Re: v5.1-rc5 s390x WARNING

[Vlastimil Babka <vbabka@suse.cz>]

On 4/17/19 10:35 AM, Li Wang wrote:
> Hi there,
> 
> I catched this warning on v5.1-rc5(s390x). It was trggiered in fork & malloc & memset stress test, but the reproduced rate is very low. I'm working on find a stable reproducer for it. 
> 
> Anyone can have a look first?
> 
> [ 1422.124060] WARNING: CPU: 0 PID: 9783 at mm/page_alloc.c:3777 __alloc_pages_irect_compact+0x182/0x190

This means compaction was either skipped or deferred, yet it captured a
page. We have some registers with value 1 and 2, which is
COMPACT_SKIPPED and COMPACT_DEFERRED, so it could be one of those.
Probably COMPACT_SKIPPED. I think a race is possible:

- compact_zone_order() sets up current->capture_control
- compact_zone() calls compaction_suitable() which returns
COMPACT_SKIPPED, so it also returns
- interrupt comes and its processing happens to free a page that forms
high-order page, since 'current' isn't changed during interrupt (IIRC?)
the capture_control is still active and the page is captured
- compact_zone_order() does *capture = capc.page

What do you think, Mel, does it look plausible? Not sure whether we want
to try avoiding this scenario, or just remove the warning and be
grateful for the successful capture :)

> [ 1422.124065] Modules linked in: rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver 
>  nfs lockd grace fscache sunrpc pkey ghash_s390 prng xts aes_s390 des_s390 des_g 
> eneric sha512_s390 zcrypt_cex4 zcrypt vmur binfmt_misc ip_tables xfs libcrc32c d 
> asd_fba_mod qeth_l2 dasd_eckd_mod dasd_mod qeth qdio lcs ctcm ccwgroup fsm dm_mi 
> rror dm_region_hash dm_log dm_mod                                                
> [ 1422.124086] CPU: 0 PID: 9783 Comm: copy.sh Kdump: loaded Not tainted 5.1.0-rc 5 #1                                                                             
> [ 1422.124089] Hardware name: IBM 2827 H43 400 (z/VM 6.4.0)                      
> [ 1422.124092] Krnl PSW : 0704e00180000000 00000000002779ba (__alloc_pages_direct_compact+0x182/0x190)                                                           
> [ 1422.124096]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI: 0 EA:3                                                                           
> [ 1422.124100] Krnl GPRS: 0000000000000000 000003e00226fc24 000003d081bdf200 000 0000000000001                                                                    
> [ 1422.124103]            000000000027789a 0000000000000000 0000000000000001 000 000000006ee03                                                                    
> [ 1422.124107]            000003e00226fc28 0000000000000cc0 0000000000000240 000 0000000000002                                                                    
> [ 1422.124156]            0000000000400000 0000000000753cb0 000000000027789a 000 003e00226fa28                                                                    
> [ 1422.124163] Krnl Code: 00000000002779ac: e320f0a80002        ltg     %r2,168( %r15)                                                                            
> [ 1422.124163]            00000000002779b2: a784fff4            brc     8,27799a                                                                                  
> [ 1422.124163]           #00000000002779b6: a7f40001            brc     15,2779b 8                                                                                
> [ 1422.124163]           >00000000002779ba: a7290000            lghi    %r2,0    
> [ 1422.124163]            00000000002779be: a7f4fff0            brc     15,27799 e                                                                                
> [ 1422.124163]            00000000002779c2: 0707                bcr     0,%r7    
> [ 1422.124163]            00000000002779c4: 0707                bcr     0,%r7    
> [ 1422.124163]            00000000002779c6: 0707                bcr     0,%r7    
> [ 1422.124194] Call Trace:                                                       
> [ 1422.124196] ([<000000000027789a>] __alloc_pages_direct_compact+0x62/0x190)    
> [ 1422.124198]  [<0000000000278618>] __alloc_pages_nodemask+0x728/0x1148         
> [ 1422.124201]  [<0000000000126bb2>] crst_table_alloc+0x32/0x68                  
> [ 1422.124203]  [<0000000000135888>] mm_init+0x118/0x308                         
> [ 1422.124204]  [<0000000000137e60>] copy_process.part.49+0x1820/0x1d90          
> [ 1422.124205]  [<000000000013865c>] _do_fork+0x114/0x3b8                        
> [ 1422.124206]  [<0000000000138aa4>] __s390x_sys_clone+0x44/0x58                 
> [ 1422.124210]  [<0000000000739a90>] system_call+0x288/0x2a8                     
> [ 1422.124210] Last Breaking-Event-Address:                                      
> [ 1422.124212]  [<00000000002779b6>] __alloc_pages_direct_compact+0x17e/0x190    
> [ 1422.124213] ---[ end trace 36649eaa36968eaa ]---                              
> 
> -- 
> Regards,
> Li Wang