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Parav Pandit authored
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: 0e2d00eb ("RDMA: Add NLDEV_GET_CHARDEV to allow char dev discovery and autoload") Link: https://lore.kernel.org/r/20191015080733.18625-1-leon@kernel.orgSigned-off-by:
Parav Pandit <parav@mellanox.com> Signed-off-by:
Leon Romanovsky <leonro@mellanox.com> Signed-off-by:
Jason Gunthorpe <jgg@mellanox.com>
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