rds: do not call ->conn_alloc with GFP_KERNEL

rds: do not call ->conn_alloc with GFP_KERNEL

Commit ebeeb1ad9b8a ("rds: tcp: use rds_destroy_pending() to synchronize
netns/module teardown and rds connection/workq management")
adds an rcu read critical section to __rd_conn_create. The
memory allocations in that critcal section need to use
GFP_ATOMIC to avoid sleeping.

This patch was verified with syzkaller reproducer.

Reported-by: [email protected]
Fixes: ebeeb1ad9b8a ("rds: tcp: use rds_destroy_pending() to synchronize
       netns/module teardown and rds connection/workq management")
Signed-off-by: Sowmini Varadhan <[email protected]>
Acked-by: Santosh Shilimkar <[email protected]>
Signed-off-by: David S. Miller <[email protected]>