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Commitc7b7bd0740("bcache: add io_disable to struct cached_dev") tries to stop bcache device by calling bcache_device_stop() when too many I/O errors happened on backing device. But if there is internal I/O happening on cache device (writeback scan, garbage collection, etc), a regular I/O request triggers the internal I/Os may still holds a refcount of dc->count, and the refcount may only be dropped after the internal I/O stopped. By this patch, bch_cached_dev_error() will check if the backing device is attached to a cache set, if yes that CACHE_SET_IO_DISABLE will be set to flags of this cache set. Then internal I/Os on cache device will be rejected and stopped immediately, and the bcache device can be stopped. For people who are not familiar with the interesting refcount dependance, let me explain a bit more how the fix works. Example the writeback thread will scan cache device for dirty data writeback purpose. Before it stopps, it holds a refcount of dc->count. When CACHE_SET_IO_DISABLE bit is set, the internal I/O will stopped and the while-loop in bch_writeback_thread() quits and calls cached_dev_put() to drop dc->count. If this is the last refcount to drop, then cached_dev_detach_finish() will be called. In this call back function, in turn closure_put(dc->disk.cl) is called to drop a refcount of closure dc->disk.cl. If this is the last refcount of this closure to drop, then cached_dev_flush() will be called. Then the cached device is freed. So if CACHE_SET_IO_DISABLE is not set, the bache device can not be stopped until all inernal cache device I/O stopped. For large size cache device, and writeback thread competes locks with gc thread, there might be a quite long time to wait. Fixes:c7b7bd0740("bcache: add io_disable to struct cached_dev") Signed-off-by: Coly Li <colyli@suse.de> Reviewed-by: Hannes Reinecke <hare@suse.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.