On Wed, 2023-06-14 at 11:58 -0400, Liam R. Howlett wrote: > > External email : Please do not click links or open attachments until > you have verified the sender or the content. > * John Hsu (許永翰) <John.Hsu@xxxxxxxxxxxx> [230614 03:06]: > > Hi Liam, thanks for your reply. > > Sorry, your email response with top posting is hard to follow so I > will > do my best to answer your questions. Sorry for the wrong format.... > > > > > > > > version 6.1 or 6.1.x? Which exact version (git id or version > number) > > > > Our environment is kernel-6.1.25-mainline-android14-5- > gdea04bf2c398d. > > Okay, I can have a look at 6.1.25 then. OK, thanks. > > > > > > This BUG_ON() is necessary since this function should _never_ run > out of > > > > memory; this function does not return an error code. > mas_preallocate() > > > > should have gotten you the memory necessary (or returned an > -ENOMEM) > > > > prior to the call to mas_store_prealloc(), so this is probably an > > > > internal tree problem. > > > > There is a tree operation being performed here. mprotect is > merging a > > > > vma by the looks of the call stack. Why do you think no tree > operation > > > > is necessary? > > > > As you mentioned, mas_preallocate() should allocate enough node, > but there is such functions mas_node_count() in mas_store_prealloc(). > > In mas_node_count() checks whether the *mas* has enough nodes, and > allocate memory for node if there was no enough nodes in mas. > > Right, we call mas_node_count() so that both code paths are used for > preallocations and regular mas_store()/mas_store_gfp(). It shouldn't > take a significant amount of time to verify there is enough nodes. Yap..., it didn't take a significant amount of time to verify whether there is enough nodes. The problem is why the flow in mas_node_count will alloc nodes if there was no enough nodes in mas? > > I think that if mas_preallocate() allocate enough node, why we > check the node count and allocate nodes if there was no enough nodes > in mas in mas_node_count()? > > We check for the above reason. > OK..., this is one of the root cause of this BUG. > > > > We have seen that there may be some maple_tree operations in > merge_vma... > > If merge_vma() does anything, then there was an operation to the > maple > tree. > > > > > Moreover, would maple_tree provides an API for assigning user's gfp > flag for allocating node? > > mas_preallocate() and mas_store_gfp() has gfp flags as an > argument. In > your call stack, it will be called in __vma_adjust() as such: > > if (mas_preallocate(&mas, vma, GFP_KERNEL)) > return -ENOMEM; > > line 715 in v6.1.25 > > > In rb_tree, we allocate vma_area_struct (rb_node is in this > struct.) with GFP_KERNEL, and maple_tree allocate node with > GFP_NOWAIT and __GFP_NOWARN. > > We use GFP_KERNEL as I explained above for the VMA tree. Got it! But the mas_node_count() always use GFP_NOWAIT and __GFP_NOWARN in inserting tree flow. Do you consider the performance of maintaining the structure of maple_tree? > It also will drop the lock and retry with GFP_KERNEL on failure > when not using the external lock. The mmap_lock is configured as an > external lock. > > > Allocation will not wait for reclaiming and compacting when there > is no enough available memory. > > Is there any concern for this design? > > This has been addressed above, but let me know if I missed anything > here. > I think that the mas_node_count() has higher rate of triggering BUG_ON() when allocating nodes with GFP_NOWAIT and __GFP_NOWARN. If mas_node_count() use GFP_KERNEL as mas_preallocate() in the mmap.c, the allocation fail rate may be lower than use GFP_NOWAIT. > > > > > > I see this is arm64. Do you have a reproducer? If you don't have > a > > > > reproducer, I can try stress-ng on amr64 to simulate your workload > using > > > > mprotect, but I need to know the exact kernel version as this issue > may > > > > have been fixed in a later stable release. > > > > It is offen occur under low memory condiction. Maybe you can try > stress-ng on arm64 under high memory stress(e.g. reserved lots of > memory). > > Okay, I will try arm64 with v6.1.25. OK, thanks. > ... > > > following are the backtrace: > > > > > mas_store_prealloc+0x23c/0x484 > > > > > vma_mas_store+0xe4/0x2d0 > > > > > __vma_adjust+0xab0/0x1470 > > > > > vma_merge+0x5b8/0x5d4 > > > > > mprotect_fixup+0x1f4/0x478 > > > > > __arm64_sys_mprotect+0x6b0/0x8f0 > > > > > invoke_syscall+0x84/0x264 > > > > > el0_svc_common+0x118/0x1f0 > > > > > do_el0_svc+0x5c/0x184 > > > > > el0_svc+0x38/0x98 > > > > Thanks, > Liam BRs, John Hsu
