lkml.org 
[lkml]   [2020]   [Jun]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: mm lock issue while booting Linux on 5.8-rc1 for RISC-V
    From
    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.

    >
    > 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.

    \
     
     \ /
      Last update: 2020-06-16 20:07    [W:3.093 / U:0.004 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site