Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
* Yonghong Song <yhs@xxxxxx> [210909 11:50]:
> Current bpf-next 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 5b78ed24e8ec("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.
>
> Cc: Luigi Rizzo <lrizzo@xxxxxxxxxx>
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxx>
> Fixes: 5b78ed24e8ec("mm/pagemap: add mmap_assert_locked() annotations to find_vma*()")
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> ---
> include/linux/mmap_lock.h | 9 ---------
> kernel/bpf/stackmap.c | 10 ++++++++--
> 2 files changed, 8 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
> index 0540f0156f58..3af8f7fb067d 100644
> --- a/include/linux/mmap_lock.h
> +++ b/include/linux/mmap_lock.h
> @@ -144,15 +144,6 @@ static inline void mmap_read_unlock(struct mm_struct *mm)
> __mmap_lock_trace_released(mm, false);
> }
>
> -static inline bool mmap_read_trylock_non_owner(struct mm_struct *mm)
> -{
> - if (mmap_read_trylock(mm)) {
> - rwsem_release(&mm->mmap_lock.dep_map, _RET_IP_);
> - return true;
> - }
> - return false;
> -}
> -
> static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)
> {
> up_read_non_owner(&mm->mmap_lock);
> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
> index e8eefdf8cf3e..09a3fd97d329 100644
> --- a/kernel/bpf/stackmap.c
> +++ b/kernel/bpf/stackmap.c
> @@ -179,7 +179,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
> * with build_id.
> */
> if (!user || !current || !current->mm || irq_work_busy ||
> - !mmap_read_trylock_non_owner(current->mm)) {
> + !mmap_read_trylock(current->mm)) {
> /* cannot access current->mm, fall back to ips */
> for (i = 0; i < trace_nr; i++) {
> id_offs[i].status = BPF_STACK_BUILD_ID_IP;
> @@ -204,9 +204,15 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
> }
>
> if (!work) {
> - mmap_read_unlock_non_owner(current->mm);
> + mmap_read_unlock(current->mm);
> } else {
> work->mm = current->mm;
> +
> + /* The lock will be released once we're out of interrupt
> + * context. Tell lockdep that we've released it now so
> + * it doesn't complain that we forgot to release it.
> + */
> + rwsem_release(¤t->mm->mmap_lock.dep_map, _RET_IP_);
> irq_work_queue(&work->irq_work);
> }
> }
> --
> 2.30.2
>
>
