Re: [PATCH 6.0 19/20] mm/huge_memory: do not clobber swp_entry_t during THP split

[Greg Kroah-Hartman]

On Tue, Oct 25, 2022 at 08:11:44AM -0700, Hugh Dickins wrote:
> On Mon, 24 Oct 2022, Greg Kroah-Hartman wrote:
> > From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> > 
> > commit 71e2d666ef85d51834d658830f823560c402b8b6 upstream.
> > 
> > The following has been observed when running stressng mmap since commit
> > b653db77350c ("mm: Clear page->private when splitting or migrating a page")
> > 
> >    watchdog: BUG: soft lockup - CPU#75 stuck for 26s! [stress-ng:9546]
> >    CPU: 75 PID: 9546 Comm: stress-ng Tainted: G            E      6.0.0-revert-b653db77-fix+ #29 0357d79b60fb09775f678e4f3f64ef0579ad1374
> >    Hardware name: SGI.COM C2112-4GP3/X10DRT-P-Series, BIOS 2.0a 05/09/2016
> >    RIP: 0010:xas_descend+0x28/0x80
> >    Code: cc cc 0f b6 0e 48 8b 57 08 48 d3 ea 83 e2 3f 89 d0 48 83 c0 04 48 8b 44 c6 08 48 89 77 18 48 89 c1 83 e1 03 48 83 f9 02 75 08 <48> 3d fd 00 00 00 76 08 88 57 12 c3 cc cc cc cc 48 c1 e8 02 89 c2
> >    RSP: 0018:ffffbbf02a2236a8 EFLAGS: 00000246
> >    RAX: ffff9cab7d6a0002 RBX: ffffe04b0af88040 RCX: 0000000000000002
> >    RDX: 0000000000000030 RSI: ffff9cab60509b60 RDI: ffffbbf02a2236c0
> >    RBP: 0000000000000000 R08: ffff9cab60509b60 R09: ffffbbf02a2236c0
> >    R10: 0000000000000001 R11: ffffbbf02a223698 R12: 0000000000000000
> >    R13: ffff9cab4e28da80 R14: 0000000000039c01 R15: ffff9cab4e28da88
> >    FS:  00007fab89b85e40(0000) GS:ffff9cea3fcc0000(0000) knlGS:0000000000000000
> >    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >    CR2: 00007fab84e00000 CR3: 00000040b73a4003 CR4: 00000000003706e0
> >    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >    Call Trace:
> >     <TASK>
> >     xas_load+0x3a/0x50
> >     __filemap_get_folio+0x80/0x370
> >     ? put_swap_page+0x163/0x360
> >     pagecache_get_page+0x13/0x90
> >     __try_to_reclaim_swap+0x50/0x190
> >     scan_swap_map_slots+0x31e/0x670
> >     get_swap_pages+0x226/0x3c0
> >     folio_alloc_swap+0x1cc/0x240
> >     add_to_swap+0x14/0x70
> >     shrink_page_list+0x968/0xbc0
> >     reclaim_page_list+0x70/0xf0
> >     reclaim_pages+0xdd/0x120
> >     madvise_cold_or_pageout_pte_range+0x814/0xf30
> >     walk_pgd_range+0x637/0xa30
> >     __walk_page_range+0x142/0x170
> >     walk_page_range+0x146/0x170
> >     madvise_pageout+0xb7/0x280
> >     ? asm_common_interrupt+0x22/0x40
> >     madvise_vma_behavior+0x3b7/0xac0
> >     ? find_vma+0x4a/0x70
> >     ? find_vma+0x64/0x70
> >     ? madvise_vma_anon_name+0x40/0x40
> >     madvise_walk_vmas+0xa6/0x130
> >     do_madvise+0x2f4/0x360
> >     __x64_sys_madvise+0x26/0x30
> >     do_syscall_64+0x5b/0x80
> >     ? do_syscall_64+0x67/0x80
> >     ? syscall_exit_to_user_mode+0x17/0x40
> >     ? do_syscall_64+0x67/0x80
> >     ? syscall_exit_to_user_mode+0x17/0x40
> >     ? do_syscall_64+0x67/0x80
> >     ? do_syscall_64+0x67/0x80
> >     ? common_interrupt+0x8b/0xa0
> >     entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > 
> > The problem can be reproduced with the mmtests config
> > config-workload-stressng-mmap.  It does not always happen and when it
> > triggers is variable but it has happened on multiple machines.
> > 
> > The intent of commit b653db77350c patch was to avoid the case where
> > PG_private is clear but folio->private is not-NULL.  However, THP tail
> > pages uses page->private for "swp_entry_t if folio_test_swapcache()" as
> > stated in the documentation for struct folio.  This patch only clobbers
> > page->private for tail pages if the head page was not in swapcache and
> > warns once if page->private had an unexpected value.
> > 
> > Link: https://lkml.kernel.org/r/20221019134156.zjyyn5aownakvztf@xxxxxxxxxxxxxxxxxxx
> > Fixes: b653db77350c ("mm: Clear page->private when splitting or migrating a page")
> > Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> > Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> > Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> > Cc: Yang Shi <shy828301@xxxxxxxxx>
> > Cc: Brian Foster <bfoster@xxxxxxxxxx>
> > Cc: Dan Streetman <ddstreet@xxxxxxxx>
> > Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> > Cc: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
> > Cc: Seth Jennings <sjenning@xxxxxxxxxx>
> > Cc: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> 
> Greg, this patch from Mel is important,
> but introduces a warning which is giving Tvrtko trouble - see linux-mm
> https://lore.kernel.org/linux-mm/1596edbb-02ad-6bdf-51b8-15c2d2e08b76@xxxxxxxxxxxxxxx/
> 
> We already have the fix for the warning, it's making its way through the
> system, and is marked for stable, but it has not reached Linus's tree yet.
> 
> Please drop this 19/20 from 6.0.4, then I'll reply to this to let you know
> when the fix does reach Linus's tree - hopefully the two can go together
> in the next 6.0-stable.
> 
> I apologize for not writing yesterday: gmail had gathered together
> different threads with the same subject, I thought you and stable
> were Cc'ed on the linux-mm mail and you would immediately drop it
> yourself, but in fact you were not on that thread at all.

No worries, now dropped, thanks.

greg k-h