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commit bd293d071ffe65e645b4d8104f9d8fe15ea13862 upstream. When thin-volume is built on loop device, if available memory is low, the following deadlock can be triggered: One process P1 allocates memory with GFP_FS flag, direct alloc fails, memory reclaim invokes memory shrinker in dm_bufio, dm_bufio_shrink_scan() runs, mutex dm_bufio_client->lock is acquired, then P1 waits for dm_buffer IO to complete in __try_evict_buffer(). But this IO may never complete if issued to an underlying loop device that forwards it using direct-IO, which allocates memory using GFP_KERNEL (see: do_blockdev_direct_IO()). If allocation fails, memory reclaim will invoke memory shrinker in dm_bufio, dm_bufio_shrink_scan() will be invoked, and since the mutex is already held by P1 the loop thread will hang, and IO will never complete. Resulting in ABBA deadlock. Cc: stable@vger.kernel.org Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.