On 11/20/18 9:42 PM, Kirill A. Shutemov wrote:
On Tue, Nov 20, 2018 at 08:10:51PM +0800, Yang Shi wrote:
On 11/20/18 4:57 PM, Kirill A. Shutemov wrote:
On Fri, Nov 16, 2018 at 08:56:04AM -0800, Yang Shi wrote:
a8dda165ec vfree: add debug might_sleep()
dd2283f260 mm: mmap: zap pages with read mmap_sem in munmap
5929a1f0ff Merge tag 'riscv-for-linus-4.20-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/palmer/riscv-linux
0bc80e3cb0 Add linux-next specific files for 20181114
+-----------------------------------------------------+------------+------------+------------+---------------+
| | a8dda165ec | dd2283f260 | 5929a1f0ff | next-20181114 |
+-----------------------------------------------------+------------+------------+------------+---------------+
| boot_successes | 314 | 178 | 190 | 168 |
| boot_failures | 393 | 27 | 21 | 40 |
| WARNING:held_lock_freed | 383 | 23 | 17 | 39 |
| is_freeing_memory#-#,with_a_lock_still_held_there | 383 | 23 | 17 | 39 |
| BUG:unable_to_handle_kernel | 5 | 2 | 4 | 1 |
| Oops:#[##] | 9 | 3 | 4 | 1 |
| EIP:debug_check_no_locks_freed | 9 | 3 | 4 | 1 |
| Kernel_panic-not_syncing:Fatal_exception | 9 | 3 | 4 | 1 |
| Mem-Info | 4 | 1 | | |
| invoked_oom-killer:gfp_mask=0x | 1 | 1 | | |
| WARNING:at_kernel/locking/lockdep.c:#lock_downgrade | 0 | 6 | 4 | 7 |
| EIP:lock_downgrade | 0 | 6 | 4 | 7 |
+-----------------------------------------------------+------------+------------+------------+---------------+
[ 96.288009] random: get_random_u32 called from arch_rnd+0x3c/0x70 with crng_init=0
[ 96.359626] input_id (331) used greatest stack depth: 6360 bytes left
[ 96.749228] grep (358) used greatest stack depth: 6336 bytes left
[ 96.921470] network.sh (341) used greatest stack depth: 6212 bytes left
[ 97.262340]
[ 97.262587] =========================
[ 97.263072] WARNING: held lock freed!
[ 97.263536] 4.19.0-06969-gdd2283f #1 Not tainted
[ 97.264110] -------------------------
[ 97.264575] udevd/198 is freeing memory 9c16c930-9c16c99b, with a lock still held there!
[ 97.265542] (ptrval) (&anon_vma->rwsem){....}, at: unlink_anon_vmas+0x14e/0x420
[ 97.266450] 1 lock held by udevd/198:
[ 97.266924] #0: (ptrval) (&mm->mmap_sem){....}, at: __do_munmap+0x531/0x730
I have not figured out what this is caused by. But, the below warning looks
more confusing. This might be caused by the below one.
I *think* we need to understand more about what detached VMAs mean for
rmap. The anon_vma for these VMAs still reachable for the rmap and
therefore VMA too. I don't quite grasp what is implications of this, but
it doesn't look good.
I'm supposed before accessing anon_vma, VMA need to be found by find_vma()
first, right? But, finding VMA need hold mmap_sem, once detach VMAs is
called, others should not be able to find the VMAs anymore. So, the anon_vma
should not be reachable except the munmap caller.
No. anon_vma can be reached from page->mapping. The page can be reached
during physcal memory scan or if the page is shared (across fork()). None
of these accesses require mmap_sem.
If they don't require mmap_sem at all, this problem should be valid
regardless of the optimization. We just downgraded write mmap_sem to
read, but still hold it.
