Messages in this thread | | | Subject | Re: mm lock issue while booting Linux on 5.8-rc1 for RISC-V | From | Alex Ghiti <> | Date | Tue, 16 Jun 2020 15:18:21 -0400 |
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Le 6/16/20 à 2:07 PM, Palmer Dabbelt a écrit : > On Tue, 16 Jun 2020 10:54:51 PDT (-0700), atishp@atishpatra.org wrote: >> On Tue, Jun 16, 2020 at 3:45 AM Michel Lespinasse <walken@google.com> >> wrote: >>> >>> I am also unable to reproduce the issue so far. >>> >>> I wanted to point to a few things in case this helps: >>> - Commit 42fc541404f2 was bisected as the cause. This commit changes >>> walk_page_range_novma() to use mmap_assert_locked() instead of >>> lockdep_assert_held() >>> - mmap_assert_locked() checks lockdep_assert_held(), but also checks >>> that the rwsem itself is locked. >>> >>> Now how could lockdep think the lock is held, but the lock itself is >>> not marked as locked ??? >>> >>> I'm not sure if it helps at all, but a few commits earlier, >>> 0cc55a0213a0 introduces mmap_read_trylock_non_owner(), which is used >>> exclusively by stackmap, and does the opposite: it acquires the mmap >>> lock without telling lockdep about it. I can't see any smoking gun >>> linking this to our bug, but I thought it may be worth mentioning as >>> it involves the same suspects (stackmap and the difference between >>> owning the lock vs lockdep thinking we own the lock). >>> >>> I'm sorry, that's only how far I was able to go on this bug - I'm not >>> sure how to investigate it further as I can not reproduce the issue... >>> >>> On Tue, Jun 16, 2020 at 1:40 AM Palmer Dabbelt <palmer@dabbelt.com> >>> wrote: >>> > >>> > On Mon, 15 Jun 2020 21:51:08 PDT (-0700), shorne@gmail.com wrote: >>> > > On Tue, Jun 16, 2020 at 06:57:47AM +0900, Stafford Horne wrote: >>> > >> On Mon, Jun 15, 2020 at 12:28:11AM -0700, Atish Patra wrote: >>> > >> > Hi, >>> > >> > I encountered the following issue while booting 5.8-rc1 on >>> Qemu for RV64. >>> > >> > I added additional dump_stack and observed that it's >>> happening in bpf free path. >>> > >> > It happens always if CONFIG_DEBUG_VM is enabled. VM_BUG_ON_MM is >>> > >> > compiled away without that. >>> > >> > >>> ------------------------------------------------------------------------ >>> >>> > >> > forked to background, child pid 113 >>> > >> > [ 10.328850] CPU: 3 PID: 51 Comm: kworker/3:1 Not tainted >>> > >> > 5.8.0-rc1-dirty #732 >>> > >> > [ 10.331739] Workqueue: events bpf_prog_free_deferred >>> > >> > [ 10.334133] Call Trace: >>> > >> > [ 10.338039] [<ffffffe000202698>] walk_stackframe+0x0/0xa4 >>> > >> > [ 10.339988] [<ffffffe000202880>] show_stack+0x2e/0x3a >>> > >> > [ 10.340902] [<ffffffe00047074c>] dump_stack+0x72/0x8c >>> > >> > [ 10.341451] [<ffffffe0002db4ce>] >>> mmap_assert_locked.part.13+0x14/0x1c >>> > >> > [ 10.342131] [<ffffffe0002db330>] >>> walk_page_range_novma+0x0/0x4e >>> > >> > [ 10.342973] [<ffffffe000204f94>] >>> set_direct_map_invalid_noflush+0x66/0x6e >>> > >> > [ 10.343917] [<ffffffe0002e0706>] __vunmap+0xe8/0x212 >>> > >> > [ 10.344680] [<ffffffe0002e0882>] __vfree+0x22/0x6e >>> > >> > [ 10.345270] [<ffffffe0002e0902>] vfree+0x34/0x56 >>> > >> > [ 10.345834] [<ffffffe00027d752>] __bpf_prog_free+0x2c/0x36 >>> > >> > [ 10.346529] [<ffffffe0002801a2>] >>> bpf_prog_free_deferred+0x74/0x8a >>> > >> > [ 10.347394] [<ffffffe000219c70>] process_one_work+0x13a/0x272 >>> > >> > [ 10.348239] [<ffffffe00021a4b4>] worker_thread+0x50/0x2e4 >>> > >> > [ 10.348900] [<ffffffe00021ed98>] kthread+0xfc/0x10a >>> > >> > [ 10.349470] [<ffffffe0002013da>] ret_from_exception+0x0/0xc >>> > >> > [ 10.354405] mm ffffffe001018600 mmap 0000000000000000 >>> seqnum 0 task_size 0 >>> > >> > [ 10.354405] get_unmapped_area 0000000000000000 >>> > >> > [ 10.354405] mmap_base 0 mmap_legacy_base 0 highest_vm_end 0 >>> > >> > [ 10.354405] pgd ffffffe001074000 mm_users 2 mm_count 1 >>> > >> > pgtables_bytes 8192 map_count 0 >>> > >> > [ 10.354405] hiwater_rss 0 hiwater_vm 0 total_vm 0 locked_vm 0 >>> > >> > [ 10.354405] pinned_vm 0 data_vm 0 exec_vm 0 stack_vm 0 >>> > >> > [ 10.354405] start_code ffffffe000200000 end_code >>> ffffffe00084acc2 >>> > >> > start_data 0 end_data ffffffe00106dfe4 >>> > >> > [ 10.354405] start_brk 0 brk ffffffe0010bd6d0 start_stack 0 >>> > >> > [ 10.354405] arg_start 0 arg_end 0 env_start 0 env_end 0 >>> > >> > [ 10.354405] binfmt 0000000000000000 flags 0 core_state >>> 0000000000000000 >>> > >> > [ 10.354405] ioctx_table 0000000000000000 >>> > >> > [ 10.354405] exe_file 0000000000000000 >>> > >> > [ 10.354405] tlb_flush_pending 0 >>> > >> > [ 10.354405] def_flags: 0x0() >>> > >> > [ 10.369325] ------------[ cut here ]------------ >>> > >> > [ 10.370763] kernel BUG at include/linux/mmap_lock.h:81! >>> > >> > [ 10.375235] Kernel BUG [#1] >>> > >> > [ 10.377198] Modules linked in: >>> > >> > [ 10.378931] CPU: 3 PID: 51 Comm: kworker/3:1 Not tainted >>> 5.8.0-rc1-dirty #732 >>> > >> > [ 10.380179] Workqueue: events bpf_prog_free_deferred >>> > >> > [ 10.381270] epc: ffffffe0002db4d4 ra : ffffffe0002db4d4 sp >>> : ffffffe3eaea7c70 >>> > >> > [ 10.382561] gp : ffffffe00106d950 tp : ffffffe3ef752f80 t0 : >>> > >> > ffffffe0010836e8 >>> > >> > [ 10.383996] t1 : 0000000000000064 t2 : 0000000000000000 s0 : >>> > >> > ffffffe3eaea7c90 >>> > >> > [ 10.385119] s1 : ffffffe001018600 a0 : 0000000000000289 a1 : >>> > >> > 0000000000000020 >>> > >> > [ 10.386099] a2 : 0000000000000005 a3 : 0000000000000000 a4 : >>> > >> > ffffffe001012758 >>> > >> > [ 10.387294] a5 : 0000000000000000 a6 : 0000000000000102 a7 : >>> > >> > 0000000000000006 >>> > >> > [ 10.388265] s2 : ffffffe3f00674c0 s3 : ffffffe00106e108 s4 : >>> > >> > ffffffe00106e100 >>> > >> > [ 10.389250] s5 : ffffffe00106e908 s6 : 0000000000000000 s7 : >>> > >> > 6db6db6db6db6db7 >>> > >> > [ 10.390272] s8 : 0000000000000001 s9 : ffffffe00021a4f8 s10: >>> > >> > ffffffffffffffff >>> > >> > [ 10.391293] s11: ffffffe3f0066600 t3 : 000000000001a7a8 t4 : >>> > >> > 000000000001a7a8 >>> > >> > [ 10.392314] t5 : 0000000000000000 t6 : ffffffe00107b76b >>> > >> > [ 10.393096] status: 0000000000000120 badaddr: >>> 0000000000000000 >>> > >> > cause: 0000000000000003 >>> > >> > [ 10.397755] ---[ end trace 861659596ac28841 ]--- >>> > >> > >>> --------------------------------------------------------------------------------------------------- >>> > >> > >>> > >> > I haven't had the chance to bisect to figure out which commit >>> caused >>> > >> > the issue. Just wanted >>> > >> > to check if it is a known issue already. >>> > >> >>> > >> Hi Atish, >>> > >> >>> > >> Note, I am getting the same (just now) when booting v5.8-rc1 on >>> OpenRISC. If >>> > >> you have any updates please post back. I will try to look into >>> this today or >>> > >> tomorrow. >>> > > >>> > > I have bisected this to, 42fc541404f249778e752ab39c8bc25fcb2dbe1e: >>> > > >>> > > mmap locking API: add mmap_assert_locked() and >>> mmap_assert_write_locked() >>> > > >>> > > This should have just changed the existing lockdep api's but >>> something has >>> > > changed. I haven't had time to look at it yet. >>> > > >>> > > Ccing: Michel Lespinasse <walken@google.com> >>> > >>> > This isn't manifesting on boot for me, on either rc1 or that >>> commit. I'm >>> > running a simple buildroot-based userspace, so I doubt anything is >>> triggering >>> > BPF. I don't run the BPF selftests, as they're a bit of a pain >>> (IIRC they >>> > don't cross compile and need LLVM) -- does anyone have a userspace >>> I can use to >>> > trigger the bug? >>> >> I am also using buildroot based userspace but it's a bit bulky because >> of my config. >> You can access it from here: >> https://wdc.box.com/s/r8j0d5ynp5gr27n2wo124xi9t8fp0tls > > I'm up to ~900M trying to get enough of a userspace to run the BPF > selftests, > so this would be way better. Unfortunately I'm not actually getting the > crash with your rootfs. >
I have what looks like the same bug by simply using the TEST_BPF config, with a very small rootfs generated by buildroot if that can help.
>> >> A defconfig build & boot in Qemu with above userspace is sufficient to >> trigger the bug. >> >> FYI: I noticed the kernel bug message every time during ssh-key >> generation. Not sure if that is related. >> >>> >>> >>> -- >>> Michel "Walken" Lespinasse >>> A program is never fully debugged until the last user dies. >
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