From: Rongwei Wang <rongwei.wang@linux.alibaba.com>
To: Yang Shi <shy828301@gmail.com>
Cc: Linux MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
cfijalkovich@google.com, song@kernel.org,
william.kucharski@oracle.com, Hugh Dickins <hughd@google.com>,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH 1/2] mm, thp: check page mapping when truncating page cache
Date: Wed, 8 Sep 2021 10:35:41 +0800 [thread overview]
Message-ID: <38AF4DC8-5E6F-4568-B2E3-0434BD847BC9@linux.alibaba.com> (raw)
In-Reply-To: <CAHbLzkrx2scQa29WU6KD3gCNfRtwoyORcAzj2_nCZh1aaSdW8g@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 8833 bytes --]
> On Sep 8, 2021, at 2:08 AM, Yang Shi <shy828301@gmail.com> wrote:
>
> On Mon, Sep 6, 2021 at 5:12 AM Rongwei Wang
> <rongwei.wang@linux.alibaba.com <mailto:rongwei.wang@linux.alibaba.com>> wrote:
>>
>> Transparent huge page has supported read-only non-shmem files. The file-
>> backed THP is collapsed by khugepaged and truncated when written (for
>> shared libraries).
>>
>> However, there is race in two possible places.
>>
>> 1) multiple writers truncate the same page cache concurrently;
>> 2) collapse_file rolls back when writer truncates the page cache;
>>
>> In both cases, subpage(s) of file THP can be revealed by find_get_entry
>> in truncate_inode_pages_range, which will trigger PageTail BUG_ON in
>> truncate_inode_page, as follows.
>>
>> [40326.247034] page:000000009e420ff2 refcount:1 mapcount:0 mapping:0000000000000000 index:0x7ff pfn:0x50c3ff
>> [40326.247041] head:0000000075ff816d order:9 compound_mapcount:0 compound_pincount:0
>> [40326.247046] flags: 0x37fffe0000010815(locked|uptodate|lru|arch_1|head)
>> [40326.247051] raw: 37fffe0000000000 fffffe0013108001 dead000000000122 dead000000000400
>> [40326.247053] raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
>> [40326.247055] head: 37fffe0000010815 fffffe001066bd48 ffff000404183c20 0000000000000000
>> [40326.247057] head: 0000000000000600 0000000000000000 00000001ffffffff ffff000c0345a000
>> [40326.247058] page dumped because: VM_BUG_ON_PAGE(PageTail(page))
>> [40326.247077] ------------[ cut here ]------------
>> [40326.247080] kernel BUG at mm/truncate.c:213!
>> [40326.280581] Internal error: Oops - BUG: 0 [#1] SMP
>> [40326.281077] Modules linked in: xfs(E) libcrc32c(E) rfkill(E) aes_ce_blk(E) crypto_simd(E) cryptd(E) aes_ce_cipher(E) crct10dif_ce(E) ghash_ce(E) sha1_ce(E) uio_pdrv_genirq(E) uio(E) nfsd(E) vfat(E) fat(E) auth_rpcgss(E) nfs_acl(E) lockd(E) grace(E) sunrpc(E) sch_fq_codel(E) ip_tables(E) ext4(E) mbcache(E) jbd2(E) virtio_net(E) net_failover(E) virtio_blk(E) failover(E) sha2_ce(E) sha256_arm64(E) virtio_mmio(E) virtio_pci(E) virtio_ring(E) virtio(E)
>> [40326.285130] CPU: 14 PID: 11394 Comm: check_madvise_d Kdump: loaded Tainted: G W E 5.10.46-hugetext+ #55
>> [40326.286202] Hardware name: Alibaba Cloud Alibaba Cloud ECS, BIOS 0.0.0 02/06/2015
>> [40326.286968] pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--)
>> [40326.287584] pc : truncate_inode_page+0x64/0x70
>> [40326.288040] lr : truncate_inode_page+0x64/0x70
>> [40326.288498] sp : ffff80001b60b900
>> [40326.288837] x29: ffff80001b60b900 x28: 00000000000007ff
>> [40326.289377] x27: ffff80001b60b9a0 x26: 0000000000000000
>> [40326.289943] x25: 000000000000000f x24: ffff80001b60b9a0
>> [40326.290485] x23: ffff80001b60ba18 x22: ffff0001e0999ea8
>> [40326.291027] x21: ffff0000c21db300 x20: ffffffffffffffff
>> [40326.291566] x19: fffffe001310ffc0 x18: 0000000000000020
>> [40326.292106] x17: 0000000000000000 x16: 0000000000000000
>> [40326.292655] x15: ffff0000c21db960 x14: 3030306666666620
>> [40326.293197] x13: 6666666666666666 x12: 3130303030303030
>> [40326.293746] x11: ffff8000117b69b8 x10: 00000000ffff8000
>> [40326.294313] x9 : ffff80001012690c x8 : 0000000000000000
>> [40326.294851] x7 : ffff8000114f69b8 x6 : 0000000000017ffd
>> [40326.295392] x5 : ffff0007fffbcbc8 x4 : ffff80001b60b5c0
>> [40326.295942] x3 : 0000000000000001 x2 : 0000000000000000
>> [40326.296497] x1 : 0000000000000000 x0 : 0000000000000000
>> [40326.297047] Call trace:
>> [40326.297304] truncate_inode_page+0x64/0x70
>> [40326.297724] truncate_inode_pages_range+0x550/0x7e4
>> [40326.298251] truncate_pagecache+0x58/0x80
>> [40326.298662] do_dentry_open+0x1e4/0x3c0
>> [40326.299052] vfs_open+0x38/0x44
>> [40326.299377] do_open+0x1f0/0x310
>> [40326.299709] path_openat+0x114/0x1dc
>> [40326.300077] do_filp_open+0x84/0x134
>> [40326.300444] do_sys_openat2+0xbc/0x164
>> [40326.300825] __arm64_sys_openat+0x74/0xc0
>> [40326.301236] el0_svc_common.constprop.0+0x88/0x220
>> [40326.301723] do_el0_svc+0x30/0xa0
>> [40326.302089] el0_svc+0x20/0x30
>> [40326.302404] el0_sync_handler+0x1a4/0x1b0
>> [40326.302814] el0_sync+0x180/0x1c0
>> [40326.303157] Code: aa0103e0 900061e1 910ec021 9400d300 (d4210000)
>> [40326.303775] ---[ end trace f70cdb42cb7c2d42 ]---
>> [40326.304244] Kernel panic - not syncing: Oops - BUG: Fatal exception
>>
>> This checks the page mapping and retries when subpage of file THP is
>> found, in truncate_inode_pages_range.
>>
>> Fixes: eb6ecbed0aa2 ("mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs")
>> Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
>> Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com>
>> ---
>> mm/filemap.c | 7 ++++++-
>> mm/truncate.c | 17 ++++++++++++++++-
>> 2 files changed, 22 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index dae481293..a3af2ec 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -2093,7 +2093,6 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
>> if (!xa_is_value(page)) {
>> if (page->index < start)
>> goto put;
>> - VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
>> if (page->index + thp_nr_pages(page) - 1 > end)
>> goto put;
>> if (!trylock_page(page))
>> @@ -2102,6 +2101,12 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
>> goto unlock;
>> VM_BUG_ON_PAGE(!thp_contains(page, xas.xa_index),
>> page);
>> + /*
>> + * We can find and get head page of file THP with
>> + * non-head index. The head page should have already
>> + * be truncated with page->mapping reset to NULL.
>> + */
>> + VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
>> }
>> indices[pvec->nr] = xas.xa_index;
>> if (!pagevec_add(pvec, page))
>> diff --git a/mm/truncate.c b/mm/truncate.c
>> index 714eaf1..8c59c00 100644
>> --- a/mm/truncate.c
>> +++ b/mm/truncate.c
>> @@ -319,7 +319,8 @@ void truncate_inode_pages_range(struct address_space *mapping,
>> index = start;
>> while (index < end && find_lock_entries(mapping, index, end - 1,
>> &pvec, indices)) {
>> - index = indices[pagevec_count(&pvec) - 1] + 1;
>> + index = indices[pagevec_count(&pvec) - 1] +
>> + thp_nr_pages(pvec.pages[pagevec_count(&pvec) - 1]);
>
> I don't quite get what this change is doing for. IIUC
> find_lock_entries() already handles index advance correctly. If
> truncate range is partial THP, it will be handled in the second pass.
Yes, agree.
> AFAICT, the problem is why the THP is not split if it will get
Yes, agree.
This change is not necessary, but nice to have. Because find_lock_entries()
return only head page if any, and it is better to advance the index by thp_nr_pages(), instead of 1.
If you think it introduces unnecessary complexity, I don't mind discarding this change.
> partially truncated. Did I miss something?
>
>
>> truncate_exceptional_pvec_entries(mapping, &pvec, indices);
>> for (i = 0; i < pagevec_count(&pvec); i++)
>> truncate_cleanup_page(pvec.pages[i]);
>> @@ -391,6 +392,20 @@ void truncate_inode_pages_range(struct address_space *mapping,
>> if (xa_is_value(page))
>> continue;
>>
>> + /*
>> + * Already truncated? We can find and get subpage
>> + * of file THP, of which the head page is truncated.
>> + *
>> + * In addition, another race will be avoided, where
>> + * collapse_file rolls back when writer truncates the
>> + * page cache.
>> + */
>> + if (page_mapping(page) != mapping) {
>> + /* Restart to make sure all gone */
>> + index = start - 1;
>> + continue;
>> + }
>> +
>> lock_page(page);
>> WARN_ON(page_to_index(page) != index);
>> wait_on_page_writeback(page);
>> —
>> 1.8.3.1
Thanks,
Rongwei Wang
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next prev parent reply other threads:[~2021-09-08 2:41 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-06 12:11 [PATCH 0/2] mm, thp: fix file-backed THP race in collapse_file Rongwei Wang
2021-09-06 12:11 ` [PATCH 1/2] mm, thp: check page mapping when truncating page cache Rongwei Wang
2021-09-07 2:49 ` Yu Xu
2021-09-07 18:08 ` Yang Shi
2021-09-08 2:35 ` Rongwei Wang [this message]
2021-09-08 21:48 ` Yang Shi
2021-09-09 1:25 ` Rongwei Wang
2021-09-13 14:49 ` [mm, thp] 20753096b6: BUG:unable_to_handle_page_fault_for_address kernel test robot
2021-09-06 12:12 ` [PATCH 2/2] mm, thp: bail out early in collapse_file for writeback page Rongwei Wang
2021-09-07 16:56 ` Yang Shi
2021-09-08 2:16 ` Rongwei Wang
2021-09-08 21:51 ` Yang Shi
2021-09-09 1:33 ` Rongwei Wang
2021-09-22 7:06 ` [PATCH v2 0/2] mm, thp: fix file-backed THP race in collapse_file and truncate pagecache Rongwei Wang
2021-09-22 7:06 ` [PATCH v2 1/2] mm, thp: check page mapping when truncating page cache Rongwei Wang
2021-09-22 11:37 ` Matthew Wilcox
2021-09-22 17:04 ` Rongwei Wang
2021-09-24 2:43 ` Andrew Morton
2021-09-24 3:08 ` Yang Shi
2021-09-24 3:35 ` Rongwei Wang
2021-09-24 7:12 ` Rongwei Wang
2021-09-27 22:24 ` Song Liu
2021-09-28 12:06 ` Matthew Wilcox
2021-09-28 16:59 ` Song Liu
2021-09-28 16:20 ` Rongwei Wang
2021-09-29 7:14 ` Song Liu
2021-09-29 7:50 ` Rongwei Wang
2021-09-29 16:59 ` Song Liu
2021-09-29 17:55 ` Matthew Wilcox
2021-09-29 23:41 ` Song Liu
2021-09-30 0:00 ` Matthew Wilcox
2021-09-30 0:41 ` Song Liu
2021-09-30 2:14 ` Rongwei Wang
2021-10-04 17:26 ` Rongwei Wang
2021-10-04 19:05 ` Matthew Wilcox
2021-10-05 1:58 ` Rongwei Wang
2021-10-04 20:26 ` Song Liu
2021-10-05 2:58 ` Hugh Dickins
2021-10-05 3:07 ` Matthew Wilcox
2021-10-05 9:03 ` Rongwei Wang
2021-09-30 1:54 ` Rongwei Wang
2021-09-30 3:26 ` Song Liu
2021-09-30 5:24 ` Hugh Dickins
2021-09-30 15:28 ` Matthew Wilcox
2021-09-30 16:49 ` Hugh Dickins
2021-09-30 17:39 ` Yang Shi
2021-10-02 17:08 ` Matthew Wilcox
2021-10-04 18:28 ` Yang Shi
2021-10-04 19:31 ` Matthew Wilcox
2021-10-05 2:26 ` Hugh Dickins
2021-10-02 2:22 ` Rongwei Wang
2021-09-22 7:06 ` [PATCH v2 2/2] mm, thp: bail out early in collapse_file for writeback page Rongwei Wang
2021-10-06 2:18 ` [PATCH v3 v3 0/2] mm, thp: fix file-backed THP race in collapse_file and truncate pagecache Rongwei Wang
2021-10-06 2:18 ` [PATCH v3 v3 1/2] mm, thp: lock filemap when truncating page cache Rongwei Wang
2021-10-06 2:18 ` [PATCH v3 v3 2/2] mm, thp: bail out early in collapse_file for writeback page Rongwei Wang
2021-10-06 2:41 ` Matthew Wilcox
2021-10-06 8:39 ` Rongwei Wang
2021-10-06 17:58 ` Yang Shi
2021-10-11 2:22 ` [PATCH v4 0/2] mm, thp: fix file-backed THP race in collapse_file and truncate pagecache Rongwei Wang
2021-10-11 2:22 ` [PATCH v4 1/2] mm, thp: lock filemap when truncating page cache Rongwei Wang
2021-10-13 7:55 ` Rongwei Wang
2021-10-11 2:22 ` [PATCH v4 2/2] mm, thp: bail out early in collapse_file for writeback page Rongwei Wang
2021-10-11 3:08 ` Matthew Wilcox
2021-10-11 3:22 ` Rongwei Wang
2021-10-11 5:08 ` [PATCH v4 RESEND " Rongwei Wang
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