user/sven/linux.git/drivers/md/bcache/alloc.c, branch v5.5.11

bcache: fix deadlock in bcache_allocator

2019-11-13T22:42:50Z

bcache_allocator can call the following: bch_allocator_thread() -> bch_prio_write() -> bch_bucket_alloc() -> wait on &ca->set->bucket_wait But the wake up event on bucket_wait is supposed to come from bch_allocator_thread() itself => deadlock: [ 1158.490744] INFO: task bcache_allocato:15861 blocked for more than 10 seconds. [ 1158.495929] Not tainted 5.3.0-050300rc3-generic #201908042232 [ 1158.500653] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 1158.504413] bcache_allocato D 0 15861 2 0x80004000 [ 1158.504419] Call Trace: [ 1158.504429] __schedule+0x2a8/0x670 [ 1158.504432] schedule+0x2d/0x90 [ 1158.504448] bch_bucket_alloc+0xe5/0x370 [bcache] [ 1158.504453] ? wait_woken+0x80/0x80 [ 1158.504466] bch_prio_write+0x1dc/0x390 [bcache] [ 1158.504476] bch_allocator_thread+0x233/0x490 [bcache] [ 1158.504491] kthread+0x121/0x140 [ 1158.504503] ? invalidate_buckets+0x890/0x890 [bcache] [ 1158.504506] ? kthread_park+0xb0/0xb0 [ 1158.504510] ret_from_fork+0x35/0x40 Fix by making the call to bch_prio_write() non-blocking, so that bch_allocator_thread() never waits on itself. Moreover, make sure to wake up the garbage collector thread when bch_prio_write() is failing to allocate buckets. BugLink: https://bugs.launchpad.net/bugs/1784665 BugLink: https://bugs.launchpad.net/bugs/1796292 Signed-off-by: Andrea Righi Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: check CACHE_SET_IO_DISABLE in allocator code

2019-06-28T13:39:15Z

If CACHE_SET_IO_DISABLE of a cache set flag is set by too many I/O errors, currently allocator routines can still continue allocate space which may introduce inconsistent metadata state. This patch checkes CACHE_SET_IO_DISABLE bit in following allocator routines, - bch_bucket_alloc() - __bch_bucket_alloc_set() Once CACHE_SET_IO_DISABLE is set on cache set, the allocator routines may reject allocation request earlier to avoid potential inconsistent metadata. Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: avoid clang -Wunintialized warning

2019-04-24T16:56:27Z

clang has identified a code path in which it thinks a variable may be unused: drivers/md/bcache/alloc.c:333:4: error: variable 'bucket' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized] fifo_pop(&ca->free_inc, bucket); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ drivers/md/bcache/util.h:219:27: note: expanded from macro 'fifo_pop' #define fifo_pop(fifo, i) fifo_pop_front(fifo, (i)) ^~~~~~~~~~~~~~~~~~~~~~~~~ drivers/md/bcache/util.h:189:6: note: expanded from macro 'fifo_pop_front' if (_r) { \ ^~ drivers/md/bcache/alloc.c:343:46: note: uninitialized use occurs here allocator_wait(ca, bch_allocator_push(ca, bucket)); ^~~~~~ drivers/md/bcache/alloc.c:287:7: note: expanded from macro 'allocator_wait' if (cond) \ ^~~~ drivers/md/bcache/alloc.c:333:4: note: remove the 'if' if its condition is always true fifo_pop(&ca->free_inc, bucket); ^ drivers/md/bcache/util.h:219:27: note: expanded from macro 'fifo_pop' #define fifo_pop(fifo, i) fifo_pop_front(fifo, (i)) ^ drivers/md/bcache/util.h:189:2: note: expanded from macro 'fifo_pop_front' if (_r) { \ ^ drivers/md/bcache/alloc.c:331:15: note: initialize the variable 'bucket' to silence this warning long bucket; ^ This cannot happen in practice because we only enter the loop if there is at least one element in the list. Slightly rearranging the code makes this clearer to both the reader and the compiler, which avoids the warning. Signed-off-by: Arnd Bergmann Reviewed-by: Nathan Chancellor Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: use MAX_CACHES_PER_SET instead of magic number 8 in __bch_bucket_alloc_set

2018-10-08T14:19:56Z

Current cache_set has MAX_CACHES_PER_SET caches most, and the macro is used for " struct cache *cache_by_alloc[MAX_CACHES_PER_SET]; " in the define of struct cache_set. Use MAX_CACHES_PER_SET instead of magic number 8 in __bch_bucket_alloc_set. Signed-off-by: Shenghui Wang Signed-off-by: Coly Li Signed-off-by: Jens Axboe

bcache: style fix to add a blank line after declarations

2018-08-11T21:46:41Z

Signed-off-by: Coly Li Reviewed-by: Shenghui Wang Signed-off-by: Jens Axboe

bcache: style fix to replace 'unsigned' by 'unsigned int'

2018-08-11T21:46:41Z

This patch fixes warning reported by checkpatch.pl by replacing 'unsigned' with 'unsigned int'. Signed-off-by: Coly Li Reviewed-by: Shenghui Wang Signed-off-by: Jens Axboe

bcache: add wait_for_kthread_stop() in bch_allocator_thread()

2018-05-03T14:35:13Z

When CACHE_SET_IO_DISABLE is set on cache set flags, bcache allocator thread routine bch_allocator_thread() may stop the while-loops and exit. Then it is possible to observe the following kernel oops message, [ 631.068366] bcache: bch_btree_insert() error -5 [ 631.069115] bcache: cached_dev_detach_finish() Caching disabled for sdf [ 631.070220] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 [ 631.070250] PGD 0 P4D 0 [ 631.070261] Oops: 0002 [#1] SMP PTI [snipped] [ 631.070578] Workqueue: events cache_set_flush [bcache] [ 631.070597] RIP: 0010:exit_creds+0x1b/0x50 [ 631.070610] RSP: 0018:ffffc9000705fe08 EFLAGS: 00010246 [ 631.070626] RAX: 0000000000000001 RBX: ffff880a622ad300 RCX: 000000000000000b [ 631.070645] RDX: 0000000000000601 RSI: 000000000000000c RDI: 0000000000000000 [ 631.070663] RBP: ffff880a622ad300 R08: ffffea00190c66e0 R09: 0000000000000200 [ 631.070682] R10: ffff880a48123000 R11: ffff880000000000 R12: 0000000000000000 [ 631.070700] R13: ffff880a4b160e40 R14: ffff880a4b160000 R15: 0ffff880667e2530 [ 631.070719] FS: 0000000000000000(0000) GS:ffff880667e00000(0000) knlGS:0000000000000000 [ 631.070740] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 631.070755] CR2: 0000000000000000 CR3: 000000000200a001 CR4: 00000000003606e0 [ 631.070774] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 631.070793] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 631.070811] Call Trace: [ 631.070828] __put_task_struct+0x55/0x160 [ 631.070845] kthread_stop+0xee/0x100 [ 631.070863] cache_set_flush+0x11d/0x1a0 [bcache] [ 631.070879] process_one_work+0x146/0x340 [ 631.070892] worker_thread+0x47/0x3e0 [ 631.070906] kthread+0xf5/0x130 [ 631.070917] ? max_active_store+0x60/0x60 [ 631.070930] ? kthread_bind+0x10/0x10 [ 631.070945] ret_from_fork+0x35/0x40 [snipped] [ 631.071017] RIP: exit_creds+0x1b/0x50 RSP: ffffc9000705fe08 [ 631.071033] CR2: 0000000000000000 [ 631.071045] ---[ end trace 011c63a24b22c927 ]--- [ 631.071085] bcache: bcache_device_free() bcache0 stopped The reason is when cache_set_flush() tries to call kthread_stop() to stop allocator thread, but it exits already due to cache device I/O errors. This patch adds wait_for_kthread_stop() at tail of bch_allocator_thread(), to prevent the thread routine exiting directly. Then the allocator thread can be blocked at wait_for_kthread_stop() and wait for cache_set_flush() to stop it by calling kthread_stop(). changelog: v3: add Reviewed-by from Hannnes. v2: not directly return from allocator_wait(), move 'return 0' to tail of bch_allocator_thread(). v1: initial version. Fixes: 771f393e8ffc ("bcache: add CACHE_SET_IO_DISABLE to struct cache_set flags") Signed-off-by: Coly Li Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

bcache: add CACHE_SET_IO_DISABLE to struct cache_set flags

2018-03-19T02:15:20Z

When too many I/Os failed on cache device, bch_cache_set_error() is called in the error handling code path to retire whole problematic cache set. If new I/O requests continue to come and take refcount dc->count, the cache set won't be retired immediately, this is a problem. Further more, there are several kernel thread and self-armed kernel work may still running after bch_cache_set_error() is called. It needs to wait quite a while for them to stop, or they won't stop at all. They also prevent the cache set from being retired. The solution in this patch is, to add per cache set flag to disable I/O request on this cache and all attached backing devices. Then new coming I/O requests can be rejected in *_make_request() before taking refcount, kernel threads and self-armed kernel worker can stop very fast when flags bit CACHE_SET_IO_DISABLE is set. Because bcache also do internal I/Os for writeback, garbage collection, bucket allocation, journaling, this kind of I/O should be disabled after bch_cache_set_error() is called. So closure_bio_submit() is modified to check whether CACHE_SET_IO_DISABLE is set on cache_set->flags. If set, closure_bio_submit() will set bio->bi_status to BLK_STS_IOERR and return, generic_make_request() won't be called. A sysfs interface is also added to set or clear CACHE_SET_IO_DISABLE bit from cache_set->flags, to disable or enable cache set I/O for debugging. It is helpful to trigger more corner case issues for failed cache device. Changelog v4, add wait_for_kthread_stop(), and call it before exits writeback and gc kernel threads. v3, change CACHE_SET_IO_DISABLE from 4 to 3, since it is bit index. remove "bcache: " prefix when printing out kernel message. v2, more changes by previous review, - Use CACHE_SET_IO_DISABLE of cache_set->flags, suggested by Junhui. - Check CACHE_SET_IO_DISABLE in bch_btree_gc() to stop a while-loop, this is reported and inspired from origal patch of Pavel Vazharov. v1, initial version. Signed-off-by: Coly Li Reviewed-by: Hannes Reinecke Reviewed-by: Michael Lyle Cc: Junhui Tang Cc: Michael Lyle Cc: Pavel Vazharov Signed-off-by: Jens Axboe

bcache: properly set task state in bch_writeback_thread()

2018-02-07T19:50:01Z

Kernel thread routine bch_writeback_thread() has the following code block, 447 down_write(&dc->writeback_lock); 448~450 if (check conditions) { 451 up_write(&dc->writeback_lock); 452 set_current_state(TASK_INTERRUPTIBLE); 453 454 if (kthread_should_stop()) 455 return 0; 456 457 schedule(); 458 continue; 459 } If condition check is true, its task state is set to TASK_INTERRUPTIBLE and call schedule() to wait for others to wake up it. There are 2 issues in current code, 1, Task state is set to TASK_INTERRUPTIBLE after the condition checks, if another process changes the condition and call wake_up_process(dc-> writeback_thread), then at line 452 task state is set back to TASK_INTERRUPTIBLE, the writeback kernel thread will lose a chance to be waken up. 2, At line 454 if kthread_should_stop() is true, writeback kernel thread will return to kernel/kthread.c:kthread() with TASK_INTERRUPTIBLE and call do_exit(). It is not good to enter do_exit() with task state TASK_INTERRUPTIBLE, in following code path might_sleep() is called and a warning message is reported by __might_sleep(): "WARNING: do not call blocking ops when !TASK_RUNNING; state=1 set at [xxxx]". For the first issue, task state should be set before condition checks. Ineed because dc->writeback_lock is required when modifying all the conditions, calling set_current_state() inside code block where dc-> writeback_lock is hold is safe. But this is quite implicit, so I still move set_current_state() before all the condition checks. For the second issue, frankley speaking it does not hurt when kernel thread exits with TASK_INTERRUPTIBLE state, but this warning message scares users, makes them feel there might be something risky with bcache and hurt their data. Setting task state to TASK_RUNNING before returning fixes this problem. In alloc.c:allocator_wait(), there is also a similar issue, and is also fixed in this patch. Changelog: v3: merge two similar fixes into one patch v2: fix the race issue in v1 patch. v1: initial buggy fix. Signed-off-by: Coly Li Reviewed-by: Hannes Reinecke Reviewed-by: Michael Lyle Cc: Michael Lyle Cc: Junhui Tang Signed-off-by: Jens Axboe

bcache: segregate flash only volume write streams

2018-01-08T20:29:00Z

In such scenario that there are some flash only volumes , and some cached devices, when many tasks request these devices in writeback mode, the write IOs may fall to the same bucket as bellow: | cached data | flash data | cached data | cached data| flash data| then after writeback of these cached devices, the bucket would be like bellow bucket: | free | flash data | free | free | flash data | So, there are many free space in this bucket, but since data of flash only volumes still exists, so this bucket cannot be reclaimable, which would cause waste of bucket space. In this patch, we segregate flash only volume write streams from cached devices, so data from flash only volumes and cached devices can store in different buckets. Compare to v1 patch, this patch do not add a additionally open bucket list, and it is try best to segregate flash only volume write streams from cached devices, sectors of flash only volumes may still be mixed with dirty sectors of cached device, but the number is very small. [mlyle: fixed commit log formatting, permissions, line endings] Signed-off-by: Tang Junhui Reviewed-by: Michael Lyle Signed-off-by: Michael Lyle Signed-off-by: Jens Axboe