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549af00833
When rdmacm module is not loaded, and when netlink message is received to
get char device info, it results into a deadlock due to recursive locking
of rdma_nl_mutex with the below call sequence.
[..]
rdma_nl_rcv()
mutex_lock()
[..]
rdma_nl_rcv_msg()
ib_get_client_nl_info()
request_module()
iw_cm_init()
rdma_nl_register()
mutex_lock(); <- Deadlock, acquiring mutex again
Due to above call sequence, following call trace and deadlock is observed.
kernel: __mutex_lock+0x35e/0x860
kernel: ? __mutex_lock+0x129/0x860
kernel: ? rdma_nl_register+0x1a/0x90 [ib_core]
kernel: rdma_nl_register+0x1a/0x90 [ib_core]
kernel: ? 0xffffffffc029b000
kernel: iw_cm_init+0x34/0x1000 [iw_cm]
kernel: do_one_initcall+0x67/0x2d4
kernel: ? kmem_cache_alloc_trace+0x1ec/0x2a0
kernel: do_init_module+0x5a/0x223
kernel: load_module+0x1998/0x1e10
kernel: ? __symbol_put+0x60/0x60
kernel: __do_sys_finit_module+0x94/0xe0
kernel: do_syscall_64+0x5a/0x270
kernel: entry_SYSCALL_64_after_hwframe+0x49/0xbe
process stack trace:
[<0>] __request_module+0x1c9/0x460
[<0>] ib_get_client_nl_info+0x5e/0xb0 [ib_core]
[<0>] nldev_get_chardev+0x1ac/0x320 [ib_core]
[<0>] rdma_nl_rcv_msg+0xeb/0x1d0 [ib_core]
[<0>] rdma_nl_rcv+0xcd/0x120 [ib_core]
[<0>] netlink_unicast+0x179/0x220
[<0>] netlink_sendmsg+0x2f6/0x3f0
[<0>] sock_sendmsg+0x30/0x40
[<0>] ___sys_sendmsg+0x27a/0x290
[<0>] __sys_sendmsg+0x58/0xa0
[<0>] do_syscall_64+0x5a/0x270
[<0>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
To overcome this deadlock and to allow multiple netlink messages to
progress in parallel, following scheme is implemented.
1. Split the lock protecting the cb_table into a per-index lock, and make
it a rwlock. This lock is used to ensure no callbacks are running after
unregistration returns. Since a module will not be registered once it
is already running callbacks, this avoids the deadlock.
2. Use smp_store_release() to update the cb_table during registration so
that no lock is required. This avoids lockdep problems with thinking
all the rwsems are the same lock class.
Fixes:
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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.
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.