Hi Gao Xiang,
On 10/30/20 2:47 PM, Gao Xiang wrote:
Hi Vladimir,
On Fri, Oct 30, 2020 at 02:20:31PM +0200, Vladimir Zapolskiy wrote:
Hello Gao Xiang,
On 10/22/20 5:57 PM, Gao Xiang via Linux-erofs wrote:
From: Gao Xiang hsiangkao@redhat.com
pcluster should be only set up for all managed pages instead of temporary pages. Since it currently uses page->mapping to identify, the impact is minor for now.
Fixes: 5ddcee1f3a1c ("erofs: get rid of __stagingpage_alloc helper") Cc: stable@vger.kernel.org # 5.5+ Signed-off-by: Gao Xiang hsiangkao@redhat.com
I was looking exactly at this problem recently, my change is one-to-one to your fix, thus I can provide a tag:
Tested-by: Vladimir Zapolskiy vladimir@tuxera.com
Many thanks for confirming this! I found this when I was killing magical stagingpage page->mapping, it's somewhat late :-)
sure, for me it was an exciting immersion into the filesystem code :)
The fixed problem is minor, but the kernel log becomes polluted, if a page allocation debug option is enabled:
% md5sum ~/erofs/testfile BUG: Bad page state in process kworker/u9:0 pfn:687de page:0000000057b8bcb4 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x687de flags: 0x4000000000002000(private) raw: 4000000000002000 dead000000000100 dead000000000122 0000000000000000 raw: 0000000000000000 ffff888066758690 00000000ffffffff 0000000000000000 page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set Modules linked in: CPU: 1 PID: 602 Comm: kworker/u9:0 Not tainted 5.9.1 #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014 Workqueue: erofs_unzipd z_erofs_decompressqueue_work Call Trace: dump_stack+0x84/0xba bad_page.cold+0xac/0xb1 check_free_page_bad+0xb0/0xc0 free_pcp_prepare+0x2c8/0x2d0 free_unref_page+0x18/0xf0 put_pages_list+0x11a/0x120 z_erofs_decompressqueue_work+0xc9/0x110 ? z_erofs_decompress_pcluster.isra.0+0xf10/0xf10 ? read_word_at_a_time+0x12/0x20 ? strscpy+0xc7/0x1a0 process_one_work+0x30c/0x730 worker_thread+0x91/0x640 ? __kasan_check_read+0x11/0x20 ? rescuer_thread+0x8a0/0x8a0 kthread+0x1dd/0x200 ? kthread_unpark+0xa0/0xa0 ret_from_fork+0x1f/0x30 Disabling lock debugging due to kernel taintYeah, I can make a pull-request to Linus if you need this to be in master now, or I can post it for v5.11-rc1 since 5.4 LTS isn't effected (and it would be only a print problem with debugging option.)
As for myself I don't utterly need this fix on the master branch ASAP, however it might be reasonable to get it included right into the next v5.10 release, because I believe it'll be an LTS. Eventually it's up to you to make a decision, from my side I won't urge you, the fixed issue is obviously a non-critical one.
Thank you for the original fix and taking my opinion into consideration :)
-- Best wishes, Vladimir