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charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <60f2b14f-8cef-f515-9cf5-bdbc02d9c63c@shipmail.org> X-Operating-System: Linux phenom 5.7.0-1-amd64 Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Thu, Jul 30, 2020 at 06:45:14PM +0200, Thomas Hellström (Intel) wrote: > > On 7/30/20 3:17 PM, Daniel Vetter wrote: > > On Thu, Jul 30, 2020 at 2:17 PM Thomas Hellström (Intel) > > wrote: > > > > > > On 7/28/20 3:58 PM, Daniel Vetter wrote: > > > > GPU drivers need this in their shrinkers, to be able to throw out > > > > mmap'ed buffers. Note that we also need dma_resv_lock in shrinkers, > > > > but that loop is resolved by trylocking in shrinkers. > > > > > > > > So full hierarchy is now (ignore some of the other branches we already > > > > have primed): > > > > > > > > mmap_read_lock -> dma_resv -> shrinkers -> i_mmap_lock_write > > > > > > > > I hope that's not inconsistent with anything mm or fs does, adding > > > > relevant people. > > > > > > > Looks OK to me. The mapping_dirty_helpers run under the i_mmap_lock, but > > > don't allocate any memory AFAICT. > > > > > > Since huge page-table-entry splitting may happen under the i_mmap_lock > > > from unmap_mapping_range() it might be worth figuring out how new page > > > directory pages are allocated, though. > > ofc I'm not an mm expert at all, but I did try to scroll through all > > i_mmap_lock_write/read callers. Found the following: > > > > - kernel/events/uprobes.c in build_map_info: > > > > /* > > * Needs GFP_NOWAIT to avoid i_mmap_rwsem recursion through > > * reclaim. This is optimistic, no harm done if it fails. > > */ > > > > - I got lost in the hugetlb.c code and couldn't convince myself it's > > not allocating page directories at various levels with something else > > than GFP_KERNEL. > > > > So looks like the recursion is clearly there and known, but the > > hugepage code is too complex and flying over my head. > > -Daniel > > OK, so I inverted your annotation and ran a memory hog, and got the below > splat. So clearly your proposed reclaim->i_mmap_lock locking order is an > already established one. > > So > > Reviewed-by: Thomas Hellström No one complaining that this is a terrible idea and two reviews from people who know stuff, so I went ahead and pushed this to drm-misc-next. Thanks for taking a look at this. -Daniel > > 8<--------------------------------------------------------------------------------------------- > > [  308.324654] WARNING: possible circular locking dependency detected > [  308.324655] 5.8.0-rc2+ #16 Not tainted > [  308.324656] ------------------------------------------------------ > [  308.324657] kswapd0/98 is trying to acquire lock: > [  308.324658] ffff92a16f758428 (&mapping->i_mmap_rwsem){++++}-{3:3}, at: > rmap_walk_file+0x1c0/0x2f0 > [  308.324663] >                but task is already holding lock: > [  308.324664] ffffffffb0960240 (fs_reclaim){+.+.}-{0:0}, at: > __fs_reclaim_acquire+0x5/0x30 > [  308.324666] >                which lock already depends on the new lock. > > [  308.324667] >                the existing dependency chain (in reverse order) is: > [  308.324667] >                -> #1 (fs_reclaim){+.+.}-{0:0}: > [  308.324670]        fs_reclaim_acquire+0x34/0x40 > [  308.324672]        dma_resv_lockdep+0x186/0x224 > [  308.324675]        do_one_initcall+0x5d/0x2c0 > [  308.324676]        kernel_init_freeable+0x222/0x288 > [  308.324678]        kernel_init+0xa/0x107 > [  308.324679]        ret_from_fork+0x1f/0x30 > [  308.324680] >                -> #0 (&mapping->i_mmap_rwsem){++++}-{3:3}: > [  308.324682]        __lock_acquire+0x119f/0x1fc0 > [  308.324683]        lock_acquire+0xa4/0x3b0 > [  308.324685]        down_read+0x2d/0x110 > [  308.324686]        rmap_walk_file+0x1c0/0x2f0 > [  308.324687]        page_referenced+0x133/0x150 > [  308.324689]        shrink_active_list+0x142/0x610 > [  308.324690]        balance_pgdat+0x229/0x620 > [  308.324691]        kswapd+0x200/0x470 > [  308.324693]        kthread+0x11f/0x140 > [  308.324694]        ret_from_fork+0x1f/0x30 > [  308.324694] >                other info that might help us debug this: > > [  308.324695]  Possible unsafe locking scenario: > > [  308.324695]        CPU0                    CPU1 > [  308.324696]        ----                    ---- > [  308.324696]   lock(fs_reclaim); > [  308.324697] lock(&mapping->i_mmap_rwsem); > [  308.324698]                                lock(fs_reclaim); > [  308.324699]   lock(&mapping->i_mmap_rwsem); > [  308.324699] >                 *** DEADLOCK *** > > [  308.324700] 1 lock held by kswapd0/98: > [  308.324701]  #0: ffffffffb0960240 (fs_reclaim){+.+.}-{0:0}, at: > __fs_reclaim_acquire+0x5/0x30 > [  308.324702] >                stack backtrace: > [  308.324704] CPU: 1 PID: 98 Comm: kswapd0 Not tainted 5.8.0-rc2+ #16 > [  308.324705] Hardware name: VMware, Inc. VMware Virtual Platform/440BX > Desktop Reference Platform, BIOS 6.00 07/29/2019 > [  308.324706] Call Trace: > [  308.324710]  dump_stack+0x92/0xc8 > [  308.324711]  check_noncircular+0x12d/0x150 > [  308.324713]  __lock_acquire+0x119f/0x1fc0 > [  308.324715]  lock_acquire+0xa4/0x3b0 > [  308.324716]  ? rmap_walk_file+0x1c0/0x2f0 > [  308.324717]  ? __lock_acquire+0x394/0x1fc0 > [  308.324719]  down_read+0x2d/0x110 > [  308.324720]  ? rmap_walk_file+0x1c0/0x2f0 > [  308.324721]  rmap_walk_file+0x1c0/0x2f0 > [  308.324722]  page_referenced+0x133/0x150 > [  308.324724]  ? __page_set_anon_rmap+0x70/0x70 > [  308.324725]  ? page_get_anon_vma+0x190/0x190 > [  308.324726]  shrink_active_list+0x142/0x610 > [  308.324728]  balance_pgdat+0x229/0x620 > [  308.324730]  kswapd+0x200/0x470 > [  308.324731]  ? lockdep_hardirqs_on_prepare+0xf5/0x170 > [  308.324733]  ? finish_wait+0x80/0x80 > [  308.324734]  ? balance_pgdat+0x620/0x620 > [  308.324736]  kthread+0x11f/0x140 > [  308.324737]  ? kthread_create_worker_on_cpu+0x40/0x40 > [  308.324739]  ret_from_fork+0x1f/0x30 > > > > > > /Thomas > > > > > > > > > > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch