The patch titled Subject: frontswap: don't call ->init if no ops are registered has been added to the -mm mm-hotfixes-unstable branch. Its filename is frontswap-dont-call-init-if-no-ops-are-registered.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Christoph Hellwig hch@lst.de Subject: frontswap: don't call ->init if no ops are registered Date: Fri, 9 Sep 2022 15:08:29 +0200

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: 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 ---

mm/frontswap.c | 3 +++ 1 file changed, 3 insertions(+)

--- a/mm/frontswap.c~frontswap-dont-call-init-if-no-ops-are-registered +++ a/mm/frontswap.c @@ -125,6 +125,9 @@ void frontswap_init(unsigned type, unsig * p->frontswap set to something valid to work properly. */ frontswap_map_set(sis, map); + + if (!frontswap_enabled()) + return; frontswap_ops->init(type); }

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Patches currently in -mm which might be from hch@lst.de are

frontswap-dont-call-init-if-no-ops-are-registered.patch mm-remove-the-end_write_func-argument-to-__swap_writepage.patch