From c5bde2388e5b77b39db1b615e2deda2c535f6f60 Mon Sep 17 00:00:00 2001 From: Jerome Marchand Date: Fri, 10 Jun 2011 15:28:49 +0200 Subject: [PATCH] Staging: zram: Replace mutex lock by a R/W semaphore Currently, nothing protects zram table from concurrent access. For instance, ZRAM_UNCOMPRESSED bit can be cleared by zram_free_page() called from a concurrent write between the time ZRAM_UNCOMPRESSED has been set and the time it is tested to unmap KM_USER0 in zram_bvec_write(). This ultimately leads to kernel panic. Also, a read request can occurs when the page has been freed by a running write request and before it has been updated, leading to zero filled block being incorrectly read and "Read before write" error message. This patch replace the current mutex by a rw_semaphore. It extends the protection to zram table (currently, only compression buffers are protected) and read requests (currently, only write requests are protected). Signed-off-by: Jerome Marchand Signed-off-by: Greg Kroah-Hartman --- drivers/staging/zram/zram_drv.c | 25 +++++++++++++------------ drivers/staging/zram/zram_drv.h | 4 ++-- 2 files changed, 15 insertions(+), 14 deletions(-) diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c index 54ad29d..c5fdc55 100644 --- a/drivers/staging/zram/zram_drv.c +++ b/drivers/staging/zram/zram_drv.c @@ -359,8 +359,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index, zram_test_flag(zram, index, ZRAM_ZERO)) zram_free_page(zram, index); - mutex_lock(&zram->lock); - user_mem = kmap_atomic(page, KM_USER0); if (is_partial_io(bvec)) @@ -371,7 +369,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index, if (page_zero_filled(uncmem)) { kunmap_atomic(user_mem, KM_USER0); - mutex_unlock(&zram->lock); if (is_partial_io(bvec)) kfree(uncmem); zram_stat_inc(&zram->stats.pages_zero); @@ -388,7 +385,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index, kfree(uncmem); if (unlikely(ret != LZO_E_OK)) { - mutex_unlock(&zram->lock); pr_err("Compression failed! err=%d\n", ret); goto out; } @@ -402,7 +398,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index, clen = PAGE_SIZE; page_store = alloc_page(GFP_NOIO | __GFP_HIGHMEM); if (unlikely(!page_store)) { - mutex_unlock(&zram->lock); pr_info("Error allocating memory for " "incompressible page: %u\n", index); ret = -ENOMEM; @@ -420,7 +415,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index, if (xv_malloc(zram->mem_pool, clen + sizeof(*zheader), &zram->table[index].page, &store_offset, GFP_NOIO | __GFP_HIGHMEM)) { - mutex_unlock(&zram->lock); pr_info("Error allocating memory for compressed " "page: %u, size=%zu\n", index, clen); ret = -ENOMEM; @@ -454,8 +448,6 @@ memstore: if (clen <= PAGE_SIZE / 2) zram_stat_inc(&zram->stats.good_compress); - mutex_unlock(&zram->lock); - return 0; out: @@ -467,10 +459,19 @@ out: static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index, int offset, struct bio *bio, int rw) { - if (rw == READ) - return zram_bvec_read(zram, bvec, index, offset, bio); + int ret; - return zram_bvec_write(zram, bvec, index, offset); + if (rw == READ) { + down_read(&zram->lock); + ret = zram_bvec_read(zram, bvec, index, offset, bio); + up_read(&zram->lock); + } else { + down_write(&zram->lock); + ret = zram_bvec_write(zram, bvec, index, offset); + up_write(&zram->lock); + } + + return ret; } static void update_position(u32 *index, int *offset, struct bio_vec *bvec) @@ -701,7 +702,7 @@ static int create_device(struct zram *zram, int device_id) { int ret = 0; - mutex_init(&zram->lock); + init_rwsem(&zram->lock); mutex_init(&zram->init_lock); spin_lock_init(&zram->stat64_lock); diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h index 8acf9eb..abe5221 100644 --- a/drivers/staging/zram/zram_drv.h +++ b/drivers/staging/zram/zram_drv.h @@ -107,8 +107,8 @@ struct zram { void *compress_buffer; struct table *table; spinlock_t stat64_lock; /* protect 64-bit stats */ - struct mutex lock; /* protect compression buffers against - * concurrent writes */ + struct rw_semaphore lock; /* protect compression buffers and table + * against concurrent read and writes */ struct request_queue *queue; struct gendisk *disk; int init_done; -- 2.7.4