When an ISM device is removed, all its linkgroups are terminated,
i.e. all the corresponding connections are killed.
Connection killing invokes smc_close_active_abort(), which decreases
the sock refcount for certain states to simulate passive closing.
And it cancels the close worker and has to give up the sock lock for
this timeframe. This opens the door for a passive close worker or a
socket close to run in between. In this case smc_close_active_abort() and
passive close worker resp. smc_release() might do a sock_put for passive
closing. This causes:

[ 1323.315943] refcount_t: underflow; use-after-free.
[ 1323.316055] WARNING: CPU: 3 PID: 54469 at lib/refcount.c:28 refcount_warn_saturate+0xe8/0x130
[ 1323.316069] Kernel panic - not syncing: panic_on_warn set ...
[ 1323.316084] CPU: 3 PID: 54469 Comm: uperf Not tainted 5.9.0-20200826.rc2.git0.46328853ed20.300.fc32.s390x+debug #1
[ 1323.316096] Hardware name: IBM 2964 NC9 702 (z/VM 6.4.0)
[ 1323.316108] Call Trace:
[ 1323.316125]  [<00000000c0d4aae8>] show_stack+0x90/0xf8
[ 1323.316143]  [<00000000c15989b0>] dump_stack+0xa8/0xe8
[ 1323.316158]  [<00000000c0d8344e>] panic+0x11e/0x288
[ 1323.316173]  [<00000000c0d83144>] __warn+0xac/0x158
[ 1323.316187]  [<00000000c1597a7a>] report_bug+0xb2/0x130
[ 1323.316201]  [<00000000c0d36424>] monitor_event_exception+0x44/0xc0
[ 1323.316219]  [<00000000c195c716>] pgm_check_handler+0x1da/0x238
[ 1323.316234]  [<00000000c151844c>] refcount_warn_saturate+0xec/0x130
[ 1323.316280] ([<00000000c1518448>] refcount_warn_saturate+0xe8/0x130)
[ 1323.316310]  [<000003ff801f2e2a>] smc_release+0x192/0x1c8 [smc]
[ 1323.316323]  [<00000000c169f1fa>] __sock_release+0x5a/0xe0
[ 1323.316334]  [<00000000c169f2ac>] sock_close+0x2c/0x40
[ 1323.316350]  [<00000000c1086de0>] __fput+0xb8/0x278
[ 1323.316362]  [<00000000c0db1e0e>] task_work_run+0x76/0xb8
[ 1323.316393]  [<00000000c0d8ab84>] do_exit+0x26c/0x520
[ 1323.316408]  [<00000000c0d8af08>] do_group_exit+0x48/0xc0
[ 1323.316421]  [<00000000c0d8afa8>] __s390x_sys_exit_group+0x28/0x38
[ 1323.316433]  [<00000000c195c32c>] system_call+0xe0/0x2b4
[ 1323.316446] 1 lock held by uperf/54469:
[ 1323.316456]  #0: 0000000044125e60 (&sb->s_type->i_mutex_key#9){+.+.}-{3:3}, at: __sock_release+0x44/0xe0

The patch rechecks sock state in smc_close_active_abort() after
smc_close_cancel_work() to avoid duplicate decrease of sock
refcount for the same purpose.

Fixes: 611b63a1 ("net/smc: cancel tx worker in case of socket aborts")
Reviewed-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>