On Thu, Nov 22, 2012 at 12:13:24PM +0100, Jerome Marchand wrote: > 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. That's not a only swap case. Let's think following usecase. 1) Booting 2) echo $((DISKSIZE)) > /sys/block/zram0/disksize 3) dd if=/dev/zero of=/dev/zram0 bs=4K count=1 4) Written 4K page(page-A) is still page cache and isn't submitted to zram block device. 5) Memory pressure happen by some memory hogger. 6) VM start to reclaim and write page-A to zram0. 7) zram_init_device is called at last. 8) allocate GFP_KERNEL in zram_init_device 9) goto reclaim path again. 10) deadlock. So I think it's not false positive. Even if it is, I think lock split isn't a good idea to just avoid lockdep warn. It makes code unnecessary complicated and it would be more error-prone. Let's not add another lock without performance trouble report by the lock. As I discussed with Nitin in this thread, lazy initialization don't have much point and disksize setting option isn't consistent for user behavior. And I expect Nitin will send patch "diet of table" soonish. So just moving the initialzation part from reclaim context to process's one is simple and clear solution, I believe. > > The following (quickly tested) patch should prevent lockdep complain. > > Jerome > > --- > >From ebb3514c4ee18276da7c5ca08025991b493ac204 Mon Sep 17 00:00:00 2001 > From: Jerome Marchand <jmarchan@xxxxxxxxxx> > 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@xxxxxxxxxx> > --- > 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 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>