drivers: net: cpsw: fix crash while accessing second slave ethernet interface

drivers: net: cpsw: fix crash while accessing second slave ethernet interface

When cpsw's number of slave is set to 1 in device tree and while
accessing second slave ndev and priv in cpsw_tx_interrupt(),
there is a kernel crash. This is due to cpsw_get_slave_priv()
not verifying number of slaves while retriving netdev priv and
returns a invalid memory region. Fixing the issue by introducing
number of slave check in cpsw_get_slave_priv() and
cpsw_get_slave_ndev().

[   15.879589] Unable to handle kernel paging request at virtual address 0f0e142c
[   15.888540] pgd = ed374000
[   15.891359] [0f0e142c] *pgd=00000000
[   15.895105] Internal error: Oops: 5 [#1] SMP ARM
[   15.899936] Modules linked in:
[   15.903139] CPU: 0 PID: 593 Comm: udhcpc Tainted: G        W       4.1.0-12205-gfda8b18-dirty #10
[   15.912386] Hardware name: Generic AM43 (Flattened Device Tree)
[   15.918557] task: ed2a2e00 ti: ed3fe000 task.ti: ed3fe000
[   15.924187] PC is at cpsw_tx_interrupt+0x30/0x44
[   15.929008] LR is at _raw_spin_unlock_irqrestore+0x40/0x44
[   15.934726] pc : [<c048b9cc>]    lr : [<c05ef4f4>]    psr: 20000193
[   15.934726] sp : ed3ffc08  ip : ed2a2e40  fp : 00000000
[   15.946685] r10: c0969ce8  r9 : c0969cfc  r8 : 00000000
[   15.952129] r7 : 000000c6  r6 : ee54ab00  r5 : ee169c64  r4 : ee534e00
[   15.958932] r3 : 0f0e0d0c  r2 : 00000000  r1 : ed3ffbc0  r0 : 00000001
[   15.965735] Flags: nzCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment user
[   15.973261] Control: 10c5387d  Table: ad374059  DAC: 00000015
[   15.979246] Process udhcpc (pid: 593, stack limit = 0xed3fe218)
[   15.985414] Stack: (0xed3ffc08 to 0xed400000)
[   15.989954] fc00:                   ee54ab00 c009928c c0a9e648 60000193 000032e4 ee169c00
[   15.998478] fc20: ee169c64 ee169c00 ee169c64 ee54ab00 00000001 00000001 ee67e268 ee008800
[   16.006995] fc40: ee534800 c009946c ee169c00 ee169c64 c08bd660 c009c370 c009c2a4 000000c6
[   16.015513] fc60: c08b75c4 c08b0854 00000000 c0098b3c 000000c6 c0098c50 ed3ffcb0 0000003a
[   16.024033] fc80: ed3ffcb0 fa24010c c08b7800 fa240100 ee7e9880 c00094c4 c05ef4e8 60000013
[   16.032556] fca0: ffffffff ed3ffce4 ee7e9880 c05ef964 00000001 ed2a33d8 00000000 ed2a2e00
[   16.041080] fcc0: 60000013 ee536bf8 60000013 ee51b800 ee7e9880 ee67e268 ee7e9880 ee534800
[   16.049603] fce0: c0ad0768 ed3ffcf8 c008e910 c05ef4e8 60000013 ffffffff 00000001 00000001
[   16.058121] fd00: ee536bf8 c0487a04 00000000 00000000 ee534800 00000000 00000156 c048c990
[   16.066645] fd20: 00000000 00000000 c0969f40 00000000 00000000 c05000e8 00000001 00000000
[   16.075167] fd40: 00000000 c051eefc 00000000 ee67e268 00000000 00000000 ee51b800 ed3ffd9c
[   16.083690] fd60: 00000000 ee67e200 ee51b800 ee7e9880 ee67e268 00000000 00000000 ee67e200
[   16.092211] fd80: ee51b800 ee7e9880 ee67e268 ee534800 ee67e200 c051eedc ee67e268 00000010
[   16.100727] fda0: 00000000 00000000 ee7e9880 ee534800 00000000 ee67e268 ee51b800 c05006fc
[   16.109247] fdc0: ee67e268 00000001 c0500488 00000156 ee7e9880 00000000 ed3fe000 fffffff4
[   16.117771] fde0: ed3fff1c ee7e9880 ee534800 00000148 00000000 ed1f8340 00000000 00000000
[   16.126289] fe00: 00000000 c05a9054 00000000 00000000 00000156 c0ab62a8 00000010 ed3e7000
[   16.134812] fe20: 00000000 00000008 edcfb700 ed3fff1c c0fb5f94 ed2a2e00 c0fb5f64 000005d8
[   16.143336] fe40: c0a9b3b8 00000000 ed3e7070 00000000 00000000 00000000 00009f40 00000000
[   16.151858] fe60: 00000000 00020022 00110008 00000000 00000000 43004400 00000000 ffffffff
[   16.160374] fe80: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[   16.168898] fea0: edcfb700 bee5f380 00000014 00000000 ed3fe000 00000000 00004400 c04e2b64
[   16.177415] fec0: 00000002 c04e3b00 ed3ffeec 00000001 0000011a 00000000 00000000 bee5f394
[   16.185937] fee0: 00000148 ed3fff10 00000014 00000001 00000000 00000000 ed3ffee4 00000000
[   16.194459] ff00: 00000000 00000000 00000000 c04e3664 00080011 00000002 06000000 ffffffff
[   16.202980] ff20: 0000ffff ffffffff 0000ffff c008dd54 ee5a6f08 ee636e80 c096972d c0089c14
[   16.211499] ff40: 00000000 60000013 ee5a6f40 60000013 00000000 ee5a6f40 00000002 00000006
[   16.220023] ff60: 00000000 edcfb700 00000001 ed2a2e00 c000f60c 00000001 0000011a c008ea34
[   16.228540] ff80: 00000006 00000000 bee5f380 00000014 bee5f380 00000014 bee5f380 00000122
[   16.237059] ffa0: c000f7c4 c000f5e0 bee5f380 00000014 00000006 bee5f394 00000148 00000000
[   16.245581] ffc0: bee5f380 00000014 bee5f380 00000122 fffffd6e 00004300 00004800 00004400
[   16.254104] ffe0: bee5f378 bee5f36c 000307ec b6f39044 40000010 00000006 ed36fa40 00000000
[   16.262642] [<c048b9cc>] (cpsw_tx_interrupt) from [<c009928c>] (handle_irq_event_percpu+0x64/0x204)
[   16.272076] [<c009928c>] (handle_irq_event_percpu) from [<c009946c>] (handle_irq_event+0x40/0x64)
[   16.281330] [<c009946c>] (handle_irq_event) from [<c009c370>] (handle_fasteoi_irq+0xcc/0x1a8)
[   16.290220] [<c009c370>] (handle_fasteoi_irq) from [<c0098b3c>] (generic_handle_irq+0x20/0x30)
[   16.299197] [<c0098b3c>] (generic_handle_irq) from [<c0098c50>] (__handle_domain_irq+0x64/0xdc)
[   16.308273] [<c0098c50>] (__handle_domain_irq) from [<c00094c4>] (gic_handle_irq+0x20/0x60)
[   16.316987] [<c00094c4>] (gic_handle_irq) from [<c05ef964>] (__irq_svc+0x44/0x5c)
[   16.324779] Exception stack(0xed3ffcb0 to 0xed3ffcf8)
[   16.330044] fca0:                                     00000001 ed2a33d8 00000000 ed2a2e00
[   16.338567] fcc0: 60000013 ee536bf8 60000013 ee51b800 ee7e9880 ee67e268 ee7e9880 ee534800
[   16.347090] fce0: c0ad0768 ed3ffcf8 c008e910 c05ef4e8 60000013 ffffffff
[   16.353987] [<c05ef964>] (__irq_svc) from [<c05ef4e8>] (_raw_spin_unlock_irqrestore+0x34/0x44)
[   16.362973] [<c05ef4e8>] (_raw_spin_unlock_irqrestore) from [<c0487a04>] (cpdma_check_free_tx_desc+0x60/0x6c)
[   16.373311] [<c0487a04>] (cpdma_check_free_tx_desc) from [<c048c990>] (cpsw_ndo_start_xmit+0xb4/0x1ac)
[   16.383017] [<c048c990>] (cpsw_ndo_start_xmit) from [<c05000e8>] (dev_hard_start_xmit+0x2a4/0x4c0)
[   16.392364] [<c05000e8>] (dev_hard_start_xmit) from [<c051eedc>] (sch_direct_xmit+0xf4/0x210)
[   16.401246] [<c051eedc>] (sch_direct_xmit) from [<c05006fc>] (__dev_queue_xmit+0x2ac/0x7bc)
[   16.409960] [<c05006fc>] (__dev_queue_xmit) from [<c05a9054>] (packet_sendmsg+0xc68/0xeb4)
[   16.418585] [<c05a9054>] (packet_sendmsg) from [<c04e2b64>] (sock_sendmsg+0x14/0x24)
[   16.426663] [<c04e2b64>] (sock_sendmsg) from [<c04e3b00>] (SyS_sendto+0xb4/0xe0)
[   16.434377] [<c04e3b00>] (SyS_sendto) from [<c000f5e0>] (ret_fast_syscall+0x0/0x54)
[   16.442360] Code: e5943118 e593303c e3530000 0a000002 (e5930720)
[   16.448716] ---[ end trace a68159f094d85ba6 ]---
[   16.453526] Kernel panic - not syncing: Fatal exception in interrupt
[   16.460149] ---[ end Kernel panic - not syncing: Fatal exception in interrupt

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Cc: <stable@vger.kernel.org> # v3.8+
Signed-off-by: David S. Miller <davem@davemloft.net>