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Date:   Mon, 19 Jul 2021 11:42:08 -0700
From:   Roman Gushchin <guro@fb.com>
To:     "Darrick J. Wong" <djwong@kernel.org>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        <linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        Jan Kara <jack@suse.cz>, Dave Chinner <dchinner@redhat.com>,
        Murphy Zhou <jencce.kernel@gmail.com>,
        Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH] writeback, cgroup: do not reparent dax inodes
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References: <20210719171350.3876830-1-guro@fb.com>
 <20210719180441.GH23236@magnolia>
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On Mon, Jul 19, 2021 at 11:04:41AM -0700, Darrick J. Wong wrote:
> On Mon, Jul 19, 2021 at 10:13:50AM -0700, Roman Gushchin wrote:
> > The inode switching code is not suited for dax inodes. An attempt
> > to switch a dax inode to a parent writeback structure (as a part
> > of a writeback cleanup procedure) results in a panic like this:
> > 
> >   [  987.071651] run fstests generic/270 at 2021-07-15 05:54:02
> >   [  988.704940] XFS (pmem0p2): EXPERIMENTAL big timestamp feature in
> >   use.  Use at your own risk!
> >   [  988.746847] XFS (pmem0p2): DAX enabled. Warning: EXPERIMENTAL, use
> >   at your own risk
> >   [  988.786070] XFS (pmem0p2): EXPERIMENTAL inode btree counters
> >   feature in use. Use at your own risk!
> >   [  988.828639] XFS (pmem0p2): Mounting V5 Filesystem
> >   [  988.854019] XFS (pmem0p2): Ending clean mount
> >   [  988.874550] XFS (pmem0p2): Quotacheck needed: Please wait.
> >   [  988.900618] XFS (pmem0p2): Quotacheck: Done.
> >   [  989.090783] XFS (pmem0p2): xlog_verify_grant_tail: space > BBTOB(tail_blocks)
> >   [  989.092751] XFS (pmem0p2): xlog_verify_grant_tail: space > BBTOB(tail_blocks)
> >   [  989.092962] XFS (pmem0p2): xlog_verify_grant_tail: space > BBTOB(tail_blocks)
> >   [ 1010.105586] BUG: unable to handle page fault for address: 0000000005b0f669
> >   [ 1010.141817] #PF: supervisor read access in kernel mode
> >   [ 1010.167824] #PF: error_code(0x0000) - not-present page
> >   [ 1010.191499] PGD 0 P4D 0
> >   [ 1010.203346] Oops: 0000 [#1] SMP PTI
> >   [ 1010.219596] CPU: 13 PID: 10479 Comm: kworker/13:16 Not tainted
> >   5.14.0-rc1-master-8096acd7442e+ #8
> >   [ 1010.260441] Hardware name: HP ProLiant DL360 Gen9/ProLiant DL360
> >   Gen9, BIOS P89 09/13/2016
> >   [ 1010.297792] Workqueue: inode_switch_wbs inode_switch_wbs_work_fn
> >   [ 1010.324832] RIP: 0010:inode_do_switch_wbs+0xaf/0x470
> >   [ 1010.347261] Code: 00 30 0f 85 c1 03 00 00 0f 1f 44 00 00 31 d2 48
> >   c7 c6 ff ff ff ff 48 8d 7c 24 08 e8 eb 49 1a 00 48 85 c0 74 4a bb ff
> >   ff ff ff <48> 8b 50 08 48 8d 4a ff 83 e2 01 48 0f 45 c1 48 8b 00 a8 08
> >   0f 85
> >   [ 1010.434307] RSP: 0018:ffff9c66691abdc8 EFLAGS: 00010002
> >   [ 1010.457795] RAX: 0000000005b0f661 RBX: 00000000ffffffff RCX: ffff89e6a21382b0
> >   [ 1010.489922] RDX: 0000000000000001 RSI: ffff89e350230248 RDI: ffffffffffffffff
> >   [ 1010.522085] RBP: ffff89e681d19400 R08: 0000000000000000 R09: 0000000000000228
> >   [ 1010.554234] R10: ffffffffffffffff R11: ffffffffffffffc0 R12: ffff89e6a2138130
> >   [ 1010.586414] R13: ffff89e316af7400 R14: ffff89e316af6e78 R15: ffff89e6a21382b0
> >   [ 1010.619394] FS:  0000000000000000(0000) GS:ffff89ee5fb40000(0000)
> >   knlGS:0000000000000000
> >   [ 1010.658874] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >   [ 1010.688085] CR2: 0000000005b0f669 CR3: 0000000cb2410004 CR4: 00000000001706e0
> >   [ 1010.722129] Call Trace:
> >   [ 1010.733132]  inode_switch_wbs_work_fn+0xb6/0x2a0
> >   [ 1010.754121]  process_one_work+0x1e6/0x380
> >   [ 1010.772512]  worker_thread+0x53/0x3d0
> >   [ 1010.789221]  ? process_one_work+0x380/0x380
> >   [ 1010.807964]  kthread+0x10f/0x130
> >   [ 1010.822043]  ? set_kthread_struct+0x40/0x40
> >   [ 1010.840818]  ret_from_fork+0x22/0x30
> >   [ 1010.856851] Modules linked in: xt_CHECKSUM xt_MASQUERADE
> >   xt_conntrack ipt_REJECT nf_reject_ipv4 nft_compat nft_chain_nat nf_nat
> >   nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nft_counter nf_tables
> >   nfnetlink bridge stp llc rfkill sunrpc intel_rapl_msr
> >   intel_rapl_common sb_edac x86_pkg_temp_thermal intel_powerclamp
> >   coretemp kvm_intel ipmi_ssif kvm mgag200 i2c_algo_bit iTCO_wdt
> >   irqbypass drm_kms_helper iTCO_vendor_support acpi_ipmi rapl
> >   syscopyarea sysfillrect intel_cstate ipmi_si sysimgblt ioatdma
> >   dax_pmem_compat fb_sys_fops ipmi_devintf device_dax i2c_i801 pcspkr
> >   intel_uncore hpilo nd_pmem cec dax_pmem_core dca i2c_smbus acpi_tad
> >   lpc_ich ipmi_msghandler acpi_power_meter drm fuse xfs libcrc32c sd_mod
> >   t10_pi crct10dif_pclmul crc32_pclmul crc32c_intel tg3
> >   ghash_clmulni_intel serio_raw hpsa hpwdt scsi_transport_sas wmi
> >   dm_mirror dm_region_hash dm_log dm_mod
> >   [ 1011.200864] CR2: 0000000005b0f669
> >   [ 1011.215700] ---[ end trace ed2105faff8384f3 ]---
> >   [ 1011.241727] RIP: 0010:inode_do_switch_wbs+0xaf/0x470
> >   [ 1011.264306] Code: 00 30 0f 85 c1 03 00 00 0f 1f 44 00 00 31 d2 48
> >   c7 c6 ff ff ff ff 48 8d 7c 24 08 e8 eb 49 1a 00 48 85 c0 74 4a bb ff
> >   ff ff ff <48> 8b 50 08 48 8d 4a ff 83 e2 01 48 0f 45 c1 48 8b 00 a8 08
> >   0f 85
> >   [ 1011.348821] RSP: 0018:ffff9c66691abdc8 EFLAGS: 00010002
> >   [ 1011.372734] RAX: 0000000005b0f661 RBX: 00000000ffffffff RCX: ffff89e6a21382b0
> >   [ 1011.405826] RDX: 0000000000000001 RSI: ffff89e350230248 RDI: ffffffffffffffff
> >   [ 1011.437852] RBP: ffff89e681d19400 R08: 0000000000000000 R09: 0000000000000228
> >   [ 1011.469926] R10: ffffffffffffffff R11: ffffffffffffffc0 R12: ffff89e6a2138130
> >   [ 1011.502179] R13: ffff89e316af7400 R14: ffff89e316af6e78 R15: ffff89e6a21382b0
> >   [ 1011.534233] FS:  0000000000000000(0000) GS:ffff89ee5fb40000(0000)
> >   knlGS:0000000000000000
> >   [ 1011.571247] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >   [ 1011.597063] CR2: 0000000005b0f669 CR3: 0000000cb2410004 CR4: 00000000001706e0
> >   [ 1011.629160] Kernel panic - not syncing: Fatal exception
> >   [ 1011.653802] Kernel Offset: 0x15200000 from 0xffffffff81000000
> >   (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
> >   [ 1011.713723] ---[ end Kernel panic - not syncing: Fatal exception ]---
> > 
> > The crash happens on an attempt to iterate over attached pagecache
> > pages and check the dirty flag: a dax inode's xarray contains pfn's
> > instead of generic struct page pointers.
> > 
> > Fix the problem by bailing out (with the false return value) of
> > inode_prepare_sbs_switch() if a dax inode is passed.
> > 
> > Fixes: c22d70a162d3 ("writeback, cgroup: release dying cgwbs by switching attached inodes")
> > Signed-off-by: Roman Gushchin <guro@fb.com>
> > Reported-by: Murphy Zhou <jencce.kernel@gmail.com>
> > Reported-by: Darrick J. Wong <djwong@kernel.org>
> > Tested-by: Murphy Zhou <jencce.kernel@gmail.com>
> > Cc: Matthew Wilcox <willy@infradead.org>
> 
> Seems to fix the problem here too, so:
> Tested-by: Darrick J. Wong <djwong@kernel.org>

Thank you!