frontswap: don't call ->init if no ops are registered
If no frontswap module (i.e. zswap) was registered, frontswap_ops will be
NULL. In such situation, swapon crashes with the following stack trace:
Unable to handle kernel access to user memory outside uaccess routines at virtual address
0000000000000000
Mem abort info:
ESR = 0x0000000096000004
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x04: level 0 translation fault
Data abort info:
ISV = 0, ISS = 0x00000004
CM = 0, WnR = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=
00000020a4fab000
[
0000000000000000] pgd=
0000000000000000, p4d=
0000000000000000
Internal error: Oops:
96000004 [#1] SMP
Modules linked in: zram fsl_dpaa2_eth pcs_lynx phylink ahci_qoriq crct10dif_ce ghash_ce sbsa_gwdt fsl_mc_dpio nvme lm90 nvme_core at803x xhci_plat_hcd rtc_fsl_ftm_alarm xgmac_mdio ahci_platform i2c_imx ip6_tables ip_tables fuse
Unloaded tainted modules: cppc_cpufreq():1
CPU: 10 PID: 761 Comm: swapon Not tainted
6.0.0-rc2-00454-g22100432cf14 #1
Hardware name: SolidRun Ltd. SolidRun CEX7 Platform, BIOS EDK II Jun 21 2022
pstate:
00400005 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : frontswap_init+0x38/0x60
lr : __do_sys_swapon+0x8a8/0x9f4
sp :
ffff80000969bcf0
x29:
ffff80000969bcf0 x28:
ffff37bee0d8fc00 x27:
ffff80000a7f5000
x26:
fffffcdefb971e80 x25:
ffffaba797453b90 x24:
0000000000000064
x23:
ffff37c1f209d1a8 x22:
ffff37bee880e000 x21:
ffffaba797748560
x20:
ffff37bee0d8fce4 x19:
ffffaba797748488 x18:
0000000000000014
x17:
0000000030ec029a x16:
ffffaba795a479b0 x15:
0000000000000000
x14:
0000000000000000 x13:
0000000000000030 x12:
0000000000000001
x11:
ffff37c63c0aba18 x10:
0000000000000000 x9 :
ffffaba7956b8c88
x8 :
ffff80000969bcd0 x7 :
0000000000000000 x6 :
0000000000000000
x5 :
0000000000000001 x4 :
0000000000000000 x3 :
ffffaba79730f000
x2 :
ffff37bee0d8fc00 x1 :
0000000000000000 x0 :
0000000000000000
Call trace:
frontswap_init+0x38/0x60
__do_sys_swapon+0x8a8/0x9f4
__arm64_sys_swapon+0x28/0x3c
invoke_syscall+0x78/0x100
el0_svc_common.constprop.0+0xd4/0xf4
do_el0_svc+0x38/0x4c
el0_svc+0x34/0x10c
el0t_64_sync_handler+0x11c/0x150
el0t_64_sync+0x190/0x194
Code:
d000e283 910003fd f9006c41 f946d461 (
f9400021)
---[ end trace
0000000000000000 ]---
Link: https://lkml.kernel.org/r/20220909130829.3262926-1-hch@lst.de
Fixes: 1da0d94a3ec8 ("frontswap: remove support for multiple ops")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>