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In the common case, req->r_callback is called by handle_reply() on the ceph-msgr worker thread without any locks. If handle_reply() fails, it is called with both osd->lock and osdc->lock. In the map check case, it is called with just osdc->lock but held for write. Finally, if the request is aborted because of -ENOSPC or by ceph_osdc_abort_requests(), it is called directly on the submitter's thread, again with both locks. req->r_callback on the submitter's thread is relatively new (introduced in 4.12) and ripe for deadlocks -- e.g. writeback worker thread waiting on itself: inode_wait_for_writeback+0x26/0x40 evict+0xb5/0x1a0 iput+0x1d2/0x220 ceph_put_wrbuffer_cap_refs+0xe0/0x2c0 [ceph] writepages_finish+0x2d3/0x410 [ceph] __complete_request+0x26/0x60 [libceph] complete_request+0x2e/0x70 [libceph] __submit_request+0x256/0x330 [libceph] submit_request+0x2b/0x30 [libceph] ceph_osdc_start_request+0x25/0x40 [libceph] ceph_writepages_start+0xdfe/0x1320 [ceph] do_writepages+0x1f/0x70 __writeback_single_inode+0x45/0x330 writeback_sb_inodes+0x26a/0x600 __writeback_inodes_wb+0x92/0xc0 wb_writeback+0x274/0x330 wb_workfn+0x2d5/0x3b0 Defer __complete_request() to a workqueue in all failure cases so it's never on the same thread as ceph_osdc_start_request() and always called with no locks held. Link: http://tracker.ceph.com/issues/23978 Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Acked-by: Jeff Layton <jlayton@redhat.com> Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
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.