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Howlett" To: John Hsu =?utf-8?B?KOioseawuOe/sCk=?= Cc: Andrew Yang =?utf-8?B?KOaliuaZuuW8tyk=?= , "linux-kernel@vger.kernel.org" , Qun-wei Lin =?utf-8?B?KOael+e+pOW0tCk=?= , "linux-mm@kvack.org" , Chinwen Chang =?utf-8?B?KOW8temMpuaWhyk=?= , Casper Li =?utf-8?B?KOadjuS4reamrik=?= , Kuan-Ying Lee =?utf-8?B?KOadjuWGoOepjik=?= , "akpm@linux-foundation.org" , "yuzhao@google.com" , "maple-tree@lists.infradead.org" Subject: Re: [BUG] trigger BUG_ON in mas_store_prealloc when low memory Message-ID: <20230614155826.cxcpv33hs763gyrg@revolver> Mail-Followup-To: "Liam R. Howlett" , John Hsu =?utf-8?B?KOioseawuOe/sCk=?= , Andrew Yang =?utf-8?B?KOaliuaZuuW8tyk=?= , "linux-kernel@vger.kernel.org" , Qun-wei Lin =?utf-8?B?KOael+e+pOW0tCk=?= , "linux-mm@kvack.org" , Chinwen Chang =?utf-8?B?KOW8temMpuaWhyk=?= , Casper Li =?utf-8?B?KOadjuS4reamrik=?= , Kuan-Ying Lee =?utf-8?B?KOadjuWGoOepjik=?= , "akpm@linux-foundation.org" , "yuzhao@google.com" , "maple-tree@lists.infradead.org" References: <9cb8c599b1d7f9c1c300d1a334d5eb70ec4d7357.camel@mediatek.com> <20230613141114.bwbnqsdazqbmyj3u@revolver> <3b14df2fc2a7f18fe12f87a27574b7d40f2899ba.camel@mediatek.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: <3b14df2fc2a7f18fe12f87a27574b7d40f2899ba.camel@mediatek.com> User-Agent: NeoMutt/20220429 X-ClientProxiedBy: YT4PR01CA0374.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:fd::8) To SN6PR10MB3022.namprd10.prod.outlook.com (2603:10b6:805:d8::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email 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 vAo/jfzU 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Sorry, your email response with top posting is hard to follow so I will do my best to answer your questions. >=20 >=20 >=20 > version 6.1 or 6.1.x? Which exact version (git id or version number) >=20 > Our environment is kernel-6.1.25-mainline-android14-5-gdea04bf2c398d. Okay, I can have a look at 6.1.25 then. >=20 >=20 > This BUG_ON() is necessary since this function should _never_ run out of >=20 > memory; this function does not return an error code. mas_preallocate() >=20 > should have gotten you the memory necessary (or returned an -ENOMEM) >=20 > prior to the call to mas_store_prealloc(), so this is probably an >=20 > internal tree problem. >=20 > There is a tree operation being performed here. mprotect is merging a >=20 > vma by the looks of the call stack. Why do you think no tree operation >=20 > is necessary? >=20 > As you mentioned, mas_preallocate() should allocate enough node, but ther= e is such functions mas_node_count() in mas_store_prealloc(). > In mas_node_count() checks whether the *mas* has enough nodes, and alloca= te 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. > 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_no= de_count()? We check for the above reason. >=20 > 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. >=20 > 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. 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 e= nough available memory. > Is there any concern for this design? This has been addressed above, but let me know if I missed anything here. >=20 >=20 > I see this is arm64. Do you have a reproducer? If you don't have a >=20 > reproducer, I can try stress-ng on amr64 to simulate your workload using >=20 > mprotect, but I need to know the exact kernel version as this issue may >=20 > have been fixed in a later stable release. >=20 > It is offen occur under low memory condiction. Maybe you can try stress-n= g on arm64 under high memory stress(e.g. reserved lots of memory). Okay, I will try arm64 with v6.1.25. ... > > following are the backtrace: >=20 > > mas_store_prealloc+0x23c/0x484 >=20 > > vma_mas_store+0xe4/0x2d0 >=20 > > __vma_adjust+0xab0/0x1470 >=20 > > vma_merge+0x5b8/0x5d4 >=20 > > mprotect_fixup+0x1f4/0x478 >=20 > > __arm64_sys_mprotect+0x6b0/0x8f0 >=20 > > invoke_syscall+0x84/0x264 >=20 > > el0_svc_common+0x118/0x1f0 >=20 > > do_el0_svc+0x5c/0x184 >=20 > > el0_svc+0x38/0x98 >=20 Thanks, Liam