kernel/linux.git/drivers/md/bcache/writeback.c, branch linux-5.11.y

bcache: fix race between setting bdev state to none and new write request direct to backing

2020-12-07T20:25:16+00:00

There is a race condition in detaching as below: A. detaching B. Write request (1) writing back (2) write back done, set bdev state to clean. (3) cached_dev_put() and schedule_work(&dc->detach); (4) write data [0 - 4K] directly into backing and ack to user. (5) power-failure... When we restart this bcache device, this bdev is clean but not detached, and read [0 - 4K], we will get unexpected old data from cache device. To fix this problem, set the bdev state to none when we writeback done in detaching, and then if power-failure happened as above, the data in cache will not be used in next bcache device starting, it's detached, we will read the correct data from backing derectly. Signed-off-by: Dongsheng Yang Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: remove embedded struct cache_sb from struct cache_set

2020-10-02T20:25:30+00:00

Since bcache code was merged into mainline kerrnel, each cache set only as one single cache in it. The multiple caches framework is here but the code is far from completed. Considering the multiple copies of cached data can also be stored on e.g. md raid1 devices, it is unnecessary to support multiple caches in one cache set indeed. The previous preparation patches fix the dependencies of explicitly making a cache set only have single cache. Now we don't have to maintain an embedded partial super block in struct cache_set, the in-memory super block can be directly referenced from struct cache. This patch removes the embedded struct cache_sb from struct cache_set, and fixes all locations where the superb lock was referenced from this removed super block by referencing the in-memory super block of struct cache. Signed-off-by: Coly Li Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

bcache: fix overflow in offset_to_stripe()

2020-07-25T13:38:20+00:00

offset_to_stripe() returns the stripe number (in type unsigned int) from an offset (in type uint64_t) by the following calculation, do_div(offset, d->stripe_size); For large capacity backing device (e.g. 18TB) with small stripe size (e.g. 4KB), the result is 4831838208 and exceeds UINT_MAX. The actual returned value which caller receives is 536870912, due to the overflow. Indeed in bcache_device_init(), bcache_device->nr_stripes is limited in range [1, INT_MAX]. Therefore all valid stripe numbers in bcache are in range [0, bcache_dev->nr_stripes - 1]. This patch adds a upper limition check in offset_to_stripe(): the max valid stripe number should be less than bcache_device->nr_stripes. If the calculated stripe number from do_div() is equal to or larger than bcache_device->nr_stripe, -EINVAL will be returned. (Normally nr_stripes is less than INT_MAX, exceeding upper limitation doesn't mean overflow, therefore -EOVERFLOW is not used as error code.) This patch also changes nr_stripes' type of struct bcache_device from 'unsigned int' to 'int', and return value type of offset_to_stripe() from 'unsigned int' to 'int', to match their exact data ranges. All locations where bcache_device->nr_stripes and offset_to_stripe() are referenced also get updated for the above type change. Reported-and-tested-by: Ken Raeburn Signed-off-by: Coly Li Cc: stable@vger.kernel.org Link: https://bugzilla.redhat.com/show_bug.cgi?id=1783075 Signed-off-by: Jens Axboe

bcache: Use struct_size() in kzalloc()

2020-07-25T13:38:20+00:00

Make use of the struct_size() helper instead of an open-coded version in order to avoid any potential type mistakes. This code was detected with the help of Coccinelle and, audited and fixed manually. Signed-off-by: Gustavo A. R. Silva Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: writeback: Remove unneeded variable i

2020-07-25T13:38:20+00:00

Remove unneeded variable i in bch_dirty_init_thread(). Signed-off-by: Xu Wang Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: Convert pr_ uses to a more typical style

2020-05-27T11:19:36+00:00

Remove the trailing newline from the define of pr_fmt and add newlines to the uses. Miscellanea: o Convert bch_bkey_dump from multiple uses of pr_err to pr_cont as the earlier conversion was inappropriate done causing multiple lines to be emitted where only a single output line was desired o Use vsprintf extension %pV in bch_cache_set_error to avoid multiple line output where only a single line output was desired o Coalesce formats Fixes: 6ae63e3501c4 ("bcache: replace printk() by pr_*() routines") Signed-off-by: Joe Perches Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: optimize barrier usage for atomic operations

2020-03-22T16:06:57+00:00

The idea of this patch is from Davidlohr Bueso, he posts a patch for bcache to optimize barrier usage for read-modify-write atomic bitops. Indeed such optimization can also apply on other locations where smp_mb() is used before or after an atomic operation. This patch replaces smp_mb() with smp_mb__before_atomic() or smp_mb__after_atomic() in btree.c and writeback.c, where it is used to synchronize memory cache just earlier on other cores. Although the locations are not on hot code path, it is always not bad to mkae things a little better. Signed-off-by: Coly Li Cc: Davidlohr Bueso Signed-off-by: Jens Axboe

bcache: optimize barrier usage for Rmw atomic bitops

2020-03-22T16:06:57+00:00

We can avoid the unnecessary barrier on non LL/SC architectures, such as x86. Instead, use the smp_mb__after_atomic(). Signed-off-by: Davidlohr Bueso Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: make bch_sectors_dirty_init() to be multithreaded

2020-03-22T16:06:57+00:00

When attaching a cached device (a.k.a backing device) to a cache device, bch_sectors_dirty_init() is called to count dirty sectors and stripes (see what bcache_dev_sectors_dirty_add() does) on the cache device. The counting is done by a single thread recursive function bch_btree_map_keys() to iterate all the bcache btree nodes. If the btree has huge number of nodes, bch_sectors_dirty_init() will take quite long time. In my testing, if the registering cache set has a existed UUID which matches a already registered cached device, the automatical attachment during the registration may take more than 55 minutes. This is too long for waiting the bcache to work in real deployment. Fortunately when bch_sectors_dirty_init() is called, no other thread will access the btree yet, it is safe to do a read-only parallelized dirty sectors counting by multiple threads. This patch tries to create multiple threads, and each thread tries to one-by-one count dirty sectors from the sub-tree indexed by a root node key which the thread fetched. After the sub-tree is counted, the counting thread will continue to fetch another root node key, until the fetched key is NULL. How many threads in parallel depends on the number of keys from the btree root node, and the number of online CPU core. The thread number will be the less number but no more than BCH_DIRTY_INIT_THRD_MAX. If there are only 2 keys in root node, it can only be 2x times faster by this patch. But if there are 10 keys in the root node, with this patch it can be 10x times faster. Signed-off-by: Coly Li Cc: Christoph Hellwig Signed-off-by: Jens Axboe

bcache: add idle_max_writeback_rate sysfs interface

2019-11-13T22:42:50+00:00

For writeback mode, if there is no regular I/O request for a while, the writeback rate will be set to the maximum value (1TB/s for now). This is good for most of the storage workload, but there are still people don't what the maximum writeback rate in I/O idle time. This patch adds a sysfs interface file idle_max_writeback_rate to permit people to disable maximum writeback rate. Then the minimum writeback rate can be advised by writeback_rate_minimum in the bcache device's sysfs interface. Reported-by: Christian Balzer Signed-off-by: Coly Li Signed-off-by: Jens Axboe