• Yonghong Song's avatar
    bpf, mm: Fix lockdep warning triggered by stack_map_get_build_id_offset() · 2f1aaf3e
    Yonghong Song authored
    Currently the bpf selftest "get_stack_raw_tp" triggered the warning:
    
      [ 1411.304463] WARNING: CPU: 3 PID: 140 at include/linux/mmap_lock.h:164 find_vma+0x47/0xa0
      [ 1411.304469] Modules linked in: bpf_testmod(O) [last unloaded: bpf_testmod]
      [ 1411.304476] CPU: 3 PID: 140 Comm: systemd-journal Tainted: G        W  O      5.14.0+ #53
      [ 1411.304479] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
      [ 1411.304481] RIP: 0010:find_vma+0x47/0xa0
      [ 1411.304484] Code: de 48 89 ef e8 ba f5 fe ff 48 85 c0 74 2e 48 83 c4 08 5b 5d c3 48 8d bf 28 01 00 00 be ff ff ff ff e8 2d 9f d8 00 85 c0 75 d4 <0f> 0b 48 89 de 48 8
      [ 1411.304487] RSP: 0018:ffffabd440403db8 EFLAGS: 00010246
      [ 1411.304490] RAX: 0000000000000000 RBX: 00007f00ad80a0e0 RCX: 0000000000000000
      [ 1411.304492] RDX: 0000000000000001 RSI: ffffffff9776b144 RDI: ffffffff977e1b0e
      [ 1411.304494] RBP: ffff9cf5c2f50000 R08: ffff9cf5c3eb25d8 R09: 00000000fffffffe
      [ 1411.304496] R10: 0000000000000001 R11: 00000000ef974e19 R12: ffff9cf5c39ae0e0
      [ 1411.304498] R13: 0000000000000000 R14: 0000000000000000 R15: ffff9cf5c39ae0e0
      [ 1411.304501] FS:  00007f00ae754780(0000) GS:ffff9cf5fba00000(0000) knlGS:0000000000000000
      [ 1411.304504] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      [ 1411.304506] CR2: 000000003e34343c CR3: 0000000103a98005 CR4: 0000000000370ee0
      [ 1411.304508] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      [ 1411.304510] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
      [ 1411.304512] Call Trace:
      [ 1411.304517]  stack_map_get_build_id_offset+0x17c/0x260
      [ 1411.304528]  __bpf_get_stack+0x18f/0x230
      [ 1411.304541]  bpf_get_stack_raw_tp+0x5a/0x70
      [ 1411.305752] RAX: 0000000000000000 RBX: 5541f689495641d7 RCX: 0000000000000000
      [ 1411.305756] RDX: 0000000000000001 RSI: ffffffff9776b144 RDI: ffffffff977e1b0e
      [ 1411.305758] RBP: ffff9cf5c02b2f40 R08: ffff9cf5ca7606c0 R09: ffffcbd43ee02c04
      [ 1411.306978]  bpf_prog_32007c34f7726d29_bpf_prog1+0xaf/0xd9c
      [ 1411.307861] R10: 0000000000000001 R11: 0000000000000044 R12: ffff9cf5c2ef60e0
      [ 1411.307865] R13: 0000000000000005 R14: 0000000000000000 R15: ffff9cf5c2ef6108
      [ 1411.309074]  bpf_trace_run2+0x8f/0x1a0
      [ 1411.309891] FS:  00007ff485141700(0000) GS:ffff9cf5fae00000(0000) knlGS:0000000000000000
      [ 1411.309896] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      [ 1411.311221]  syscall_trace_enter.isra.20+0x161/0x1f0
      [ 1411.311600] CR2: 00007ff48514d90e CR3: 0000000107114001 CR4: 0000000000370ef0
      [ 1411.312291]  do_syscall_64+0x15/0x80
      [ 1411.312941] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      [ 1411.313803]  entry_SYSCALL_64_after_hwframe+0x44/0xae
      [ 1411.314223] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
      [ 1411.315082] RIP: 0033:0x7f00ad80a0e0
      [ 1411.315626] Call Trace:
      [ 1411.315632]  stack_map_get_build_id_offset+0x17c/0x260
    
    To reproduce, first build `test_progs` binary:
    
      make -C tools/testing/selftests/bpf -j60
    
    and then run the binary at tools/testing/selftests/bpf directory:
    
      ./test_progs -t get_stack_raw_tp
    
    The warning is due to commit 5b78ed24 ("mm/pagemap: add mmap_assert_locked()
    annotations to find_vma*()") which added mmap_assert_locked() in find_vma()
    function. The mmap_assert_locked() function asserts that mm->mmap_lock needs
    to be held. But this is not the case for bpf_get_stack() or bpf_get_stackid()
    helper (kernel/bpf/stackmap.c), which uses mmap_read_trylock_non_owner()
    instead. Since mm->mmap_lock is not held in bpf_get_stack[id]() use case,
    the above warning is emitted during test run.
    
    This patch fixed the issue by (1). using mmap_read_trylock() instead of
    mmap_read_trylock_non_owner() to satisfy lockdep checking in find_vma(), and
    (2). droping lockdep for mmap_lock right before the irq_work_queue(). The
    function mmap_read_trylock_non_owner() is also removed since after this
    patch nobody calls it any more.
    
    Fixes: 5b78ed24 ("mm/pagemap: add mmap_assert_locked() annotations to find_vma*()")
    Suggested-by: default avatarJason Gunthorpe <jgg@ziepe.ca>
    Signed-off-by: default avatarYonghong Song <yhs@fb.com>
    Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    Reviewed-by: default avatarLiam R. Howlett <Liam.Howlett@oracle.com>
    Cc: Luigi Rizzo <lrizzo@google.com>
    Cc: Jason Gunthorpe <jgg@ziepe.ca>
    Cc: linux-mm@kvack.org
    Link: https://lore.kernel.org/bpf/20210909155000.1610299-1-yhs@fb.com
    2f1aaf3e
stackmap.c 18.7 KB