Hi It's hard to say what causes this. Perhaps dm-crypt exhausts all the higher-order pages and some subsystem stalls because of it. In drivers/md/dm-crypt.c in function crypt_alloc_buffer there is "unsigned int order = MAX_ORDER - 1" What happens if you set the "order" variable to some small value, like 1, 2 or 3. Does the problem go away? Could you find a threshold value (something between 0 and MAX_ORDER-1) where the bug starts to appear? What happens if you replace "pages = alloc_pages(gfp_mask" with "pages = alloc_pages((gfp_mask & ~__GFP_KSWAPD_RECLAIM)" ? Does the bug go away? Mikulas On Sat, 21 Oct 2023, Marek Marczykowski-Górecki wrote: > Hi, > > Since updating from 6.4.13 to 6.5.5 occasionally I hit a storage > subsystem freeze - any I/O ends up frozen. I'm not sure what exactly > triggers the issue, but often it happens when doing some LVM operations > (lvremove, lvrename etc) on a dm-thin volume together with bulk data > copy to/from another LVM thin volume with ext4 fs. > > The storage stack I use is: > nvme -> dm-crypt (LUKS) -> dm-thin (LVM thin pool) -> ext4 > > And this whole thing running in a (PV) dom0 under Xen, on Qubes OS 4.2 to be > specific. > > I can reproduce the issue on at least 3 different machines. I did tried > also 6.5.6 and the issue is still there. I haven't checked newer > versions, but briefly reviewed git log and haven't found anything > suggesting a fix to similar issue. > > I managed to bisect it down to this commit: > > commit 5054e778fcd9cd29ddaa8109077cd235527e4f94 > Author: Mikulas Patocka <mpatocka@xxxxxxxxxx> > Date: Mon May 1 09:19:17 2023 -0400 > > dm crypt: allocate compound pages if possible > > It was reported that allocating pages for the write buffer in dm-crypt > causes measurable overhead [1]. > > Change dm-crypt to allocate compound pages if they are available. If > not, fall back to the mempool. > > [1] https://listman.redhat.com/archives/dm-devel/2023-February/053284.html > > Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx> > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> > Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> > > TBH, I'm not sure if the bug is in this commit, or maybe in some > functions it uses (I don't see dm-crypt functions directly involved in > the stack traces I collected). But reverting this commit on top of 6.5.6 > seems to fix the issue. > > I tried also CONFIG_PROVE_LOCKING, but it didn't show any issue. > > I managed to collect "blocked tasks" dump via sysrq below. Few more can > be found at https://github.com/QubesOS/qubes-issues/issues/8575 > > [ 4246.558313] sysrq: Show Blocked State > [ 4246.558388] task:journal-offline state:D stack:0 pid:8098 ppid:1 flags:0x00000002 > [ 4246.558407] Call Trace: > [ 4246.558414] <TASK> > [ 4246.558422] __schedule+0x23d/0x670 > [ 4246.558440] schedule+0x5e/0xd0 > [ 4246.558450] io_schedule+0x46/0x70 > [ 4246.558461] folio_wait_bit_common+0x13d/0x350 > [ 4246.558475] ? __pfx_wake_page_function+0x10/0x10 > [ 4246.558488] folio_wait_writeback+0x2c/0x90 > [ 4246.558498] mpage_prepare_extent_to_map+0x15c/0x4d0 > [ 4246.558512] ext4_do_writepages+0x25f/0x770 > [ 4246.558523] ext4_writepages+0xad/0x180 > [ 4246.558533] do_writepages+0xcf/0x1e0 > [ 4246.558543] ? __seccomp_filter+0x32a/0x4f0 > [ 4246.558554] filemap_fdatawrite_wbc+0x63/0x90 > [ 4246.558567] __filemap_fdatawrite_range+0x5c/0x80 > [ 4246.558578] file_write_and_wait_range+0x4a/0xb0 > [ 4246.558588] ext4_sync_file+0x88/0x380 > [ 4246.558598] __x64_sys_fsync+0x3b/0x70 > [ 4246.558609] do_syscall_64+0x5c/0x90 > [ 4246.558621] ? exit_to_user_mode_prepare+0xb2/0xd0 > [ 4246.558632] entry_SYSCALL_64_after_hwframe+0x6e/0xd8 > [ 4246.558644] RIP: 0033:0x7710cf124d0a > [ 4246.558654] RSP: 002b:00007710ccdfda40 EFLAGS: 00000293 ORIG_RAX: 000000000000004a > [ 4246.558668] RAX: ffffffffffffffda RBX: 000064bb92f67e60 RCX: 00007710cf124d0a > [ 4246.558679] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000028 > [ 4246.558691] RBP: 000064bb92f72670 R08: 0000000000000000 R09: 00007710ccdfe6c0 > [ 4246.558702] R10: 00007710cf0adfee R11: 0000000000000293 R12: 000064bb92505940 > [ 4246.558713] R13: 0000000000000002 R14: 00007ffc05649500 R15: 00007710cc5fe000 > [ 4246.558728] </TASK> > [ 4246.558836] task:lvm state:D stack:0 pid:7835 ppid:5665 flags:0x00004006 > [ 4246.558852] Call Trace: > [ 4246.558857] <TASK> > [ 4246.558863] __schedule+0x23d/0x670 > [ 4246.558874] schedule+0x5e/0xd0 > [ 4246.558884] io_schedule+0x46/0x70 > [ 4246.558894] dm_wait_for_bios_completion+0xfc/0x110 > [ 4246.558909] ? __pfx_autoremove_wake_function+0x10/0x10 > [ 4246.558922] __dm_suspend+0x7e/0x1b0 > [ 4246.558932] dm_internal_suspend_noflush+0x5c/0x80 > [ 4246.558946] pool_presuspend+0xcc/0x130 [dm_thin_pool] > [ 4246.558968] dm_table_presuspend_targets+0x3f/0x60 > [ 4246.558980] __dm_suspend+0x41/0x1b0 > [ 4246.558991] dm_suspend+0xc0/0xe0 > [ 4246.559001] dev_suspend+0xa5/0xd0 > [ 4246.559011] ctl_ioctl+0x26e/0x350 > [ 4246.559020] ? __pfx_dev_suspend+0x10/0x10 > [ 4246.559032] dm_ctl_ioctl+0xe/0x20 > [ 4246.559041] __x64_sys_ioctl+0x94/0xd0 > [ 4246.559052] do_syscall_64+0x5c/0x90 > [ 4246.559062] ? do_syscall_64+0x6b/0x90 > [ 4246.559072] ? do_syscall_64+0x6b/0x90 > [ 4246.559081] ? xen_pv_evtchn_do_upcall+0x54/0xb0 > [ 4246.559093] entry_SYSCALL_64_after_hwframe+0x6e/0xd8 > [ 4246.559104] RIP: 0033:0x7f1cb77cfe0f > [ 4246.559112] RSP: 002b:00007fff870f2560 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 > [ 4246.559141] RAX: ffffffffffffffda RBX: 00005b8d13c16580 RCX: 00007f1cb77cfe0f > [ 4246.559152] RDX: 00005b8d144a2180 RSI: 00000000c138fd06 RDI: 0000000000000003 > [ 4246.559164] RBP: 00005b8d144a2180 R08: 00005b8d132b1190 R09: 00007fff870f2420 > [ 4246.559175] R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000c > [ 4246.559186] R13: 00005b8d132aacf0 R14: 00005b8d1324414d R15: 00005b8d144a21b0 > [ 4246.559199] </TASK> > [ 4246.559207] task:kworker/u8:3 state:D stack:0 pid:8033 ppid:2 flags:0x00004000 > [ 4246.559222] Workqueue: writeback wb_workfn (flush-253:4) > [ 4246.559238] Call Trace: > [ 4246.559244] <TASK> > [ 4246.559249] __schedule+0x23d/0x670 > [ 4246.559260] schedule+0x5e/0xd0 > [ 4246.559270] io_schedule+0x46/0x70 > [ 4246.559280] folio_wait_bit_common+0x13d/0x350 > [ 4246.559290] ? __pfx_wake_page_function+0x10/0x10 > [ 4246.559302] mpage_prepare_extent_to_map+0x309/0x4d0 > [ 4246.559314] ext4_do_writepages+0x25f/0x770 > [ 4246.559324] ext4_writepages+0xad/0x180 > [ 4246.559334] do_writepages+0xcf/0x1e0 > [ 4246.559344] ? find_busiest_group+0x42/0x1a0 > [ 4246.559354] __writeback_single_inode+0x3d/0x280 > [ 4246.559368] writeback_sb_inodes+0x1ed/0x4a0 > [ 4246.559381] __writeback_inodes_wb+0x4c/0xf0 > [ 4246.559393] wb_writeback+0x298/0x310 > [ 4246.559403] wb_do_writeback+0x230/0x2b0 > [ 4246.559414] wb_workfn+0x5f/0x260 > [ 4246.559424] ? _raw_spin_unlock+0xe/0x30 > [ 4246.559434] ? finish_task_switch.isra.0+0x95/0x2b0 > [ 4246.559447] ? __schedule+0x245/0x670 > [ 4246.559457] process_one_work+0x1df/0x3e0 > [ 4246.559466] worker_thread+0x51/0x390 > [ 4246.559475] ? __pfx_worker_thread+0x10/0x10 > [ 4246.559484] kthread+0xe5/0x120 > [ 4246.559495] ? __pfx_kthread+0x10/0x10 > [ 4246.559504] ret_from_fork+0x31/0x50 > [ 4246.559514] ? __pfx_kthread+0x10/0x10 > [ 4246.559523] ret_from_fork_asm+0x1b/0x30 > [ 4246.559536] </TASK> > > -- > Best Regards, > Marek Marczykowski-Górecki > Invisible Things Lab >
