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Flushing the workqueue can cause operations to happen which might call gfs2_log_reserve(), or get stuck waiting for locks taken by such operations. gfs2_log_reserve() can io_schedule(). If this happens, it will never wake because the only thing which can wake it is gfs2_logd() which was already stopped. This causes umount of a gfs2 filesystem to wedge permanently if, for example, the umount immediately follows a large delete operation. When this occured, the following stack trace was obtained from the umount command [<ffffffff81087968>] flush_workqueue+0x1c8/0x520 [<ffffffffa0666e29>] gfs2_make_fs_ro+0x69/0x160 [gfs2] [<ffffffffa0667279>] gfs2_put_super+0xa9/0x1c0 [gfs2] [<ffffffff811b7edf>] generic_shutdown_super+0x6f/0x100 [<ffffffff811b7ff7>] kill_block_super+0x27/0x70 [<ffffffffa0656a71>] gfs2_kill_sb+0x71/0x80 [gfs2] [<ffffffff811b792b>] deactivate_locked_super+0x3b/0x70 [<ffffffff811b79b9>] deactivate_super+0x59/0x60 [<ffffffff811d2998>] cleanup_mnt+0x58/0x80 [<ffffffff811d2a12>] __cleanup_mnt+0x12/0x20 [<ffffffff8108c87d>] task_work_run+0x7d/0xa0 [<ffffffff8106d7d9>] exit_to_usermode_loop+0x73/0x98 [<ffffffff81003961>] syscall_return_slowpath+0x41/0x50 [<ffffffff815a594c>] int_ret_from_sys_call+0x25/0x8f [<ffffffffffffffff>] 0xffffffffffffffff Signed-off-by: Tim Smith <tim.smith@citrix.com> Signed-off-by: Mark Syms <mark.syms@citrix.com> Signed-off-by: Bob Peterson <rpeterso@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.