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[88.187.86.199]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b61ca2bcc3sm10312527f8f.27.2025.07.21.04.47.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 21 Jul 2025 04:47:44 -0700 (PDT) Message-ID: <96201a23-784b-4268-b011-a6912175d237@linaro.org> Date: Mon, 21 Jul 2025 13:47:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: apparent race condition in mttcg memory handling To: Michael Tokarev , QEMU Development References: Content-Language: en-US Cc: Jonathan Cameron , Pierrick Bouvier , =?UTF-8?Q?Alex_Benn=C3=A9e?= , Richard Henderson , Paolo Bonzini , Stefan Hajnoczi , Mark Cave-Ayland From: =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::435; envelope-from=philmd@linaro.org; helo=mail-wr1-x435.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, WEIRD_PORT=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org (Cc'ing few more developers) On 30/5/25 21:20, Michael Tokarev wrote: > Hi! > > For quite some time (almost whole day yesterday) I'm trying to find out > what's going on with mmtcg in qemu.  There's apparently a race condition > somewhere, like a use-after-free or something. > > It started as an incarnation of > https://gitlab.com/qemu-project/qemu/-/issues/1921 -- the same assertion > failure, but on an x86_64 host this time (it's also mentioned in that > issue). > > However, that particular assertion failure is not the only possible > outcome.  We're hitting multiple assertion failures or SIGSEGVs in > physmem.c and related files, - 4 or 5 different places so far. > > The problem here is that the bug is rather difficult to reproduce. > What I've been using so far was to make most host cores busy, and > specify amount of virtual CPUs close to actual host cores (threads). > > For example, on my 4-core, 8-threads notebook, I used `stress -c 8` > and ran qemu with -smp 10, to trigger this issue. However, on this > very notebook it is really difficult to trigger it, - it happens > every 30..50 runs or so. > > The reproducer I was using - it was just booting kernel, no user- > space is needed. Qemu crashes during kernel init, or it runs fine. > > I used regular kernel from debian sid: >  http://deb.debian.org/debian/pool/main/l/linux-signed-amd64/linux- > image-amd64_6.12.29-1_amd64.deb > Extract vmlinuz-6.12.29-amd64 from there. > > In order to simplify the reproducing, I created a tiny initrd with > just one executable in there, which does a poweroff: > > cat >poweroff.c <<'EOF' > #include > #include > > int main(void) { >   reboot(RB_POWER_OFF); >   sleep(5); >   return 0; > } > EOF > diet gcc -static -o init poweroff.c > echo init | cpio -o -H newc > initrd > > (it uses dietlibc, optional, just to make the initrd smaller). > > Now, the qemu invocation I used: > >  qemu-system-x86_64 -kernel vmlinuz -initrd initrd \ >    -append "console=ttyS0" \ >    -vga none -display none \ >    -serial file:/dev/tty \ >    -monitor stdio \ >    -m 256 \ >    -smp 16 > > This way, it either succeeds, terminating normally due to > the initrd hating the system, or it will segfault or assert > as per the issue. > > For a 64-core machine, I used -smp 64, and had 16..40 cores > being busy with other stuff.  Also, adding `nice' in front > of that command apparently helps. > > Now, to the various issues/places I've hit.  Here's a typical > output: > > ... > [    3.129806] smpboot: x86: Booting SMP configuration: > [    3.135789] .... node  #0, CPUs:        #1  #2  #3  #4  #5  #6  #7 > #8  #9 > [    0.000000] calibrate_delay_direct() failed to get a good estimate > for loops_per_jiffy. > [    0.000000] Probably due to long platform interrupts. Consider using > "lpj=" boot option. > [    0.000000] calibrate_delay_direct() failed to get a good estimate > for loops_per_jiffy. > [    0.000000] Probably due to long platform interrupts. Consider using > "lpj=" boot option. > [    0.000000] calibrate_delay_direct() failed to get a good estimate > for loops_per_jiffy. > [    0.000000] Probably due to long platform interrupts. Consider using > "lpj=" boot option. > [    0.000000] calibrate_delay_direct() failed to get a good estimate > for loops_per_jiffy. > [    0.000000] Probably due to long platform interrupts. Consider using > "lpj=" boot option. > [    4.494389] calibrate_delay_direct() failed to get a good estimate > for loops_per_jiffy. > [    4.494389] Probably due to long platform interrupts. Consider using > "lpj=" boot option. > [    4.494396] calibrate_delay_direct() failed to get a good estimate > for loops_per_jiffy. > [    4.494396] Probably due to long platform interrupts. Consider using > "lpj=" boot option. > [    4.494401] calibrate_delay_direct() failed to get a good estimate > for loops_per_jiffy. > [    4.494401] Probably due to long platform interrupts. Consider using > "lpj=" boot option. > [    4.494408] calibrate_delay_direct() failed to get a good estimate > for loops_per_jiffy. > [    4.494408] Probably due to long platform interrupts. Consider using > "lpj=" boot option. > [    4.494415] calibrate_delay_direct() failed to get a good estimate > for loops_per_jiffy. > [    4.494415] Probably due to long platform interrupts. Consider using > "lpj=" boot option. > [    5.864038] smp: Brought up 1 node, 10 CPUs > [    5.865772] smpboot: Total of 10 processors activated (25983.25 > BogoMIPS) > [    6.119683] Memory: 200320K/261624K available (16384K kernel code, > 2486K rwdata, 11780K rodata, 4148K init, 4956K bss, 53176K reserved, 0K > cma-reserved) > [    6.591933] devtmpfs: initialized > [    6.635844] x86/mm: Memory block size: 128MB > [    6.756849] clocksource: jiffies: mask: 0xffffffff max_cycles: > 0xffffffff, max_idle_ns: 7645041785100000 ns > [    6.774545] futex hash table entries: 4096 (order: 6, 262144 bytes, > linear) > [    6.840775] pinctrl core: initialized pinctrl subsystem > [    7.117085] NET: Registered PF_NETLINK/PF_ROUTE protocol family > [    7.165883] DMA: preallocated 128 KiB GFP_KERNEL pool for atomic > allocations > [    7.184243] DMA: preallocated 128 KiB GFP_KERNEL|GFP_DMA pool for > atomic allocations > [    7.188322] DMA: preallocated 128 KiB GFP_KERNEL|GFP_DMA32 pool for > atomic allocations > [    7.195902] audit: initializing netlink subsys (disabled) > [    7.223865] audit: type=2000 audit(1748628013.324:1): > state=initialized audit_enabled=0 res=1 > [    7.290904] thermal_sys: Registered thermal governor 'fair_share' > [    7.291980] thermal_sys: Registered thermal governor 'bang_bang' > [    7.295875] thermal_sys: Registered thermal governor 'step_wise' > [    7.299817] thermal_sys: Registered thermal governor 'user_space' > [    7.303804] thermal_sys: Registered thermal governor 'power_allocator' > [    7.316281] cpuidle: using governor ladder > [    7.331907] cpuidle: using governor menu > [    7.348199] acpiphp: ACPI Hot Plug PCI Controller Driver version: 0.5 > [    7.407802] PCI: Using configuration type 1 for base access > [    7.417386] mtrr: your CPUs had inconsistent fixed MTRR settings > [    7.418244] mtrr: your CPUs had inconsistent variable MTRR settings > [    7.419048] mtrr: your CPUs had inconsistent MTRRdefType settings > [    7.419938] mtrr: probably your BIOS does not setup all CPUs. > [    7.420691] mtrr: corrected configuration. > [    7.461270] kprobes: kprobe jump-optimization is enabled. All kprobes > are optimized if possible. > [    7.591938] HugeTLB: registered 2.00 MiB page size, pre-allocated 0 > pages > [    7.595986] HugeTLB: 28 KiB vmemmap can be freed for a 2.00 MiB page > [    7.816900] ACPI: Added _OSI(Module Device) > [    7.819950] ACPI: Added _OSI(Processor Device) > [    7.823873] ACPI: Added _OSI(3.0 _SCP Extensions) > [    7.827683] ACPI: Added _OSI(Processor Aggregator Device) > [    8.000944] ACPI: 1 ACPI AML tables successfully acquired and loaded > [    8.355952] ACPI: Interpreter enabled > [    8.406604] ACPI: PM: (supports S0 S3 S4 S5) > [    8.416143] ACPI: Using IOAPIC for interrupt routing > [    8.448173] PCI: Using host bridge windows from ACPI; if necessary, > use "pci=nocrs" and report a bug > [    8.468051] PCI: Using E820 reservations for host bridge windows > [    8.562534] ACPI: Enabled 2 GPEs in block 00 to 0F > [    9.153432] ACPI: PCI Root Bridge [PCI0] (domain 0000 [bus 00-ff]) > [    9.166585] acpi PNP0A03:00: _OSC: OS supports [ASPM ClockPM Segments > MSI HPX-Type3] > [    9.168452] acpi PNP0A03:00: _OSC: not requesting OS control; OS > requires [ExtendedConfig ASPM ClockPM MSI] > [    9.181933] acpi PNP0A03:00: fail to add MMCONFIG information, can't > access extended configuration space under this bridge > [    9.297562] acpiphp: Slot [2] registered > ... > [    9.369007] PCI host bridge to bus 0000:00 > [    9.376590] pci_bus 0000:00: root bus resource [io  0x0000-0x0cf7 > window] > [    9.379987] pci_bus 0000:00: root bus resource [io  0x0d00-0xffff > window] > [    9.383826] pci_bus 0000:00: root bus resource [mem > 0x000a0000-0x000bffff window] > [    9.387818] pci_bus 0000:00: root bus resource [mem > 0x10000000-0xfebfffff window] > [    9.393681] pci_bus 0000:00: root bus resource [mem > 0x100000000-0x17fffffff window] > [    9.396987] pci_bus 0000:00: root bus resource [bus 00-ff] > [    9.414378] pci 0000:00:00.0: [8086:1237] type 00 class 0x060000 > conventional PCI endpoint > [    9.477179] pci 0000:00:01.0: [8086:7000] type 00 class 0x060100 > conventional PCI endpoint > [    9.494836] pci 0000:00:01.1: [8086:7010] type 00 class 0x010180 > conventional PCI endpoint > [    9.527173] pci 0000:00:01.1: BAR 4 [io  0xc040-0xc04f] > Segmentation fault > > > So it breaks somewhere in PCI init, after SMP/CPUs has been inited > by the guest kernel. > > Thread 21 "qemu-system-x86" received signal SIGSEGV, Segmentation fault. > 0x0000555555e2e9c0 in section_covers_addr (section=0x7fff58307, > addr=182591488) at ../system/physmem.c:309 > 309         return int128_gethi(section->size) || > (gdb) p *section > Cannot access memory at address 0x7fff58307 > > This one has been seen multiple times. > > Thread 53 "qemu-system-x86" received signal SIGSEGV, Segmentation fault. > [Switching to Thread 0x7ffe8a7fc6c0 (LWP 104067)] > 0x0000555555e30382 in memory_region_section_get_iotlb > (cpu=0x5555584e0a90, section=0x7fff58c3eac0) at >              ../system/physmem.c:1002 > 1002        return section - d->map.sections; > d is NULL here > > > Thread 22 "qemu-system-x86" received signal SIGSEGV, Segmentation fault. > [Switching to Thread 0x7fff0bfff6c0 (LWP 57595)] > 0x0000555555e42c9a in memory_region_get_iommu (mr=0xffffffc1ffffffc1) at > include/exec/memory.h:1756 > 1756        if (mr->alias) { > (gdb) p *mr > Cannot access memory at address 0xffffffc1ffffffc1 > (gdb) frame 1 > #1  0x0000555555e42cb9 in memory_region_get_iommu (mr=0x7fff54239a10) at > include/exec/memory.h:1757 > 1757            return memory_region_get_iommu(mr->alias); > (gdb) p mr > $1 = (MemoryRegion *) 0x7fff54239a10 > > > [    9.222531] pci 0000:00:02.0: BAR 0 [mem 0xfebc0000-0xfebdffff] > [ > Thread 54 "qemu-system-x86" received signal SIGSEGV, Segmentation fault. > [Switching to Thread 0x7ffebeffd6c0 (LWP 14977)] > > (gdb) l > 1004    /* Called from RCU critical section */ > 1005    hwaddr memory_region_section_get_iotlb(CPUState *cpu, > 1006                                           MemoryRegionSection > *section) > 1007    { > 1008        AddressSpaceDispatch *d = flatview_to_dispatch(section->fv); > 1009        return section - d->map.sections; > 1010    } > 1011 > 1012    static int subpage_register(subpage_t *mmio, uint32_t start, > uint32_t end, > 1013                                uint16_t section); > > (gdb) p *section > $1 = {size = 4940204083636081308795136, mr = 0x7fff98739760, fv = > 0x7fff998f6fd0, >   offset_within_region = 0, offset_within_address_space = 0, readonly = > false, >   nonvolatile = false, unmergeable = 12} > > (gdb) p *section->fv > $2 = {rcu = {next = 0x0, func = 0x20281}, ref = 2555275280, ranges = > 0x7fff99486a60, nr = 0, >   nr_allocated = 0, dispatch = 0x0, root = 0xffffffc1ffffffc1} > > (gdb) bt > #0  0x0000555555e5118c in memory_region_section_get_iotlb > (cpu=cpu@entry=0x55555894fdf0, >     section=section@entry=0x7fff984e6810) at system/physmem.c:1009 > #1  0x0000555555e6e07a in tlb_set_page_full (cpu=cpu@entry=0x55555894fdf0, >     mmu_idx=mmu_idx@entry=6, addr=addr@entry=151134208, > full=full@entry=0x7ffebeffbd60) >     at accel/tcg/cputlb.c:1088 > #2  0x0000555555e70a92 in tlb_set_page_with_attrs > (cpu=cpu@entry=0x55555894fdf0, >     addr=addr@entry=151134208, paddr=paddr@entry=151134208, attrs=..., > prot=, >     mmu_idx=mmu_idx@entry=6, size=4096) at accel/tcg/cputlb.c:1193 > #3  0x0000555555d4ae44 in x86_cpu_tlb_fill (cs=0x55555894fdf0, > addr=151138272, >     size=, access_type=MMU_DATA_STORE, mmu_idx=6, > probe=, >     retaddr=0) at target/i386/tcg/system/excp_helper.c:624 > #4  0x0000555555e6e8cf in tlb_fill_align (cpu=0x55555894fdf0, > addr=151138272, >     type=MMU_DATA_LOAD, type@entry=MMU_DATA_STORE, mmu_idx=6, > memop=memop@entry=MO_8, >     size=-1739692016, size@entry=151138272, probe=true, ra=0) at accel/ > tcg/cputlb.c:1251 > #5  0x0000555555e6eb0d in probe_access_internal > (cpu=cpu@entry=0x55555894fdf0, >     addr=addr@entry=151138272, fault_size=fault_size@entry=0, >     access_type=access_type@entry=MMU_DATA_STORE, mmu_idx=, >     nonfault=nonfault@entry=true, phost=0x7ffebeffc0a8, > pfull=0x7ffebeffbfa0, retaddr=0, >     check_mem_cbs=false) at accel/tcg/cputlb.c:1371 > #6  0x0000555555e70c84 in probe_access_full_mmu (env=0x5555589529b0, > addr=addr@entry=151138272, >     size=size@entry=0, access_type=access_type@entry=MMU_DATA_STORE, > mmu_idx=, >     phost=phost@entry=0x7ffebeffc0a8, pfull=0x7ffebeffbfa0) at accel/ > tcg/cputlb.c:1439 > #7  0x0000555555d497c9 in ptw_translate (inout=0x7ffebeffc090, > addr=151138272) >     at target/i386/tcg/system/excp_helper.c:68 > #8  0x0000555555d49988 in mmu_translate (env=env@entry=0x5555589529b0, >     in=in@entry=0x7ffebeffc140, out=out@entry=0x7ffebeffc110, > err=err@entry=0x7ffebeffc120, >     ra=ra@entry=0) at target/i386/tcg/system/excp_helper.c:198 > #9  0x0000555555d4aece in get_physical_address (env=0x5555589529b0, > addr=18446741874686299840, >     access_type=MMU_DATA_LOAD, mmu_idx=4, out=0x7ffebeffc110, > err=0x7ffebeffc120, ra=0) >     at target/i386/tcg/system/excp_helper.c:597 > #10 x86_cpu_tlb_fill (cs=0x55555894fdf0, addr=18446741874686299840, > size=, >     access_type=MMU_DATA_LOAD, mmu_idx=4, probe=, > retaddr=0) >     at target/i386/tcg/system/excp_helper.c:617 > #11 0x0000555555e6e8cf in tlb_fill_align (cpu=0x55555894fdf0, > addr=18446741874686299840, >     type=type@entry=MMU_DATA_LOAD, mmu_idx=4, memop=MO_8, > memop@entry=MO_32, size=-1739692016, >     size@entry=3776, probe=false, ra=0) at accel/tcg/cputlb.c:1251 > #12 0x0000555555e6ed4d in mmu_lookup1 (cpu=cpu@entry=0x55555894fdf0, >     data=data@entry=0x7ffebeffc310, memop=memop@entry=MO_32, > mmu_idx=mmu_idx@entry=4, >     access_type=access_type@entry=MMU_DATA_LOAD, ra=ra@entry=0) at > accel/tcg/cputlb.c:1652 > #13 0x0000555555e6eea5 in mmu_lookup (cpu=cpu@entry=0x55555894fdf0, >     addr=addr@entry=18446741874686299840, oi=oi@entry=36, ra=ra@entry=0, >     type=type@entry=MMU_DATA_LOAD, l=l@entry=0x7ffebeffc310) at accel/ > tcg/cputlb.c:1755 > #14 0x0000555555e6f2f3 in do_ld4_mmu (cpu=cpu@entry=0x55555894fdf0, >     addr=addr@entry=18446741874686299840, oi=oi@entry=36, ra=ra@entry=0, >     access_type=access_type@entry=MMU_DATA_LOAD) at accel/tcg/ > cputlb.c:2364 > #15 0x0000555555e71dba in cpu_ldl_mmu (env=0x5555589529b0, > addr=18446741874686299840, oi=36, >     ra=0) at accel/tcg/ldst_common.c.inc:165 > #16 cpu_ldl_le_mmuidx_ra (env=env@entry=0x5555589529b0, > addr=addr@entry=18446741874686299840, >     mmu_idx=, ra=ra@entry=0) at accel/tcg/ > ldst_common.c.inc:308 > #17 0x0000555555db72da in do_interrupt64 (env=0x5555589529b0, intno=236, > is_int=0, error_code=0, >     next_eip=, is_hw=0) at target/i386/tcg/seg_helper.c:954 > #18 do_interrupt_all (cpu=cpu@entry=0x55555894fdf0, intno=236, > is_int=is_int@entry=0, >     error_code=error_code@entry=0, next_eip=next_eip@entry=0, > is_hw=is_hw@entry=1) >     at target/i386/tcg/seg_helper.c:1213 > #19 0x0000555555db884a in do_interrupt_x86_hardirq > (env=env@entry=0x5555589529b0, >     intno=, is_hw=is_hw@entry=1) at target/i386/tcg/ > seg_helper.c:1245 > #20 0x0000555555d4f06f in x86_cpu_exec_interrupt (cs=0x55555894fdf0, >     interrupt_request=) at target/i386/tcg/system/ > seg_helper.c:209 > #21 0x0000555555e660ed in cpu_handle_interrupt (cpu=0x55555894fdf0, > last_tb=) >     at accel/tcg/cpu-exec.c:851 > #22 cpu_exec_loop (cpu=cpu@entry=0x55555894fdf0, > sc=sc@entry=0x7ffebeffc580) >     at accel/tcg/cpu-exec.c:955 > #23 0x0000555555e663f1 in cpu_exec_setjmp (cpu=cpu@entry=0x55555894fdf0, >     sc=sc@entry=0x7ffebeffc580) at accel/tcg/cpu-exec.c:1033 >     type=type@entry=MMU_DATA_LOAD, l=l@entry=0x7ffebeffc310) at accel/ > tcg/cputlb.c:1755 > #14 0x0000555555e6f2f3 in do_ld4_mmu (cpu=cpu@entry=0x55555894fdf0, >     addr=addr@entry=18446741874686299840, oi=oi@entry=36, ra=ra@entry=0, >     access_type=access_type@entry=MMU_DATA_LOAD) at accel/tcg/ > cputlb.c:2364 > #15 0x0000555555e71dba in cpu_ldl_mmu (env=0x5555589529b0, > addr=18446741874686299840, oi=36, >     ra=0) at accel/tcg/ldst_common.c.inc:165 > #16 cpu_ldl_le_mmuidx_ra (env=env@entry=0x5555589529b0, > addr=addr@entry=18446741874686299840, >     mmu_idx=, ra=ra@entry=0) at accel/tcg/ > ldst_common.c.inc:308 > #17 0x0000555555db72da in do_interrupt64 (env=0x5555589529b0, intno=236, > is_int=0, error_code=0, >     next_eip=, is_hw=0) at target/i386/tcg/seg_helper.c:954 > #18 do_interrupt_all (cpu=cpu@entry=0x55555894fdf0, intno=236, > is_int=is_int@entry=0, >     error_code=error_code@entry=0, next_eip=next_eip@entry=0, > is_hw=is_hw@entry=1) >     at target/i386/tcg/seg_helper.c:1213 > #19 0x0000555555db884a in do_interrupt_x86_hardirq > (env=env@entry=0x5555589529b0, >     intno=, is_hw=is_hw@entry=1) at target/i386/tcg/ > seg_helper.c:1245 > #20 0x0000555555d4f06f in x86_cpu_exec_interrupt (cs=0x55555894fdf0, >     interrupt_request=) at target/i386/tcg/system/ > seg_helper.c:209 > #21 0x0000555555e660ed in cpu_handle_interrupt (cpu=0x55555894fdf0, > last_tb=) >     at accel/tcg/cpu-exec.c:851 > #22 cpu_exec_loop (cpu=cpu@entry=0x55555894fdf0, > sc=sc@entry=0x7ffebeffc580) >     at accel/tcg/cpu-exec.c:955 > #23 0x0000555555e663f1 in cpu_exec_setjmp (cpu=cpu@entry=0x55555894fdf0, >     sc=sc@entry=0x7ffebeffc580) at accel/tcg/cpu-exec.c:1033 > --Type for more, q to quit, c to continue without paging-- > #24 0x0000555555e66a5d in cpu_exec (cpu=cpu@entry=0x55555894fdf0) at > accel/tcg/cpu-exec.c:1059 > #25 0x0000555555d2bdc7 in tcg_cpu_exec (cpu=cpu@entry=0x55555894fdf0) >     at accel/tcg/tcg-accel-ops.c:80 > #26 0x0000555555d2c1c3 in mttcg_cpu_thread_fn > (arg=arg@entry=0x55555894fdf0) >     at accel/tcg/tcg-accel-ops-mttcg.c:94 > #27 0x0000555556056d90 in qemu_thread_start (args=0x5555589cdba0) at > util/qemu-thread-posix.c:541 > #28 0x00007ffff60e0b7b in ?? () from /lib/x86_64-linux-gnu/libc.so.6 > #29 0x00007ffff615e7b8 in ?? () from /lib/x86_64-linux-gnu/libc.so.6 > > > qemu-system-x86_64: ./include/exec/ram_addr.h:91: ramblock_ptr: > Assertion `offset_in_ramblock(block, offset)' failed. > > (gdb) bt > #0  0x00007ffff6076507 in abort () from /lib/x86_64-linux-gnu/libc.so.6 > #1  0x00007ffff6076420 in ?? () from /lib/x86_64-linux-gnu/libc.so.6 > #2  0x0000555555a047fa in ramblock_ptr (offset=281471527758833, > block=) >     at ./include/exec/ram_addr.h:91 > #3  0x0000555555a04c83 in ramblock_ptr (block=, > offset=) >     at system/physmem.c:2238 > #4  qemu_ram_ptr_length (lock=false, is_write=true, block= out>, addr=, >     size=0x0) at system/physmem.c:2430 > #5  qemu_map_ram_ptr (ram_block=, addr=) > at system/physmem.c:2443 > #6  0x0000555555e4af6b in memory_region_get_ram_ptr (mr=) > at system/memory.c:2452 > #7  0x0000555555e6e024 in tlb_set_page_full (cpu=cpu@entry=0x5555589f9f50, >     mmu_idx=mmu_idx@entry=4, addr=addr@entry=18446741874686296064, >     full=full@entry=0x7ffebd7f90b0) at accel/tcg/cputlb.c:1065 > #8  0x0000555555e70a92 in tlb_set_page_with_attrs > (cpu=cpu@entry=0x5555589f9f50, >     addr=addr@entry=18446741874686296064, paddr=paddr@entry=206749696, > attrs=..., >     prot=, mmu_idx=mmu_idx@entry=4, size=4096) at accel/ > tcg/cputlb.c:1193 > #9  0x0000555555d4ae44 in x86_cpu_tlb_fill (cs=0x5555589f9f50, > addr=18446741874686299840, >     size=, access_type=MMU_DATA_LOAD, mmu_idx=4, > probe=, retaddr=0) >     at target/i386/tcg/system/excp_helper.c:624 > #10 0x0000555555e6e8cf in tlb_fill_align (cpu=0x5555589f9f50, > addr=18446741874686299840, >     type=type@entry=MMU_DATA_LOAD, mmu_idx=4, memop=MO_8, > memop@entry=MO_32, size=-1115714056, >     size@entry=3776, probe=false, ra=0) at accel/tcg/cputlb.c:1251 > #11 0x0000555555e6ed4d in mmu_lookup1 (cpu=cpu@entry=0x5555589f9f50, >     data=data@entry=0x7ffebd7f9310, memop=memop@entry=MO_32, > mmu_idx=mmu_idx@entry=4, >     access_type=access_type@entry=MMU_DATA_LOAD, ra=ra@entry=0) at > accel/tcg/cputlb.c:1652 > #12 0x0000555555e6eea5 in mmu_lookup (cpu=cpu@entry=0x5555589f9f50, >     addr=addr@entry=18446741874686299840, oi=oi@entry=36, ra=ra@entry=0, >     type=type@entry=MMU_DATA_LOAD, l=l@entry=0x7ffebd7f9310) at accel/ > tcg/cputlb.c:1755 > #13 0x0000555555e6f2f3 in do_ld4_mmu (cpu=cpu@entry=0x5555589f9f50, >     addr=addr@entry=18446741874686299840, oi=oi@entry=36, ra=ra@entry=0, >     access_type=access_type@entry=MMU_DATA_LOAD) at accel/tcg/ > cputlb.c:2364 > #14 0x0000555555e71dba in cpu_ldl_mmu (env=0x5555589fcb10, > addr=18446741874686299840, oi=36, >     ra=0) at accel/tcg/ldst_common.c.inc:165 > #15 cpu_ldl_le_mmuidx_ra (env=env@entry=0x5555589fcb10, > addr=addr@entry=18446741874686299840, >     mmu_idx=, ra=ra@entry=0) at accel/tcg/ > ldst_common.c.inc:308 > #16 0x0000555555db72da in do_interrupt64 (env=0x5555589fcb10, intno=236, > is_int=0, error_code=0, >     next_eip=, is_hw=0) at target/i386/tcg/seg_helper.c:954 > #17 do_interrupt_all (cpu=cpu@entry=0x5555589f9f50, intno=236, > is_int=is_int@entry=0, >     error_code=error_code@entry=0, next_eip=next_eip@entry=0, > is_hw=is_hw@entry=1) >     at target/i386/tcg/seg_helper.c:1213 > #18 0x0000555555db884a in do_interrupt_x86_hardirq > (env=env@entry=0x5555589fcb10, >     intno=, is_hw=is_hw@entry=1) at target/i386/tcg/ > seg_helper.c:1245 > #19 0x0000555555d4f06f in x86_cpu_exec_interrupt (cs=0x5555589f9f50, >     interrupt_request=) at target/i386/tcg/system/ > seg_helper.c:209 > #20 0x0000555555e660ed in cpu_handle_interrupt (cpu=0x5555589f9f50, > last_tb=) >     at accel/tcg/cpu-exec.c:851 > #21 cpu_exec_loop (cpu=cpu@entry=0x5555589f9f50, > sc=sc@entry=0x7ffebd7f9580) >     at accel/tcg/cpu-exec.c:955 > #22 0x0000555555e663f1 in cpu_exec_setjmp (cpu=cpu@entry=0x5555589f9f50, >     sc=sc@entry=0x7ffebd7f9580) at accel/tcg/cpu-exec.c:1033 > #23 0x0000555555e66a5d in cpu_exec (cpu=cpu@entry=0x5555589f9f50) at > accel/tcg/cpu-exec.c:1059 > #24 0x0000555555d2bdc7 in tcg_cpu_exec (cpu=cpu@entry=0x5555589f9f50) >     at accel/tcg/tcg-accel-ops.c:80 > #25 0x0000555555d2c1c3 in mttcg_cpu_thread_fn > (arg=arg@entry=0x5555589f9f50) >     at accel/tcg/tcg-accel-ops-mttcg.c:94 > #26 0x0000555556056d90 in qemu_thread_start (args=0x55555856bf60) at > util/qemu-thread-posix.c:541 > #27 0x00007ffff60e0b7b in ?? () from /lib/x86_64-linux-gnu/libc.so.6 > #28 0x00007ffff615e7b8 in ?? () from /lib/x86_64-linux-gnu/libc.so.6 > > (gdb) frame 2 > #2  0x0000555555a047fa in ramblock_ptr (offset=281471527758833, > block=) >     at ./include/exec/ram_addr.h:91 > 91          assert(offset_in_ramblock(block, offset)); > > (gdb) l > 86          return (b && b->host && offset < b->used_length) ? true : > false; > 87      } > 88 > 89      static inline void *ramblock_ptr(RAMBlock *block, ram_addr_t > offset) > 90      { > 91          assert(offset_in_ramblock(block, offset)); > 92          return (char *)block->host + offset; > 93      } > 94 > 95      static inline unsigned long int ramblock_recv_bitmap_offset(void > *host_addr, > > > [    9.439487] pci 0000:00:02.0: BAR 1 [io  0xc000-0xc03f] > > Thread 65 "qemu-system-x86" received signal SIGSEGV, Segmentation fault. > [Switching to Thread 0x7ffe9cff96c0 (LWP 15472)] > phys_page_find (d=d@entry=0x7fff905ec880, addr=addr@entry=111288320) at > system/physmem.c:337 > 337         if (section_covers_addr(§ions[lp.ptr], addr)) { > (gdb) l > 332             } > 333             p = nodes[lp.ptr]; > 334             lp = p[(index >> (i * P_L2_BITS)) & (P_L2_SIZE - 1)]; > 335         } > 336 > 337         if (section_covers_addr(§ions[lp.ptr], addr)) { > 338             return §ions[lp.ptr]; > 339         } else { > 340             return §ions[PHYS_SECTION_UNASSIGNED]; > 341         } > (gdb) > > > I was doing a bisection between 9.2.0 and 10.0.0, since we observed > this issue happening wiht 10.0 but not - with 9.2.  So some of the > above failures might be somewhere from the middle between 9.2 and > 10.0.  However, I was able to trigger some of the failures with > 9.2.0, though with much less probability.  And some can be triggered > in current master too, with much better probability. > > On my 4-core notebook, the above command line fails every 20..50 run. > > I was never able to reproduce the assertion failure as shown in !1921. > > As of now, this issue is hitting debian trixie, - in debci, when a > package which creates a guest image tries to run qemu but in the > debci environment there's no kvm available, so it resorts to tcg. > > On IRC, Manos Pitsidianakis noted that he was debugging use-after-free > with MemoryRegion recently, and posted a patch which can help a bit: > https://people.linaro.org/~manos.pitsidianakis/backtrace.diff > > I'm not sure where to go from here. > > Just collecting everything we have now. > > Thanks, > > /mjt >