From: Mike Snitzer Date: Fri, 20 Dec 2013 19:27:28 +0000 (-0500) Subject: dm thin: fix set_pool_mode exposed pool operation races X-Git-Tag: v3.14-rc1~130^2~18 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8b64e881eb40ac8b9bfcbce068a97eef819044ee;p=pandora-kernel.git dm thin: fix set_pool_mode exposed pool operation races The pool mode must not be switched until after the corresponding pool process_* methods have been established. Otherwise, because set_pool_mode() isn't interlocked with the IO path for performance reasons, the IO path can end up executing process_* operations that don't match the mode. This patch eliminates problems like the following (as seen on really fast PCIe SSD storage when transitioning the pool's mode from PM_READ_ONLY to PM_WRITE): kernel: device-mapper: thin: 253:2: reached low water mark for data device: sending event. kernel: device-mapper: thin: 253:2: no free data space available. kernel: device-mapper: thin: 253:2: switching pool to read-only mode kernel: device-mapper: thin: 253:2: switching pool to write mode kernel: ------------[ cut here ]------------ kernel: WARNING: CPU: 11 PID: 7564 at drivers/md/dm-thin.c:995 handle_unserviceable_bio+0x146/0x160 [dm_thin_pool]() ... kernel: Workqueue: dm-thin do_worker [dm_thin_pool] kernel: 00000000000003e3 ffff880308831cc8 ffffffff8152ebcb 00000000000003e3 kernel: 0000000000000000 ffff880308831d08 ffffffff8104c46c ffff88032502a800 kernel: ffff880036409000 ffff88030ec7ce00 0000000000000001 00000000ffffffc3 kernel: Call Trace: kernel: [] dump_stack+0x49/0x5e kernel: [] warn_slowpath_common+0x8c/0xc0 kernel: [] warn_slowpath_null+0x1a/0x20 kernel: [] handle_unserviceable_bio+0x146/0x160 [dm_thin_pool] kernel: [] process_bio_read_only+0x136/0x180 [dm_thin_pool] kernel: [] process_deferred_bios+0xc5/0x230 [dm_thin_pool] kernel: [] do_worker+0x51/0x60 [dm_thin_pool] kernel: [] process_one_work+0x183/0x490 kernel: [] worker_thread+0x120/0x3a0 kernel: [] ? manage_workers+0x160/0x160 kernel: [] kthread+0xce/0xf0 kernel: [] ? kthread_freezable_should_stop+0x70/0x70 kernel: [] ret_from_fork+0x7c/0xb0 kernel: [] ? kthread_freezable_should_stop+0x70/0x70 kernel: ---[ end trace 3f00528e08ffa55c ]--- kernel: device-mapper: thin: pool mode is PM_WRITE not PM_READ_ONLY like expected!? dm-thin.c:995 was the WARN_ON_ONCE(get_pool_mode(pool) != PM_READ_ONLY); at the top of handle_unserviceable_bio(). And as the additional debugging I had conveys: the pool mode was _not_ PM_READ_ONLY like expected, it was already PM_WRITE, yet pool->process_bio was still set to process_bio_read_only(). Also, while fixing this up, reduce logging of redundant pool mode transitions by checking new_mode is different from old_mode. Signed-off-by: Mike Snitzer Cc: stable@vger.kernel.org --- Reading git-diff-tree failed