Re: [PATCH] Revert "btrfs: compression: don't try to compress if we don't have enough pages"

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

I'm sorry that this panic is not caused by this patch.

btrfs/244 seems a new test case to  check some bug-fix that yet not been
merged in to 5.14.

# btrfs/244
# The kernel fix is titled "btrfs: fix NULL pointer dereference when
# deleting device by invalid id".

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2021/08/27

> Hi,
> 
> With this patch, kernel panic when xfstest btrfs/244
> 
> #btrfs version: 5.13.x (with some patches from 5.14), although shown as 5.10.61.
> 
> [  131.802619] BUG: kernel NULL pointer dereference, address:
> 0000000000000000
> [  131.810837] #PF: supervisor read access in kernel mode
> [  131.817026] #PF: error_code(0x0000) - not-present page
> [  131.823240] PGD 0 P4D 0
> [  131.826521] Oops: 0000 [#1] SMP NOPTI
> [  131.831029] CPU: 37 PID: 4434 Comm: btrfs Not tainted 5.10.61-1.el7.x86_64 #1
> [  131.839478] Hardware name: Dell Inc. PowerEdge T620/02CD1V, BIOS 2.9.0 12/06/2019
> [  131.848315] RIP: 0010:btrfs_rm_device+0x248/0x4f0 [btrfs]
> [  131.854805] Code: 8b 45 30 48 89 df 48 83 40 48 01 e8 92 cb 14 ea e9 e2 fe ff ff b9 08 00 00 00 48 c7 c7 f7
>  9a a4 c0 4c 89 e6 41 bf 06 00 00 00 <f3> a6 0f 97 c0 1c 00 84 c0 0f 84 be fe ff ff e9 b6 fe ff ff 48 89
> [  131.876730] RSP: 0018:ffff9ff54e01fd80 EFLAGS: 00010246
> [  131.883000] RAX: fffffffffffffffe RBX: ffff8c0b0a8cd000 RCX: 0000000000000008
> [  131.891463] RDX: fffffffffffffffe RSI: 0000000000000000 RDI: ffffffffc0a49af7
> [  131.899854] RBP: fffffffffffffffe R08: ffff8c0d4872f400 R09: 0000000000001000
> [  131.908262] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> [  131.916686] R13: 0000000000000003 R14: ffff8c0d4872f400 R15: 0000000000000006
> [  131.925070] FS:  00007ffa0f6029c0(0000) GS:ffff8c1abfc80000(0000) knlGS:0000000000000000
> [  131.934608] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  131.941449] CR2: 0000000000000000 CR3: 0000002179c4e001 CR4: 00000000001706e0
> [  131.949883] Call Trace:
> [  131.953090]  ? __check_object_size+0x162/0x180
> [  131.958593]  btrfs_ioctl+0x1870/0x2fd0 [btrfs]
> [  131.963997]  ? do_fault+0x22e/0x490
> [  131.968370]  ? __handle_mm_fault+0x5e8/0x7c0
> [  131.973582]  ? __x64_sys_ioctl+0x84/0xc0
> [  131.978370]  __x64_sys_ioctl+0x84/0xc0
> [  131.982999]  do_syscall_64+0x33/0x40
> [  131.987445]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [  131.993511] RIP: 0033:0x7ffa0e16762b
> [  131.997925] Code: 0f 1e fa 48 8b 05 5d b8 2c 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 0f 1f 44 00
>  00 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 2d b8 2c 00 f7 d8 64 89 01 48
> [  132.019844] RSP: 002b:00007ffe18adeeb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> [  132.028777] RAX: ffffffffffffffda RBX: 00007ffe18ae1070 RCX: 00007ffa0e16762b
> [  132.037222] RDX: 00007ffe18adfee0 RSI: 000000005000943a RDI: 0000000000000003
> [  132.045715] RBP: 00007ffe18adfee0 R08: 00007ffe18ae3221 R09: 0000000000000000
> [  132.054134] R10: 00007ffa0e1e51e0 R11: 0000000000000246 R12: 0000000000000001
> [  132.062617] R13: 0000000000000000 R14: 0000000000000003 R15: 00007ffe18ae1078
> [  132.071037] Modules linked in: dm_flakey rpcsec_gss_krb5 nfsv4 dns_resolver nfs fscache rfkill iTCO_wdt int
> el_pmc_bxt intel_rapl_msr iTCO_vendor_support dcdbas intel_rapl_common sb_edac x86_pkg_temp_thermal intel_powe
> rclamp coretemp ipmi_ssif kvm_intel kvm irqbypass rapl intel_cstate ipmi_si mei_me ipmi_devintf intel_uncore j
> oydev ipmi_msghandler mei lpc_ich acpi_power_meter nvme_rdma nvme_fabrics rdma_cm iw_cm ib_cm rdmavt nfsd rdma
> _rxe ib_uverbs ip6_udp_tunnel udp_tunnel ib_core auth_rpcgss nfs_acl lockd grace nfs_ssc ip_tables xfs mgag200
>  drm_kms_helper btrfs cec crct10dif_pclmul crc32_pclmul crc32c_intel xor raid6_pq drm bnx2x nvme mpt3sas ghash
> _clmulni_intel igb pcspkr mdio megaraid_sas nvme_core raid_class dca i2c_algo_bit scsi_transport_sas wmi dm_mu
> ltipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua sunrpc i2c_dev
> [  132.155588] CR2: 0000000000000000
> [  132.159878] ---[ end trace 5ad61f759e33fdff ]---
> [  132.169659] RIP: 0010:btrfs_rm_device+0x248/0x4f0 [btrfs]
> [  132.176237] Code: 8b 45 30 48 89 df 48 83 40 48 01 e8 92 cb 14 ea e9 e2 fe ff ff b9 08 00 00 00 48 c7 c7 f7
>  9a a4 c0 4c 89 e6 41 bf 06 00 00 00 <f3> a6 0f 97 c0 1c 00 84 c0 0f 84 be fe ff ff e9 b6 fe ff ff 48 89
> [  132.198409] RSP: 0018:ffff9ff54e01fd80 EFLAGS: 00010246
> [  132.204856] RAX: fffffffffffffffe RBX: ffff8c0b0a8cd000 RCX: 0000000000000008
> [  132.213467] RDX: fffffffffffffffe RSI: 0000000000000000 RDI: ffffffffc0a49af7
> [  132.222039] RBP: fffffffffffffffe R08: ffff8c0d4872f400 R09: 0000000000001000
> [  132.230657] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> [  132.239222] R13: 0000000000000003 R14: ffff8c0d4872f400 R15: 0000000000000006
> [  132.247813] FS:  00007ffa0f6029c0(0000) GS:ffff8c1abfc80000(0000) knlGS:0000000000000000
> [  132.257461] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  132.264459] CR2: 0000000000000000 CR3: 0000002179c4e001 CR4: 00000000001706e0
> [  132.273009] Kernel panic - not syncing: Fatal exception
> [  132.447157] Kernel Offset: 0x29000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xfffff
> fffbfffffff)
> [  132.462761] ---[ end Kernel panic - not syncing: Fatal exception ]---
> 
> Best Regards
> Wang Yugui (wangyugui@e16-tech.com)
> 2021/08/27
> 
> > This reverts commit f2165627319ffd33a6217275e5690b1ab5c45763.
> > 
> > [BUG]
> > It's no longer possible to create compressed inline extent after commit
> > f2165627319f ("btrfs: compression: don't try to compress if we don't
> > have enough pages").
> > 
> > [CAUSE]
> > For compression code, there are several possible reasons we have a range
> > that needs to be compressed while it's no more than one page.
> > 
> > - Compressed inline write
> >   The data is always smaller than one sector.
> > 
> > - Compressed subpage write
> >   For the incoming subpage compressed write support, we require page
> >   alignment of the delalloc range.
> >   And for 64K page size, we can compress just one page into smaller
> >   sectors.
> > 
> > For those reasons, the requirement for the data to be more than one page
> > is not correct, and is already causing regression for compressed inline
> > data writeback.
> > 
> > [FIX]
> > Fix it by reverting the offending commit.
> > 
> > Fixes: f2165627319f ("btrfs: compression: don't try to compress if we don't have enough pages")
> > Signed-off-by: Qu Wenruo <wqu@suse.com>
> > ---
> >  fs/btrfs/inode.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > index 2aa9646bce56..2b7fe98adec2 100644
> > --- a/fs/btrfs/inode.c
> > +++ b/fs/btrfs/inode.c
> > @@ -632,7 +632,7 @@ static noinline int compress_file_range(struct async_chunk *async_chunk)
> >  	 * inode has not been flagged as nocompress.  This flag can
> >  	 * change at any time if we discover bad compression ratios.
> >  	 */
> > -	if (nr_pages > 1 && inode_need_compress(BTRFS_I(inode), start, end)) {
> > +	if (inode_need_compress(BTRFS_I(inode), start, end)) {
> >  		WARN_ON(pages);
> >  		pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
> >  		if (!pages) {
> > -- 
> > 2.32.0
>