{
struct zram *zram = dev_to_zram(dev);
- return sprintf(buf, "%u\n", zram->init_done);
+ return sprintf(buf, "%u\n", atomic_read(&zram->init_done));
}
static ssize_t reset_store(struct device *dev,
@@ -110,10 +113,7 @@ static ssize_t reset_store(struct device *dev,
if (bdev)
fsync_bdev(bdev);
- down_write(&zram->init_lock);
- if (zram->init_done)
- __zram_reset_device(zram);
- up_write(&zram->init_lock);
+ zram_reset_device(zram);
return len;
}
@@ -186,7 +186,7 @@ static ssize_t mem_used_total_show(struct device *dev,
u64 val = 0;
struct zram *zram = dev_to_zram(dev);
- if (zram->init_done)
+ if (is_initialized(zram))
val = zs_get_total_size_bytes(zram->mem_pool);
return sprintf(buf, "%llu\n", val);
--
1.7.7.6
--
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