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Tue, 25 Feb 2025 08:12:54 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id UUOTHIZ7vWfReQAAD6G6ig (envelope-from ); Tue, 25 Feb 2025 08:12:54 +0000 Message-ID: <1c31d364-291b-4284-84b0-f71afcdd0c66@suse.cz> Date: Tue, 25 Feb 2025 09:12:54 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/page_alloc: Fix uninitialized variable Content-Language: en-US To: Andrew Morton , 76824143@qq.com Cc: linux-mm@kvack.org, Hao Zhang , syzbot+0cfd5e38e96a5596f2b6@syzkaller.appspotmail.com, Michal Hocko , Mel Gorman References: <20250224212911.ba73c0501814c554a9a8ecf6@linux-foundation.org> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: <20250224212911.ba73c0501814c554a9a8ecf6@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 88CB31C000A X-Stat-Signature: m8h7auwo69pni8a7rmumoxyiq5gcu9t8 X-Rspam-User: X-HE-Tag: 1740471176-661235 X-HE-Meta: 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 AD0cW0Rw 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/25/25 06:29, Andrew Morton wrote: > On Tue, 25 Feb 2025 10:20:34 +0800 76824143@qq.com wrote: > >> From: Hao Zhang >> >> The variable "compact_result" is not initialized in function >> __alloc_pages_direct_compact if order is zero. > > Thanks, this could be rather old. Or did we do something recently to > trigger this? I don't think so, perhaps KMSAN improved or something? Note it catches the passing of uninitalized value to should_compact_retry() (according to the reported line 4416), but when compact_result is not initialized, order is 0 and in that case should_compact_retry() does not even look at compact_result. So it was probably harmless all the time, modulo "undefined behavior" I guess. >> If order is zero, initialize "compact_result" to COMPACT_SKIPPED. >> >> BUG: KMSAN: uninit-value in __alloc_pages_slowpath+0xee8/0x16c0 mm/page_alloc.c:4416 >> __alloc_pages_slowpath+0xee8/0x16c0 mm/page_alloc.c:4416 >> __alloc_frozen_pages_noprof+0xa4c/0xe00 mm/page_alloc.c:4752 >> alloc_pages_mpol+0x4cd/0x890 mm/mempolicy.c:2270 >> alloc_frozen_pages_noprof mm/mempolicy.c:2341 [inline] >> alloc_pages_noprof mm/mempolicy.c:2361 [inline] >> folio_alloc_noprof+0x1dc/0x350 mm/mempolicy.c:2371 >> filemap_alloc_folio_noprof+0xa6/0x440 mm/filemap.c:1019 >> __filemap_get_folio+0xb9a/0x1840 mm/filemap.c:1970 >> grow_dev_folio fs/buffer.c:1039 [inline] >> grow_buffers fs/buffer.c:1105 [inline] >> __getblk_slow fs/buffer.c:1131 [inline] >> bdev_getblk+0x2c9/0xab0 fs/buffer.c:1431 >> getblk_unmovable include/linux/buffer_head.h:369 [inline] >> ext4_getblk+0x3b7/0xe50 fs/ext4/inode.c:864 >> ext4_bread_batch+0x9f/0x7d0 fs/ext4/inode.c:933 >> __ext4_find_entry+0x1ebb/0x36c0 fs/ext4/namei.c:1627 >> ext4_lookup_entry fs/ext4/namei.c:1729 [inline] >> ext4_lookup+0x189/0xb40 fs/ext4/namei.c:1797 >> __lookup_slow+0x538/0x710 fs/namei.c:1793 >> lookup_slow+0x6a/0xd0 fs/namei.c:1810 >> walk_component fs/namei.c:2114 [inline] >> link_path_walk+0xf29/0x1420 fs/namei.c:2479 >> path_openat+0x30f/0x6250 fs/namei.c:3985 >> do_filp_open+0x268/0x600 fs/namei.c:4016 >> do_sys_openat2+0x1bf/0x2f0 fs/open.c:1428 >> do_sys_open fs/open.c:1443 [inline] >> __do_sys_openat fs/open.c:1459 [inline] >> __se_sys_openat fs/open.c:1454 [inline] >> __x64_sys_openat+0x2a1/0x310 fs/open.c:1454 >> x64_sys_call+0x36f5/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:258 >> do_syscall_x64 arch/x86/entry/common.c:52 [inline] >> do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83 >> entry_SYSCALL_64_after_hwframe+0x77/0x7f >> >> Local variable compact_result created at: >> __alloc_pages_slowpath+0x66/0x16c0 mm/page_alloc.c:4218 >> __alloc_frozen_pages_noprof+0xa4c/0xe00 mm/page_alloc.c:4752 >> >> Reported-by: syzbot+0cfd5e38e96a5596f2b6@syzkaller.appspotmail.com >> Closes: https://syzkaller.appspot.com/bug?extid=0cfd5e38e96a5596f2b6 >> Signed-off-by: Hao Zhang Reviewed-by: Vlastimil Babka >> --- >> mm/page_alloc.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 579789600a3c..7f0136a404b5 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -3675,8 +3675,10 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, >> unsigned long pflags; >> unsigned int noreclaim_flag; >> >> - if (!order) >> + if (!order) { >> + *compact_result = COMPACT_SKIPPED; >> return NULL; >> + } >> > > Maybe. Or maybe __alloc_pages_slowpath() shouldn't be passing an > uninitialized compact_result into should_compact_retry()? I think this solution is fine. We could init it from outside to a safe value, but then if we again forget to set it in __alloc_pages_direct_compact() in some corner case, will that value be correct? Better if KMSAN tells us again I think. >