From: "Darrick J. Wong" darrick.wong@oracle.com
[ Upstream commit 27fb5a72f50aa770dd38b0478c07acacef97e3e7 ]
I noticed that fsfreeze can take a very long time to freeze an XFS if there happens to be a GETFSMAP caller running in the background. I also happened to notice the following in dmesg:
------------[ cut here ]------------ WARNING: CPU: 2 PID: 43492 at fs/xfs/xfs_super.c:853 xfs_quiesce_attr+0x83/0x90 [xfs] Modules linked in: xfs libcrc32c ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 ip_set_hash_ip ip_set_hash_net xt_tcpudp xt_set ip_set_hash_mac ip_set nfnetlink ip6table_filter ip6_tables bfq iptable_filter sch_fq_codel ip_tables x_tables nfsv4 af_packet [last unloaded: xfs] CPU: 2 PID: 43492 Comm: xfs_io Not tainted 5.6.0-rc4-djw #rc4 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1ubuntu1 04/01/2014 RIP: 0010:xfs_quiesce_attr+0x83/0x90 [xfs] Code: 7c 07 00 00 85 c0 75 22 48 89 df 5b e9 96 c1 00 00 48 c7 c6 b0 2d 38 a0 48 89 df e8 57 64 ff ff 8b 83 7c 07 00 00 85 c0 74 de <0f> 0b 48 89 df 5b e9 72 c1 00 00 66 90 0f 1f 44 00 00 41 55 41 54 RSP: 0018:ffffc900030f3e28 EFLAGS: 00010202 RAX: 0000000000000001 RBX: ffff88802ac54000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffffffff81e4a6f0 RDI: 00000000ffffffff RBP: ffff88807859f070 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000010 R12: 0000000000000000 R13: ffff88807859f388 R14: ffff88807859f4b8 R15: ffff88807859f5e8 FS: 00007fad1c6c0fc0(0000) GS:ffff88807e000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f0c7d237000 CR3: 0000000077f01003 CR4: 00000000001606a0 Call Trace: xfs_fs_freeze+0x25/0x40 [xfs] freeze_super+0xc8/0x180 do_vfs_ioctl+0x70b/0x750 ? __fget_files+0x135/0x210 ksys_ioctl+0x3a/0xb0 __x64_sys_ioctl+0x16/0x20 do_syscall_64+0x50/0x1a0 entry_SYSCALL_64_after_hwframe+0x49/0xbe
These two things appear to be related. The assertion trips when another thread initiates a fsmap request (which uses an empty transaction) after the freezer waited for m_active_trans to hit zero but before the the freezer executes the WARN_ON just prior to calling xfs_log_quiesce.
The lengthy delays in freezing happen because the freezer calls xfs_wait_buftarg to clean out the buffer lru list. Meanwhile, the GETFSMAP caller is continuing to grab and release buffers, which means that it can take a very long time for the buffer lru list to empty out.
We fix both of these races by calling sb_start_write to obtain freeze protection while using empty transactions for GETFSMAP and for metadata scrubbing. The other two users occur during mount, during which time we cannot fs freeze.
Signed-off-by: Darrick J. Wong darrick.wong@oracle.com Reviewed-by: Dave Chinner dchinner@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/xfs/scrub/scrub.c | 9 +++++++++ fs/xfs/xfs_fsmap.c | 9 +++++++++ fs/xfs/xfs_trans.c | 5 +++++ 3 files changed, 23 insertions(+)
diff --git a/fs/xfs/scrub/scrub.c b/fs/xfs/scrub/scrub.c index f1775bb193135..8ebf35b115ce2 100644 --- a/fs/xfs/scrub/scrub.c +++ b/fs/xfs/scrub/scrub.c @@ -168,6 +168,7 @@ xchk_teardown( xfs_irele(sc->ip); sc->ip = NULL; } + sb_end_write(sc->mp->m_super); if (sc->flags & XCHK_REAPING_DISABLED) xchk_start_reaping(sc); if (sc->flags & XCHK_HAS_QUOTAOFFLOCK) { @@ -490,6 +491,14 @@ xfs_scrub_metadata( sc.ops = &meta_scrub_ops[sm->sm_type]; sc.sick_mask = xchk_health_mask_for_scrub_type(sm->sm_type); retry_op: + /* + * If freeze runs concurrently with a scrub, the freeze can be delayed + * indefinitely as we walk the filesystem and iterate over metadata + * buffers. Freeze quiesces the log (which waits for the buffer LRU to + * be emptied) and that won't happen while checking is running. + */ + sb_start_write(mp->m_super); + /* Set up for the operation. */ error = sc.ops->setup(&sc, ip); if (error) diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c index 918456ca29e16..442fd4311f180 100644 --- a/fs/xfs/xfs_fsmap.c +++ b/fs/xfs/xfs_fsmap.c @@ -896,6 +896,14 @@ xfs_getfsmap( info.format_arg = arg; info.head = head;
+ /* + * If fsmap runs concurrently with a scrub, the freeze can be delayed + * indefinitely as we walk the rmapbt and iterate over metadata + * buffers. Freeze quiesces the log (which waits for the buffer LRU to + * be emptied) and that won't happen while we're reading buffers. + */ + sb_start_write(mp->m_super); + /* For each device we support... */ for (i = 0; i < XFS_GETFSMAP_DEVS; i++) { /* Is this device within the range the user asked for? */ @@ -935,6 +943,7 @@ xfs_getfsmap(
if (tp) xfs_trans_cancel(tp); + sb_end_write(mp->m_super); head->fmh_oflags = FMH_OF_DEV_T; return error; } diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c index 3b208f9a865cb..a65dc227e40d0 100644 --- a/fs/xfs/xfs_trans.c +++ b/fs/xfs/xfs_trans.c @@ -306,6 +306,11 @@ xfs_trans_alloc( * * Note the zero-length reservation; this transaction MUST be cancelled * without any dirty data. + * + * Callers should obtain freeze protection to avoid two conflicts with fs + * freezing: (1) having active transactions trip the m_active_trans ASSERTs; + * and (2) grabbing buffers at the same time that freeze is trying to drain + * the buffer LRU list. */ int xfs_trans_alloc_empty(