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BUG: KCSAN: data-race in ucma_create_id / ucma_get_ctx

write to 0xffff888103048100 of 8 bytes by task 1763 on cpu 0:
 ucma_create_id+0x2bf/0x2d0 drivers/infiniband/core/ucma.c:522
 ucma_write+0x229/0x250 drivers/infiniband/core/ucma.c:1764
 vfs_write+0x1d6/0x690 fs/read_write.c:576
 ksys_write+0xce/0x180 fs/read_write.c:631
 __do_sys_write fs/read_write.c:643 [inline]
 __se_sys_write fs/read_write.c:640 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:640
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888103048100 of 8 bytes by task 1768 on cpu 1:
 _ucma_find_context drivers/infiniband/core/ucma.c:142 [inline]
 ucma_get_ctx+0x7b/0x140 drivers/infiniband/core/ucma.c:152
 ucma_resolve_ip+0xd3/0x1b0 drivers/infiniband/core/ucma.c:717
 ucma_write+0x229/0x250 drivers/infiniband/core/ucma.c:1764
 vfs_write+0x1d6/0x690 fs/read_write.c:576
 ksys_write+0xce/0x180 fs/read_write.c:631
 __do_sys_write fs/read_write.c:643 [inline]
 __se_sys_write fs/read_write.c:640 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:640
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1768 Comm: syz-executor.2 Not tainted 5.8.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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