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@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. 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