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We should remove O_NONBLOCK flag when calling sock->ops->connect() in sctp_connect_to_sock() function. Why? 1. up to now, sctp socket connect() function ignores the flag argument, that means O_NONBLOCK flag does not take effect, then we should remove it to avoid the confusion (but is not urgent). 2. for the future, there will be a patch to fix this problem, then the flag argument will take effect, the patch has been queued at https://git.kernel.o rg/pub/scm/linux/kernel/git/davem/net.git/commit/net/sctp?id=644fbdeacf1d3ed d366e44b8ba214de9d1dd66a9. But, the O_NONBLOCK flag will make sock->ops->connect() directly return without any wait time, then the connection will not be established, DLM kernel module will call sock->ops->connect() again and again, the bad results are, CPU usage is almost 100%, even trigger soft_lockup problem if the related configurations are enabled, DLM kernel module also prints lots of messages like, [Fri Apr 27 11:23:43 2018] dlm: connecting to 172167592 [Fri Apr 27 11:23:43 2018] dlm: connecting to 172167592 [Fri Apr 27 11:23:43 2018] dlm: connecting to 172167592 [Fri Apr 27 11:23:43 2018] dlm: connecting to 172167592 The upper application (e.g. ocfs2 mount command) is hanged at new_lockspace(), the whole backtrace is as below, tb0307-nd2:~ # cat /proc/2935/stack [<0>] new_lockspace+0x957/0xac0 [dlm] [<0>] dlm_new_lockspace+0xae/0x140 [dlm] [<0>] user_cluster_connect+0xc3/0x3a0 [ocfs2_stack_user] [<0>] ocfs2_cluster_connect+0x144/0x220 [ocfs2_stackglue] [<0>] ocfs2_dlm_init+0x215/0x440 [ocfs2] [<0>] ocfs2_fill_super+0xcb0/0x1290 [ocfs2] [<0>] mount_bdev+0x173/0x1b0 [<0>] mount_fs+0x35/0x150 [<0>] vfs_kern_mount.part.23+0x54/0x100 [<0>] do_mount+0x59a/0xc40 [<0>] SyS_mount+0x80/0xd0 [<0>] do_syscall_64+0x76/0x140 [<0>] entry_SYSCALL_64_after_hwframe+0x42/0xb7 [<0>] 0xffffffffffffffff So, I think we should remove O_NONBLOCK flag here, since DLM kernel module can not handle non-block sockect in connect() properly. Signed-off-by: Gang He <ghe@suse.com> Signed-off-by: David Teigland <teigland@redhat.com> |
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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.