On 18. 07. 20, 19:14, Oleg Nesterov wrote: > On 07/18, Jiri Slaby wrote: >> >> On 17. 07. 20, 14:40, Oleg Nesterov wrote: >>> >>> please see the updated patch below, lets check ptrace_unfreeze() too. >> >> Sure, dmesg attached. > > Thanks a lot! > > But I am totally confused... > >> [ 94.513944] ------------[ cut here ]------------ >> [ 94.513985] do not call blocking ops when !TASK_RUNNING; state=8 set at >> [<000000002fe279e9>] ptrace_check_attach+0xbf/0x110 > > OK, so the ptracer has already did the TASK_TRACED -> __TASK_TRACED change in > ptrace_freeze_traced(), > >> [ 94.514019] WARNING: CPU: 16 PID: 34171 at kernel/sched/core.c:6881 >> __might_sleep+0x6c/0x70 >> [ 94.514020] Modules linked in: ata_generic(E) pata_acpi(E) >> crc32_pclmul(E) qemu_fw_cfg(E) ata_piix(E) e1000(E) nls_iso8859_1(E) >> nls_cp437(E) vfat(E) fat(E) virtio_blk(E) virtio_mmio(E) xfs(E) btrfs(E) >> blake2b_generic(E) xor(E) raid6_pq(E) libcrc32c(E) crc32c_intel(E) >> reiserfs(E) squashfs(E) fuse(E) dm_snapshot(E) dm_bufio(E) dm_crypt(E) >> dm_mod(E) binfmt_misc(E) loop(E) sg(E) virtio_rng(E) >> [ 94.514082] CPU: 16 PID: 34171 Comm: strace Tainted: G E >> 5.8.0-rc5-100.g55927f9-default #1 openSUSE Tumbleweed (unreleased) >> [ 94.514084] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS >> rel-1.12.0-0-ga698c89-rebuilt.suse.com 04/01/2014 >> [ 94.514087] RIP: 0010:__might_sleep+0x6c/0x70 >> [ 94.514090] Code: 41 5c 41 5d e9 25 ff ff ff 48 8b 90 68 1a 00 00 48 8b >> 70 10 48 c7 c7 10 45 70 8f c6 05 4f a9 68 01 01 48 89 d1 e8 7a bb fc ff <0f> >> 0b eb c8 0f 1f 44 00 00 55 48 89 e5 41 57 41 56 41 55 49 89 fd >> [ 94.514092] RSP: 0018:ffff9ffa4ba1be00 EFLAGS: 00010286 >> [ 94.514093] RAX: 0000000000000000 RBX: ffff8dc82b503e00 RCX: >> 0000000000000489 >> [ 94.514094] RDX: 0000000000000001 RSI: 0000000000000096 RDI: >> 0000000000000247 >> [ 94.514095] RBP: ffffffff8f6ffa6b R08: 0000000000000004 R09: >> 0000000000000489 >> [ 94.514095] R10: 0000000000000000 R11: 0000000000000001 R12: >> 0000000000000039 >> [ 94.514096] R13: 0000000000000000 R14: 0000000000000001 R15: >> ffff8dc82b5045e4 >> [ 94.514098] FS: 00007fa00f1f9240(0000) GS:ffff8dcb0c000000(0000) >> knlGS:0000000000000000 >> [ 94.514099] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [ 94.514100] CR2: 0000557b53d25877 CR3: 00000004ca490005 CR4: >> 0000000000360ee0 >> [ 94.514103] DR0: 0000000000000000 DR1: 0000000000000000 DR2: >> 0000000000000000 >> [ 94.514104] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: >> 0000000000000400 >> [ 94.514105] Call Trace: >> [ 94.514821] ptrace_stop+0x1a9/0x300 > > This is already wrong. But > > Where does this __might_sleep() come from ??? I ses no blocking calls > in ptrace_stop(). Not to mention it is called with ->siglock held and > right after this lock is dropped we take tasklist_lock.
Decoded stacktrace: > ptrace_stop (include/linux/freezer.h:57 include/linux/freezer.h:67 > include/linux/freezer.h:128 include/linux/freezer.h:173 kernel/signal.c:2217) > > ptrace_do_notify (kernel/signal.c:2272) > ptrace_notify (arch/x86/include/asm/paravirt.h:656 > arch/x86/include/asm/qspinlock.h:55 include/linux/spinlock.h:211 > include/linux/spinlock_api_smp.h:167 include/linux/spinlock.h:403 > kernel/signal.c:2282) > syscall_trace_enter (include/linux/tracehook.h:73 > include/linux/tracehook.h:104 arch/x86/entry/common.c:159) > do_syscall_64 (arch/x86/entry/common.c:380) > entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:124) It is try_to_freeze_unsafe in try_to_freeze in freezable_schedule in ptrace_stop. > > How this connects to the debugging patch I sent? Did you see this > warning > without that patch? I suppose this made it appear: +CONFIG_PREEMPT_COUNT=y -# CONFIG_DEBUG_ATOMIC_SLEEP is not set +CONFIG_DEBUG_ATOMIC_SLEEP=y >> [ 94.514888] WARNING: CPU: 16 PID: 34171 at kernel/signal.c:2219 >> ptrace_stop+0x1d8/0x300 > ... >> [ 94.514899] RIP: 0010:ptrace_stop+0x1d8/0x300 > > This is WARN_ON(current->state) added to ptrace_stop(), this can explain > BUG_ON() in do_notify_parent() you reported. > > So, the tracee returns from schedule() with ->state != TASK_RUNNING ??? > This must not be possible. > > OK, perhaps task->state was changed by ptrace_unfreeze_traced()? this can > only happen if it races with ttwu(__TASK_TRACED) without ->siglock held, > nobody should do this. > > Strange. Please see my other e-mail, all this is with dbfb089d360b applied. Maybe it makes more sense now? thanks, -- js
