| Message ID | 20210906121200.57905-3-rongwei.wang@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm, thp: fix file-backed THP race in collapse_file | expand |
On Mon, Sep 6, 2021 at 5:12 AM Rongwei Wang <rongwei.wang@linux.alibaba.com> wrote: > > Currently collapse_file does not explicitly check PG_writeback, instead, > page_has_private and try_to_release_page are used to filter writeback > pages. This does not work for xfs with blocksize equal to or larger I'm not quite sure if using try_to_release() to check the writeback flag is on purpose or not, but it should be better to check the flag more explicitly. > than pagesize, because in such case xfs has no page->private. > > This makes collapse_file bail out early for writeback page. Otherwise, > xfs end_page_writeback will panic as follows. > > [ 6411.448211] page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:ffff0003f88c86a8 index:0x0 pfn:0x84ef32 > [ 6411.448304] aops:xfs_address_space_operations [xfs] ino:30000b7 dentry name:"libtest.so" > [ 6411.448312] flags: 0x57fffe0000008027(locked|referenced|uptodate|active|writeback) > [ 6411.448317] raw: 57fffe0000008027 ffff80001b48bc28 ffff80001b48bc28 ffff0003f88c86a8 > [ 6411.448321] raw: 0000000000000000 0000000000000000 00000000ffffffff ffff0000c3e9a000 > [ 6411.448324] page dumped because: VM_BUG_ON_PAGE(((unsigned int) page_ref_count(page) + 127u <= 127u)) > [ 6411.448327] page->mem_cgroup:ffff0000c3e9a000 > [ 6411.448340] ------------[ cut here ]------------ > [ 6411.448343] kernel BUG at include/linux/mm.h:1212! > [ 6411.449288] Internal error: Oops - BUG: 0 [#1] SMP > [ 6411.449786] Modules linked in: > [ 6411.449790] BUG: Bad page state in process khugepaged pfn:84ef32 > [ 6411.450143] xfs(E) > [ 6411.450459] page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:0 index:0x0 pfn:0x84ef32 > [ 6411.451361] 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) vfat(E) nfsd(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) > [ 6411.451387] CPU: 25 PID: 0 Comm: swapper/25 Kdump: loaded Tainted: G W E > [ 6411.451389] pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) > [ 6411.451393] pc : end_page_writeback+0x1c0/0x214 > [ 6411.451394] lr : end_page_writeback+0x1c0/0x214 > [ 6411.451395] sp : ffff800011ce3cc0 > [ 6411.451396] x29: ffff800011ce3cc0 x28: 0000000000000000 > [ 6411.451398] x27: ffff000c04608040 x26: 0000000000000000 > [ 6411.451399] x25: ffff000c04608040 x24: 0000000000001000 > [ 6411.451401] x23: ffff0003f88c8530 x22: 0000000000001000 > [ 6411.451403] x21: ffff0003f88c8530 x20: 0000000000000000 > [ 6411.451404] x19: fffffe00201bcc80 x18: 0000000000000030 > [ 6411.451406] x17: 0000000000000000 x16: 0000000000000000 > [ 6411.451407] x15: ffff000c018f9760 x14: ffffffffffffffff > [ 6411.451409] x13: ffff8000119d72b0 x12: ffff8000119d6ee3 > [ 6411.451410] x11: ffff8000117b69b8 x10: 00000000ffff8000 > [ 6411.451412] x9 : ffff800010617534 x8 : 0000000000000000 > [ 6411.451413] x7 : ffff8000114f69b8 x6 : 000000000000000f > [ 6411.451415] x5 : 0000000000000000 x4 : 0000000000000000 > [ 6411.451416] x3 : 0000000000000400 x2 : 0000000000000000 > [ 6411.451418] x1 : 0000000000000000 x0 : 0000000000000000 > [ 6411.451420] Call trace: > [ 6411.451421] end_page_writeback+0x1c0/0x214 > [ 6411.451424] iomap_finish_page_writeback+0x13c/0x204 > [ 6411.451425] iomap_finish_ioend+0xe8/0x19c > [ 6411.451426] iomap_writepage_end_bio+0x38/0x50 > [ 6411.451427] bio_endio+0x168/0x1ec > [ 6411.451430] blk_update_request+0x278/0x3f0 > [ 6411.451432] blk_mq_end_request+0x34/0x15c > [ 6411.451435] virtblk_request_done+0x38/0x74 [virtio_blk] > [ 6411.451437] blk_done_softirq+0xc4/0x110 > [ 6411.451439] __do_softirq+0x128/0x38c > [ 6411.451441] __irq_exit_rcu+0x118/0x150 > [ 6411.451442] irq_exit+0x1c/0x30 > [ 6411.451445] __handle_domain_irq+0x8c/0xf0 > [ 6411.451446] gic_handle_irq+0x84/0x108 > [ 6411.451447] el1_irq+0xcc/0x180 > [ 6411.451448] arch_cpu_idle+0x18/0x40 > [ 6411.451450] default_idle_call+0x4c/0x1a0 > [ 6411.451453] cpuidle_idle_call+0x168/0x1e0 > [ 6411.451454] do_idle+0xb4/0x104 > [ 6411.451455] cpu_startup_entry+0x30/0x9c > [ 6411.451458] secondary_start_kernel+0x104/0x180 > [ 6411.451460] Code: d4210000 b0006161 910c8021 94013f4d (d4210000) > [ 6411.451462] ---[ end trace 4a88c6a074082f8c ]--- > [ 6411.451464] Kernel panic - not syncing: Oops - BUG: Fatal exception in interrupt > > 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/khugepaged.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 045cc57..529b117 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1798,7 +1798,8 @@ static void collapse_file(struct mm_struct *mm, > goto out_unlock; > } > > - if (!is_shmem && PageDirty(page)) { > + if (!is_shmem && (PageDirty(page) || > + PageWriteback(page))) { Why not check the writeback flag in the place before taking page lock too? > /* > * khugepaged only works on read-only fd, so this > * page is dirty because it hasn't been flushed > -- > 1.8.3.1 > >
> On Sep 8, 2021, at 12:56 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: >> >> Currently collapse_file does not explicitly check PG_writeback, instead, >> page_has_private and try_to_release_page are used to filter writeback >> pages. This does not work for xfs with blocksize equal to or larger > > I'm not quite sure if using try_to_release() to check the writeback > flag is on purpose or not, but it should be better to check the flag > more explicitly. Uh-huh. It is sure that try_to_release_page will check the writeback flag of page. But the place where check the writeback flag using: If (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL)) { ... } The original code will miss the page which in writeback status but has no private data. The XFS case that above mentioned belongs to. Thanks! > >> than pagesize, because in such case xfs has no page->private. >> >> This makes collapse_file bail out early for writeback page. Otherwise, >> xfs end_page_writeback will panic as follows. >> >> [ 6411.448211] page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:ffff0003f88c86a8 index:0x0 pfn:0x84ef32 >> [ 6411.448304] aops:xfs_address_space_operations [xfs] ino:30000b7 dentry name:"libtest.so" >> [ 6411.448312] flags: 0x57fffe0000008027(locked|referenced|uptodate|active|writeback) >> [ 6411.448317] raw: 57fffe0000008027 ffff80001b48bc28 ffff80001b48bc28 ffff0003f88c86a8 >> [ 6411.448321] raw: 0000000000000000 0000000000000000 00000000ffffffff ffff0000c3e9a000 >> [ 6411.448324] page dumped because: VM_BUG_ON_PAGE(((unsigned int) page_ref_count(page) + 127u <= 127u)) >> [ 6411.448327] page->mem_cgroup:ffff0000c3e9a000 >> [ 6411.448340] ------------[ cut here ]------------ >> [ 6411.448343] kernel BUG at include/linux/mm.h:1212! >> [ 6411.449288] Internal error: Oops - BUG: 0 [#1] SMP >> [ 6411.449786] Modules linked in: >> [ 6411.449790] BUG: Bad page state in process khugepaged pfn:84ef32 >> [ 6411.450143] xfs(E) >> [ 6411.450459] page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:0 index:0x0 pfn:0x84ef32 >> [ 6411.451361] 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) vfat(E) nfsd(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) >> [ 6411.451387] CPU: 25 PID: 0 Comm: swapper/25 Kdump: loaded Tainted: G W E >> [ 6411.451389] pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) >> [ 6411.451393] pc : end_page_writeback+0x1c0/0x214 >> [ 6411.451394] lr : end_page_writeback+0x1c0/0x214 >> [ 6411.451395] sp : ffff800011ce3cc0 >> [ 6411.451396] x29: ffff800011ce3cc0 x28: 0000000000000000 >> [ 6411.451398] x27: ffff000c04608040 x26: 0000000000000000 >> [ 6411.451399] x25: ffff000c04608040 x24: 0000000000001000 >> [ 6411.451401] x23: ffff0003f88c8530 x22: 0000000000001000 >> [ 6411.451403] x21: ffff0003f88c8530 x20: 0000000000000000 >> [ 6411.451404] x19: fffffe00201bcc80 x18: 0000000000000030 >> [ 6411.451406] x17: 0000000000000000 x16: 0000000000000000 >> [ 6411.451407] x15: ffff000c018f9760 x14: ffffffffffffffff >> [ 6411.451409] x13: ffff8000119d72b0 x12: ffff8000119d6ee3 >> [ 6411.451410] x11: ffff8000117b69b8 x10: 00000000ffff8000 >> [ 6411.451412] x9 : ffff800010617534 x8 : 0000000000000000 >> [ 6411.451413] x7 : ffff8000114f69b8 x6 : 000000000000000f >> [ 6411.451415] x5 : 0000000000000000 x4 : 0000000000000000 >> [ 6411.451416] x3 : 0000000000000400 x2 : 0000000000000000 >> [ 6411.451418] x1 : 0000000000000000 x0 : 0000000000000000 >> [ 6411.451420] Call trace: >> [ 6411.451421] end_page_writeback+0x1c0/0x214 >> [ 6411.451424] iomap_finish_page_writeback+0x13c/0x204 >> [ 6411.451425] iomap_finish_ioend+0xe8/0x19c >> [ 6411.451426] iomap_writepage_end_bio+0x38/0x50 >> [ 6411.451427] bio_endio+0x168/0x1ec >> [ 6411.451430] blk_update_request+0x278/0x3f0 >> [ 6411.451432] blk_mq_end_request+0x34/0x15c >> [ 6411.451435] virtblk_request_done+0x38/0x74 [virtio_blk] >> [ 6411.451437] blk_done_softirq+0xc4/0x110 >> [ 6411.451439] __do_softirq+0x128/0x38c >> [ 6411.451441] __irq_exit_rcu+0x118/0x150 >> [ 6411.451442] irq_exit+0x1c/0x30 >> [ 6411.451445] __handle_domain_irq+0x8c/0xf0 >> [ 6411.451446] gic_handle_irq+0x84/0x108 >> [ 6411.451447] el1_irq+0xcc/0x180 >> [ 6411.451448] arch_cpu_idle+0x18/0x40 >> [ 6411.451450] default_idle_call+0x4c/0x1a0 >> [ 6411.451453] cpuidle_idle_call+0x168/0x1e0 >> [ 6411.451454] do_idle+0xb4/0x104 >> [ 6411.451455] cpu_startup_entry+0x30/0x9c >> [ 6411.451458] secondary_start_kernel+0x104/0x180 >> [ 6411.451460] Code: d4210000 b0006161 910c8021 94013f4d (d4210000) >> [ 6411.451462] ---[ end trace 4a88c6a074082f8c ]--- >> [ 6411.451464] Kernel panic - not syncing: Oops - BUG: Fatal exception in interrupt >> >> 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/khugepaged.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 045cc57..529b117 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -1798,7 +1798,8 @@ static void collapse_file(struct mm_struct *mm, >> goto out_unlock; >> } >> >> - if (!is_shmem && PageDirty(page)) { >> + if (!is_shmem && (PageDirty(page) || >> + PageWriteback(page))) { > > Why not check the writeback flag in the place before taking page lock too? Thanks! Your words remind me. I will double check the writeback flag before and after taking page lock. Likes: + } else if (PageWriteback(page)) { + xas_unlock_irq(&xas); + result = SCAN_FAIL; + goto xa_unlocked; } else if (trylock_page(page)) { get_page(page); xas_unlock_irq(&xas); @@ -1798,7 +1802,8 @@ static void collapse_file(struct mm_struct *mm, goto out_unlock; } - if (!is_shmem && PageDirty(page)) { + if (!is_shmem && (PageDirty(page) || + PageWriteback(page))) { Thanks! > >> /* >> * khugepaged only works on read-only fd, so this >> * page is dirty because it hasn't been flushed >> -- >> 1.8.3.1
On Tue, Sep 7, 2021 at 7:16 PM Rongwei Wang <rongwei.wang@linux.alibaba.com> wrote: > > > > On Sep 8, 2021, at 12:56 AM, Yang Shi <shy828301@gmail.com> wrote: > > On Mon, Sep 6, 2021 at 5:12 AM Rongwei Wang > <rongwei.wang@linux.alibaba.com> wrote: > > > Currently collapse_file does not explicitly check PG_writeback, instead, > page_has_private and try_to_release_page are used to filter writeback > pages. This does not work for xfs with blocksize equal to or larger > > > I'm not quite sure if using try_to_release() to check the writeback > flag is on purpose or not, but it should be better to check the flag > more explicitly. > > Uh-huh. It is sure that try_to_release_page will check the writeback flag > of page. But the place where check the writeback flag using: > > If (page_has_private(page) && > !try_to_release_page(page, GFP_KERNEL)) { > ... > } > > The original code will miss the page which in writeback status but has no private data. > The XFS case that above mentioned belongs to. > > Thanks! > > > than pagesize, because in such case xfs has no page->private. > > This makes collapse_file bail out early for writeback page. Otherwise, > xfs end_page_writeback will panic as follows. > > [ 6411.448211] page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:ffff0003f88c86a8 index:0x0 pfn:0x84ef32 > [ 6411.448304] aops:xfs_address_space_operations [xfs] ino:30000b7 dentry name:"libtest.so" > [ 6411.448312] flags: 0x57fffe0000008027(locked|referenced|uptodate|active|writeback) > [ 6411.448317] raw: 57fffe0000008027 ffff80001b48bc28 ffff80001b48bc28 ffff0003f88c86a8 > [ 6411.448321] raw: 0000000000000000 0000000000000000 00000000ffffffff ffff0000c3e9a000 > [ 6411.448324] page dumped because: VM_BUG_ON_PAGE(((unsigned int) page_ref_count(page) + 127u <= 127u)) > [ 6411.448327] page->mem_cgroup:ffff0000c3e9a000 > [ 6411.448340] ------------[ cut here ]------------ > [ 6411.448343] kernel BUG at include/linux/mm.h:1212! > [ 6411.449288] Internal error: Oops - BUG: 0 [#1] SMP > [ 6411.449786] Modules linked in: > [ 6411.449790] BUG: Bad page state in process khugepaged pfn:84ef32 > [ 6411.450143] xfs(E) > [ 6411.450459] page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:0 index:0x0 pfn:0x84ef32 > [ 6411.451361] 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) vfat(E) nfsd(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) > [ 6411.451387] CPU: 25 PID: 0 Comm: swapper/25 Kdump: loaded Tainted: G W E > [ 6411.451389] pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) > [ 6411.451393] pc : end_page_writeback+0x1c0/0x214 > [ 6411.451394] lr : end_page_writeback+0x1c0/0x214 > [ 6411.451395] sp : ffff800011ce3cc0 > [ 6411.451396] x29: ffff800011ce3cc0 x28: 0000000000000000 > [ 6411.451398] x27: ffff000c04608040 x26: 0000000000000000 > [ 6411.451399] x25: ffff000c04608040 x24: 0000000000001000 > [ 6411.451401] x23: ffff0003f88c8530 x22: 0000000000001000 > [ 6411.451403] x21: ffff0003f88c8530 x20: 0000000000000000 > [ 6411.451404] x19: fffffe00201bcc80 x18: 0000000000000030 > [ 6411.451406] x17: 0000000000000000 x16: 0000000000000000 > [ 6411.451407] x15: ffff000c018f9760 x14: ffffffffffffffff > [ 6411.451409] x13: ffff8000119d72b0 x12: ffff8000119d6ee3 > [ 6411.451410] x11: ffff8000117b69b8 x10: 00000000ffff8000 > [ 6411.451412] x9 : ffff800010617534 x8 : 0000000000000000 > [ 6411.451413] x7 : ffff8000114f69b8 x6 : 000000000000000f > [ 6411.451415] x5 : 0000000000000000 x4 : 0000000000000000 > [ 6411.451416] x3 : 0000000000000400 x2 : 0000000000000000 > [ 6411.451418] x1 : 0000000000000000 x0 : 0000000000000000 > [ 6411.451420] Call trace: > [ 6411.451421] end_page_writeback+0x1c0/0x214 > [ 6411.451424] iomap_finish_page_writeback+0x13c/0x204 > [ 6411.451425] iomap_finish_ioend+0xe8/0x19c > [ 6411.451426] iomap_writepage_end_bio+0x38/0x50 > [ 6411.451427] bio_endio+0x168/0x1ec > [ 6411.451430] blk_update_request+0x278/0x3f0 > [ 6411.451432] blk_mq_end_request+0x34/0x15c > [ 6411.451435] virtblk_request_done+0x38/0x74 [virtio_blk] > [ 6411.451437] blk_done_softirq+0xc4/0x110 > [ 6411.451439] __do_softirq+0x128/0x38c > [ 6411.451441] __irq_exit_rcu+0x118/0x150 > [ 6411.451442] irq_exit+0x1c/0x30 > [ 6411.451445] __handle_domain_irq+0x8c/0xf0 > [ 6411.451446] gic_handle_irq+0x84/0x108 > [ 6411.451447] el1_irq+0xcc/0x180 > [ 6411.451448] arch_cpu_idle+0x18/0x40 > [ 6411.451450] default_idle_call+0x4c/0x1a0 > [ 6411.451453] cpuidle_idle_call+0x168/0x1e0 > [ 6411.451454] do_idle+0xb4/0x104 > [ 6411.451455] cpu_startup_entry+0x30/0x9c > [ 6411.451458] secondary_start_kernel+0x104/0x180 > [ 6411.451460] Code: d4210000 b0006161 910c8021 94013f4d (d4210000) > [ 6411.451462] ---[ end trace 4a88c6a074082f8c ]--- > [ 6411.451464] Kernel panic - not syncing: Oops - BUG: Fatal exception in interrupt > > 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/khugepaged.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 045cc57..529b117 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1798,7 +1798,8 @@ static void collapse_file(struct mm_struct *mm, > goto out_unlock; > } > > - if (!is_shmem && PageDirty(page)) { > + if (!is_shmem && (PageDirty(page) || > + PageWriteback(page))) { > > > Why not check the writeback flag in the place before taking page lock too? > > Thanks! Your words remind me. I will double check the writeback flag before > and after taking page lock. Likes: > > + } else if (PageWriteback(page)) { > + xas_unlock_irq(&xas); > + result = SCAN_FAIL; > + goto xa_unlocked; > } else if (trylock_page(page)) { > get_page(page); > xas_unlock_irq(&xas); > @@ -1798,7 +1802,8 @@ static void collapse_file(struct mm_struct *mm, > goto out_unlock; > } > > - if (!is_shmem && PageDirty(page)) { > + if (!is_shmem && (PageDirty(page) || > + PageWriteback(page))) { Yeah, this is what I meant. Thanks. > > Thanks! > > > /* > * khugepaged only works on read-only fd, so this > * page is dirty because it hasn't been flushed > -- > 1.8.3.1 > >
> On Sep 9, 2021, at 5:51 AM, Yang Shi <shy828301@gmail.com> wrote: > > On Tue, Sep 7, 2021 at 7:16 PM Rongwei Wang > <rongwei.wang@linux.alibaba.com <mailto:rongwei.wang@linux.alibaba.com>> wrote: >> >> >> >> On Sep 8, 2021, at 12:56 AM, Yang Shi <shy828301@gmail.com> wrote: >> >> On Mon, Sep 6, 2021 at 5:12 AM Rongwei Wang >> <rongwei.wang@linux.alibaba.com> wrote: >> >> >> Currently collapse_file does not explicitly check PG_writeback, instead, >> page_has_private and try_to_release_page are used to filter writeback >> pages. This does not work for xfs with blocksize equal to or larger >> >> >> I'm not quite sure if using try_to_release() to check the writeback >> flag is on purpose or not, but it should be better to check the flag >> more explicitly. >> >> Uh-huh. It is sure that try_to_release_page will check the writeback flag >> of page. But the place where check the writeback flag using: >> >> If (page_has_private(page) && >> !try_to_release_page(page, GFP_KERNEL)) { >> ... >> } >> >> The original code will miss the page which in writeback status but has no private data. >> The XFS case that above mentioned belongs to. >> >> Thanks! >> >> >> than pagesize, because in such case xfs has no page->private. >> >> This makes collapse_file bail out early for writeback page. Otherwise, >> xfs end_page_writeback will panic as follows. >> >> [ 6411.448211] page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:ffff0003f88c86a8 index:0x0 pfn:0x84ef32 >> [ 6411.448304] aops:xfs_address_space_operations [xfs] ino:30000b7 dentry name:"libtest.so" >> [ 6411.448312] flags: 0x57fffe0000008027(locked|referenced|uptodate|active|writeback) >> [ 6411.448317] raw: 57fffe0000008027 ffff80001b48bc28 ffff80001b48bc28 ffff0003f88c86a8 >> [ 6411.448321] raw: 0000000000000000 0000000000000000 00000000ffffffff ffff0000c3e9a000 >> [ 6411.448324] page dumped because: VM_BUG_ON_PAGE(((unsigned int) page_ref_count(page) + 127u <= 127u)) >> [ 6411.448327] page->mem_cgroup:ffff0000c3e9a000 >> [ 6411.448340] ------------[ cut here ]------------ >> [ 6411.448343] kernel BUG at include/linux/mm.h:1212! >> [ 6411.449288] Internal error: Oops - BUG: 0 [#1] SMP >> [ 6411.449786] Modules linked in: >> [ 6411.449790] BUG: Bad page state in process khugepaged pfn:84ef32 >> [ 6411.450143] xfs(E) >> [ 6411.450459] page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:0 index:0x0 pfn:0x84ef32 >> [ 6411.451361] 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) vfat(E) nfsd(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) >> [ 6411.451387] CPU: 25 PID: 0 Comm: swapper/25 Kdump: loaded Tainted: G W E >> [ 6411.451389] pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) >> [ 6411.451393] pc : end_page_writeback+0x1c0/0x214 >> [ 6411.451394] lr : end_page_writeback+0x1c0/0x214 >> [ 6411.451395] sp : ffff800011ce3cc0 >> [ 6411.451396] x29: ffff800011ce3cc0 x28: 0000000000000000 >> [ 6411.451398] x27: ffff000c04608040 x26: 0000000000000000 >> [ 6411.451399] x25: ffff000c04608040 x24: 0000000000001000 >> [ 6411.451401] x23: ffff0003f88c8530 x22: 0000000000001000 >> [ 6411.451403] x21: ffff0003f88c8530 x20: 0000000000000000 >> [ 6411.451404] x19: fffffe00201bcc80 x18: 0000000000000030 >> [ 6411.451406] x17: 0000000000000000 x16: 0000000000000000 >> [ 6411.451407] x15: ffff000c018f9760 x14: ffffffffffffffff >> [ 6411.451409] x13: ffff8000119d72b0 x12: ffff8000119d6ee3 >> [ 6411.451410] x11: ffff8000117b69b8 x10: 00000000ffff8000 >> [ 6411.451412] x9 : ffff800010617534 x8 : 0000000000000000 >> [ 6411.451413] x7 : ffff8000114f69b8 x6 : 000000000000000f >> [ 6411.451415] x5 : 0000000000000000 x4 : 0000000000000000 >> [ 6411.451416] x3 : 0000000000000400 x2 : 0000000000000000 >> [ 6411.451418] x1 : 0000000000000000 x0 : 0000000000000000 >> [ 6411.451420] Call trace: >> [ 6411.451421] end_page_writeback+0x1c0/0x214 >> [ 6411.451424] iomap_finish_page_writeback+0x13c/0x204 >> [ 6411.451425] iomap_finish_ioend+0xe8/0x19c >> [ 6411.451426] iomap_writepage_end_bio+0x38/0x50 >> [ 6411.451427] bio_endio+0x168/0x1ec >> [ 6411.451430] blk_update_request+0x278/0x3f0 >> [ 6411.451432] blk_mq_end_request+0x34/0x15c >> [ 6411.451435] virtblk_request_done+0x38/0x74 [virtio_blk] >> [ 6411.451437] blk_done_softirq+0xc4/0x110 >> [ 6411.451439] __do_softirq+0x128/0x38c >> [ 6411.451441] __irq_exit_rcu+0x118/0x150 >> [ 6411.451442] irq_exit+0x1c/0x30 >> [ 6411.451445] __handle_domain_irq+0x8c/0xf0 >> [ 6411.451446] gic_handle_irq+0x84/0x108 >> [ 6411.451447] el1_irq+0xcc/0x180 >> [ 6411.451448] arch_cpu_idle+0x18/0x40 >> [ 6411.451450] default_idle_call+0x4c/0x1a0 >> [ 6411.451453] cpuidle_idle_call+0x168/0x1e0 >> [ 6411.451454] do_idle+0xb4/0x104 >> [ 6411.451455] cpu_startup_entry+0x30/0x9c >> [ 6411.451458] secondary_start_kernel+0x104/0x180 >> [ 6411.451460] Code: d4210000 b0006161 910c8021 94013f4d (d4210000) >> [ 6411.451462] ---[ end trace 4a88c6a074082f8c ]--- >> [ 6411.451464] Kernel panic - not syncing: Oops - BUG: Fatal exception in interrupt >> >> 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/khugepaged.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 045cc57..529b117 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -1798,7 +1798,8 @@ static void collapse_file(struct mm_struct *mm, >> goto out_unlock; >> } >> >> - if (!is_shmem && PageDirty(page)) { >> + if (!is_shmem && (PageDirty(page) || >> + PageWriteback(page))) { >> >> >> Why not check the writeback flag in the place before taking page lock too? >> >> Thanks! Your words remind me. I will double check the writeback flag before >> and after taking page lock. Likes: >> >> + } else if (PageWriteback(page)) { >> + xas_unlock_irq(&xas); >> + result = SCAN_FAIL; >> + goto xa_unlocked; >> } else if (trylock_page(page)) { >> get_page(page); >> xas_unlock_irq(&xas); >> @@ -1798,7 +1802,8 @@ static void collapse_file(struct mm_struct *mm, >> goto out_unlock; >> } >> >> - if (!is_shmem && PageDirty(page)) { >> + if (!is_shmem && (PageDirty(page) || >> + PageWriteback(page))) { > > Yeah, this is what I meant. Thanks. OK, I will update these two patches and send PATCH v2 after receiving comments from Matthew. Thanks! > >> >> Thanks! >> >> >> /* >> * khugepaged only works on read-only fd, so this >> * page is dirty because it hasn't been flushed >> -- >> 1.8.3.1
diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 045cc57..529b117 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1798,7 +1798,8 @@ static void collapse_file(struct mm_struct *mm, goto out_unlock; } - if (!is_shmem && PageDirty(page)) { + if (!is_shmem && (PageDirty(page) || + PageWriteback(page))) { /* * khugepaged only works on read-only fd, so this * page is dirty because it hasn't been flushed
Currently collapse_file does not explicitly check PG_writeback, instead, page_has_private and try_to_release_page are used to filter writeback pages. This does not work for xfs with blocksize equal to or larger than pagesize, because in such case xfs has no page->private. This makes collapse_file bail out early for writeback page. Otherwise, xfs end_page_writeback will panic as follows. [ 6411.448211] page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:ffff0003f88c86a8 index:0x0 pfn:0x84ef32 [ 6411.448304] aops:xfs_address_space_operations [xfs] ino:30000b7 dentry name:"libtest.so" [ 6411.448312] flags: 0x57fffe0000008027(locked|referenced|uptodate|active|writeback) [ 6411.448317] raw: 57fffe0000008027 ffff80001b48bc28 ffff80001b48bc28 ffff0003f88c86a8 [ 6411.448321] raw: 0000000000000000 0000000000000000 00000000ffffffff ffff0000c3e9a000 [ 6411.448324] page dumped because: VM_BUG_ON_PAGE(((unsigned int) page_ref_count(page) + 127u <= 127u)) [ 6411.448327] page->mem_cgroup:ffff0000c3e9a000 [ 6411.448340] ------------[ cut here ]------------ [ 6411.448343] kernel BUG at include/linux/mm.h:1212! [ 6411.449288] Internal error: Oops - BUG: 0 [#1] SMP [ 6411.449786] Modules linked in: [ 6411.449790] BUG: Bad page state in process khugepaged pfn:84ef32 [ 6411.450143] xfs(E) [ 6411.450459] page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:0 index:0x0 pfn:0x84ef32 [ 6411.451361] 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) vfat(E) nfsd(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) [ 6411.451387] CPU: 25 PID: 0 Comm: swapper/25 Kdump: loaded Tainted: G W E [ 6411.451389] pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) [ 6411.451393] pc : end_page_writeback+0x1c0/0x214 [ 6411.451394] lr : end_page_writeback+0x1c0/0x214 [ 6411.451395] sp : ffff800011ce3cc0 [ 6411.451396] x29: ffff800011ce3cc0 x28: 0000000000000000 [ 6411.451398] x27: ffff000c04608040 x26: 0000000000000000 [ 6411.451399] x25: ffff000c04608040 x24: 0000000000001000 [ 6411.451401] x23: ffff0003f88c8530 x22: 0000000000001000 [ 6411.451403] x21: ffff0003f88c8530 x20: 0000000000000000 [ 6411.451404] x19: fffffe00201bcc80 x18: 0000000000000030 [ 6411.451406] x17: 0000000000000000 x16: 0000000000000000 [ 6411.451407] x15: ffff000c018f9760 x14: ffffffffffffffff [ 6411.451409] x13: ffff8000119d72b0 x12: ffff8000119d6ee3 [ 6411.451410] x11: ffff8000117b69b8 x10: 00000000ffff8000 [ 6411.451412] x9 : ffff800010617534 x8 : 0000000000000000 [ 6411.451413] x7 : ffff8000114f69b8 x6 : 000000000000000f [ 6411.451415] x5 : 0000000000000000 x4 : 0000000000000000 [ 6411.451416] x3 : 0000000000000400 x2 : 0000000000000000 [ 6411.451418] x1 : 0000000000000000 x0 : 0000000000000000 [ 6411.451420] Call trace: [ 6411.451421] end_page_writeback+0x1c0/0x214 [ 6411.451424] iomap_finish_page_writeback+0x13c/0x204 [ 6411.451425] iomap_finish_ioend+0xe8/0x19c [ 6411.451426] iomap_writepage_end_bio+0x38/0x50 [ 6411.451427] bio_endio+0x168/0x1ec [ 6411.451430] blk_update_request+0x278/0x3f0 [ 6411.451432] blk_mq_end_request+0x34/0x15c [ 6411.451435] virtblk_request_done+0x38/0x74 [virtio_blk] [ 6411.451437] blk_done_softirq+0xc4/0x110 [ 6411.451439] __do_softirq+0x128/0x38c [ 6411.451441] __irq_exit_rcu+0x118/0x150 [ 6411.451442] irq_exit+0x1c/0x30 [ 6411.451445] __handle_domain_irq+0x8c/0xf0 [ 6411.451446] gic_handle_irq+0x84/0x108 [ 6411.451447] el1_irq+0xcc/0x180 [ 6411.451448] arch_cpu_idle+0x18/0x40 [ 6411.451450] default_idle_call+0x4c/0x1a0 [ 6411.451453] cpuidle_idle_call+0x168/0x1e0 [ 6411.451454] do_idle+0xb4/0x104 [ 6411.451455] cpu_startup_entry+0x30/0x9c [ 6411.451458] secondary_start_kernel+0x104/0x180 [ 6411.451460] Code: d4210000 b0006161 910c8021 94013f4d (d4210000) [ 6411.451462] ---[ end trace 4a88c6a074082f8c ]--- [ 6411.451464] Kernel panic - not syncing: Oops - BUG: Fatal exception in interrupt 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/khugepaged.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)