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BUG: KCSAN: data-race in ucma_create_id / ucma_get_ctx

read to 0xffff888122d52340 of 8 bytes by task 5284 on cpu 1:
 _ucma_find_context drivers/infiniband/core/ucma.c:140 [inline]
 ucma_get_ctx+0x8f/0xf0 drivers/infiniband/core/ucma.c:150
 ucma_resolve_ip+0xb5/0x180 drivers/infiniband/core/ucma.c:704
 ucma_write+0x1fe/0x2a0 drivers/infiniband/core/ucma.c:1684
 __vfs_write+0x67/0xc0 fs/read_write.c:494
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0x17b/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888122d52340 of 8 bytes by task 5279 on cpu 0:
 ucma_create_id+0x1d5/0x380 drivers/infiniband/core/ucma.c:515
 ucma_write+0x1fe/0x2a0 drivers/infiniband/core/ucma.c:1684
 __vfs_write+0x67/0xc0 fs/read_write.c:494
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0x17b/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 5279 Comm: syz-executor.2 Not tainted 5.4.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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