Re: [PATCH] netfs, ceph: Revert "netfs: Remove deprecated use of PG_private_2 as a second writeback flag"

From: Max Kellermann
Date: Wed Jul 31 2024 - 04:16:42 EST

On Tue, Jul 30, 2024 at 6:28 PM Max Kellermann <max.kellermann@xxxxxxxxx> wrote:
> If I understand this correctly, my other problem (the
> folio_attach_private conflict between netfs and ceph) I posted in
> https://lore.kernel.org/ceph-devel/CAKPOu+8q_1rCnQndOj3KAitNY2scPQFuSS-AxeGru02nP9ZO0w@xxxxxxxxxxxxxx/
> was caused by my (bad) patch after all, wasn't it?

It was not caused by my bad patch. Without my patch, but with your
revert instead I just got a crash (this time, I enabled lots of
debugging options in the kernel, including KASAN) - it's the same
crash as in the post I linked in my previous email:

------------[ cut here ]------------
WARNING: CPU: 13 PID: 3621 at fs/ceph/caps.c:3386
ceph_put_wrbuffer_cap_refs+0x416/0x500
Modules linked in:
CPU: 13 PID: 3621 Comm: rsync Not tainted 6.10.2-cm4all2-vm+ #176
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
RIP: 0010:ceph_put_wrbuffer_cap_refs+0x416/0x500
Code: e8 af 7f 50 01 45 84 ed 75 27 45 8d 74 24 ff e9 cf fd ff ff e8
ab ea 64 ff e9 4c fc ff ff 31 f6 48 89 df e8 3c 86 ff ff eb b5 <0f> 0b
e9 7a ff ff ff 31 f6 48 89 df e8 29 86 ff ff eb cd 0f 0b 48
RSP: 0018:ffff88813c57f868 EFLAGS: 00010286
RAX: dffffc0000000000 RBX: ffff88823dc66588 RCX: 0000000000000000
RDX: 1ffff11047b8cda7 RSI: ffff88823dc66df0 RDI: ffff88823dc66d38
RBP: 0000000000000001 R08: 0000000000000000 R09: fffffbfff5f9a8cd
R10: ffffffffafcd466f R11: 0000000000000001 R12: 0000000000000000
R13: ffffea000947af00 R14: 00000000ffffffff R15: 0000000000000356
FS: 00007f1e82957b80(0000) GS:ffff888a73400000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000559037dacea8 CR3: 000000013f1b2002 CR4: 00000000001706b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
? __warn+0xc8/0x2c0
? ceph_put_wrbuffer_cap_refs+0x416/0x500
? report_bug+0x257/0x2b0
? handle_bug+0x3c/0x70
? exc_invalid_op+0x13/0x40
? asm_exc_invalid_op+0x16/0x20
? ceph_put_wrbuffer_cap_refs+0x416/0x500
? ceph_put_wrbuffer_cap_refs+0x2e/0x500
ceph_invalidate_folio+0x241/0x310
truncate_cleanup_folio+0x277/0x330
truncate_inode_pages_range+0x1b4/0x940
? __pfx_truncate_inode_pages_range+0x10/0x10
? __lock_acquire+0x19f3/0x5c10
? __lock_acquire+0x19f3/0x5c10
? __pfx___lock_acquire+0x10/0x10
? __pfx___lock_acquire+0x10/0x10
? srso_alias_untrain_ret+0x1/0x10
? lock_acquire+0x186/0x490
? find_held_lock+0x2d/0x110
? kvm_sched_clock_read+0xd/0x20
? local_clock_noinstr+0x9/0xb0
? __pfx_lock_release+0x10/0x10
? lockdep_hardirqs_on_prepare+0x275/0x3e0
ceph_evict_inode+0xd5/0x530
evict+0x251/0x560
__dentry_kill+0x17b/0x500
dput+0x393/0x690
__fput+0x40e/0xa60
__x64_sys_close+0x78/0xd0
do_syscall_64+0x82/0x130
? lockdep_hardirqs_on_prepare+0x275/0x3e0
? syscall_exit_to_user_mode+0x9f/0x190
? do_syscall_64+0x8e/0x130
? lockdep_hardirqs_on_prepare+0x275/0x3e0
? lockdep_hardirqs_on_prepare+0x275/0x3e0
? syscall_exit_to_user_mode+0x9f/0x190
? do_syscall_64+0x8e/0x130
? do_syscall_64+0x8e/0x130
? lockdep_hardirqs_on_prepare+0x275/0x3e0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7f1e823178e0
Code: 0d 00 00 00 eb b2 e8 ff f7 01 00 66 2e 0f 1f 84 00 00 00 00 00
0f 1f 44 00 00 80 3d 01 1d 0e 00 00 74 17 b8 03 00 00 00 0f 05 <48> 3d
00 f0 ff ff 77 48 c3 0f 1f 80 00 00 00 00 48 83 ec 18 89 7c
RSP: 002b:00007ffe16c2e108 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 000000000000001e RCX: 00007f1e823178e0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000001
RBP: 00007f1e8219bc08 R08: 0000000000000000 R09: 0000559037df64b0
R10: fe04b91e88691591 R11: 0000000000000202 R12: 0000000000000001
R13: 0000000000000000 R14: 00007ffe16c2e220 R15: 0000000000000001
</TASK>
irq event stamp: 26945
hardirqs last enabled at (26951): [<ffffffffaaac5a99>]
console_unlock+0x189/0x1b0
hardirqs last disabled at (26956): [<ffffffffaaac5a7e>]
console_unlock+0x16e/0x1b0
softirqs last enabled at (26518): [<ffffffffaa962375>] irq_exit_rcu+0x95/0xc0
softirqs last disabled at (26513): [<ffffffffaa962375>] irq_exit_rcu+0x95/0xc0
---[ end trace 0000000000000000 ]---
==================================================================
BUG: KASAN: null-ptr-deref in ceph_put_snap_context+0x18/0x50
Write of size 4 at addr 0000000000000356 by task rsync/3621

CPU: 13 PID: 3621 Comm: rsync Tainted: G W
6.10.2-cm4all2-vm+ #176
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x74/0xd0
kasan_report+0xb9/0xf0
? ceph_put_snap_context+0x18/0x50
kasan_check_range+0xeb/0x1a0
ceph_put_snap_context+0x18/0x50
ceph_invalidate_folio+0x249/0x310
truncate_cleanup_folio+0x277/0x330
truncate_inode_pages_range+0x1b4/0x940
? __pfx_truncate_inode_pages_range+0x10/0x10
? __lock_acquire+0x19f3/0x5c10
? __lock_acquire+0x19f3/0x5c10
? __pfx___lock_acquire+0x10/0x10
? __pfx___lock_acquire+0x10/0x10
? srso_alias_untrain_ret+0x1/0x10
? lock_acquire+0x186/0x490
? find_held_lock+0x2d/0x110
? kvm_sched_clock_read+0xd/0x20
? local_clock_noinstr+0x9/0xb0
? __pfx_lock_release+0x10/0x10
? lockdep_hardirqs_on_prepare+0x275/0x3e0
ceph_evict_inode+0xd5/0x530
evict+0x251/0x560
__dentry_kill+0x17b/0x500
dput+0x393/0x690
__fput+0x40e/0xa60
__x64_sys_close+0x78/0xd0
do_syscall_64+0x82/0x130
? lockdep_hardirqs_on_prepare+0x275/0x3e0
? syscall_exit_to_user_mode+0x9f/0x190
? do_syscall_64+0x8e/0x130
? lockdep_hardirqs_on_prepare+0x275/0x3e0
? lockdep_hardirqs_on_prepare+0x275/0x3e0
? syscall_exit_to_user_mode+0x9f/0x190
? do_syscall_64+0x8e/0x130
? do_syscall_64+0x8e/0x130
? lockdep_hardirqs_on_prepare+0x275/0x3e0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7f1e823178e0
Code: 0d 00 00 00 eb b2 e8 ff f7 01 00 66 2e 0f 1f 84 00 00 00 00 00
0f 1f 44 00 00 80 3d 01 1d 0e 00 00 74 17 b8 03 00 00 00 0f 05 <48> 3d
00 f0 ff ff 77 48 c3 0f 1f 80 00 00 00 00 48 83 ec 18 89 7c
RSP: 002b:00007ffe16c2e108 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 000000000000001e RCX: 00007f1e823178e0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000001
RBP: 00007f1e8219bc08 R08: 0000000000000000 R09: 0000559037df64b0
R10: fe04b91e88691591 R11: 0000000000000202 R12: 0000000000000001
R13: 0000000000000000 R14: 00007ffe16c2e220 R15: 0000000000000001
</TASK>