Date:   Wed, 22 Jun 2022 19:59:27 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Wang Yugui <wangyugui@...-tech.com>
CC:     Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "david@...morbit.com" <david@...morbit.com>,
        "tgraf@...g.ch" <tgraf@...g.ch>, Jeff Layton <jlayton@...hat.com>
Subject: Re: [PATCH RFC 00/30] Overhaul NFSD filecache



> On Jun 22, 2022, at 3:04 PM, Chuck Lever III <chuck.lever@...cle.com> wrote:
> 
> 
> 
>> On Jun 22, 2022, at 2:36 PM, Wang Yugui <wangyugui@...-tech.com> wrote:
>> 
>> Hi,
>> 
>> fstests generic/531 triggered a panic on kernel 5.19.0-rc3 with this
>> patchset.
> 
> As I mention in the cover letter, I haven't tried running generic/531
> yet -- no claim at all that this is finished work and that #386 has
> been fixed at this point. I'm merely interested in comments on the
> general approach.
> 
> 
>> [ 405.478056] BUG: kernel NULL pointer dereference, address: 0000000000000049
> 
> The "RIP: " tells the location of the crash. Notice that the call
> trace here does not include that information. From your attachment:
> 
> [ 405.518022] RIP: 0010:nfsd_do_file_acquire+0x4e1/0xb80 [nfsd]
> 
> To match that to a line of source code:
> 
> [cel@...et ~]$ cd src/linux/linux/
> [cel@...et linux]$ scripts/faddr2line ../obj/manet/fs/nfsd/filecache.o nfsd_do_file_acquire+0x4e1
> nfsd_do_file_acquire+0x4e1/0xfc0:
> rht_bucket_insert at /home/cel/src/linux/linux/include/linux/rhashtable.h:303
> (inlined by) __rhashtable_insert_fast at /home/cel/src/linux/linux/include/linux/rhashtable.h:718
> (inlined by) rhashtable_lookup_get_insert_key at /home/cel/src/linux/linux/include/linux/rhashtable.h:982
> (inlined by) nfsd_file_insert at /home/cel/src/linux/linux/fs/nfsd/filecache.c:1031
> (inlined by) nfsd_do_file_acquire at /home/cel/src/linux/linux/fs/nfsd/filecache.c:1089
> [cel@...et linux]$
> 
> This is an example, I'm sure my compiled objects don't match yours.
> 
> And, now that I've added observability, you should be able to do:
> 
> # watch cat /proc/fs/nfsd/filecache
> 
> to see how many items are in the hash and LRU list while the test
> is running.
> 
> 
>> [ 405.608016] Call Trace:
>> [ 405.608016] <TASK>
>> [ 405.613020] nfs4_get_vfs_file+0x325/0x410 [nfsd]
>> [ 405.618018] nfsd4_process_open2+0x4ba/0x16d0 [nfsd]
>> [ 405.623016] ? inode_get_bytes+0x38/0x40
>> [ 405.623016] ? nfsd_permission+0x97/0xf0 [nfsd]
>> [ 405.628022] ? fh_verify+0x1cc/0x6f0 [nfsd]
>> [ 405.633025] nfsd4_open+0x640/0xb30 [nfsd]
>> [ 405.638025] nfsd4_proc_compound+0x3bd/0x710 [nfsd]
>> [ 405.643017] nfsd_dispatch+0x143/0x270 [nfsd]
>> [ 405.648019] svc_process_common+0x3bf/0x5b0 [sunrpc]

I was able to trigger something that looks very much like this crash.
If you remove this line from fs/nfsd/filecache.c:

	.max_size		= 131072, /* buckets */

things get a lot more stable for generic/531.

I'm looking into the issue now.


>> more detail in attachment file(531.dmesg)
>> 
>> local.config of fstests:
>> 	export NFS_MOUNT_OPTIONS="-o rw,relatime,vers=4.2,nconnect=8"
>> changes of generic/531
>> 	max_allowable_files=$(( 1 * 1024 * 1024 / $nr_cpus / 2 ))
> 
> Changed from:
> 
> 	max_allowable_files=$(( $(cat /proc/sys/fs/file-max) / $nr_cpus / 2 ))
> 
> For my own information, what's $nr_cpus in your test?
> 
> Aside from the max_allowable_files setting, can you tell how the
> test determines when it should stop creating files? Is it looking
> for a particular error code from open(2), for instance?
> 
> On my client:
> 
> [cel@...isot generic]$ cat /proc/sys/fs/file-max
> 9223372036854775807
> [cel@...isot generic]$
> 
> I wonder if it's realistic to expect an NFSv4 server to support
> that many open files. Is 9 quintillion files really something
> I'm going to have to engineer for, or is this just a crazy
> test?
> 
> 
>> Best Regards
>> Wang Yugui (wangyugui@...-tech.com)
>> 2022/06/23
>> 
>>> This series overhauls the NFSD filecache, a cache of server-side
>>> "struct file" objects recently used by NFS clients. The purposes of
>>> this overhaul are an immediate improvement in cache scalability in
>>> the number of open files, and preparation for further improvements.
>>> 
>>> There are three categories of patches in this series:
>>> 
>>> 1. Add observability of cache operation so we can see what we're
>>> doing as changes are made to the code.
>>> 
>>> 2. Improve the scalability of filecache garbage collection,
>>> addressing several bugs along the way.
>>> 
>>> 3. Improve the scalability of the filecache hash table by converting
>>> it to use rhashtable.
>>> 
>>> The series as it stands survives typical test workloads. Running
>>> stress-tests like generic/531 is the next step.
>>> 
>>> These patches are also available in the linux-nfs-bugzilla-386
>>> branch of
>>> 
>>> https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git 
>>> 
>>> ---
>>> 
>>> Chuck Lever (30):
>>> NFSD: Report filecache LRU size
>>> NFSD: Report count of calls to nfsd_file_acquire()
>>> NFSD: Report count of freed filecache items
>>> NFSD: Report average age of filecache items
>>> NFSD: Add nfsd_file_lru_dispose_list() helper
>>> NFSD: Refactor nfsd_file_gc()
>>> NFSD: Refactor nfsd_file_lru_scan()
>>> NFSD: Report the number of items evicted by the LRU walk
>>> NFSD: Record number of flush calls
>>> NFSD: Report filecache item construction failures
>>> NFSD: Zero counters when the filecache is re-initialized
>>> NFSD: Hook up the filecache stat file
>>> NFSD: WARN when freeing an item still linked via nf_lru
>>> NFSD: Trace filecache LRU activity
>>> NFSD: Leave open files out of the filecache LRU
>>> NFSD: Fix the filecache LRU shrinker
>>> NFSD: Never call nfsd_file_gc() in foreground paths
>>> NFSD: No longer record nf_hashval in the trace log
>>> NFSD: Remove lockdep assertion from unhash_and_release_locked()
>>> NFSD: nfsd_file_unhash can compute hashval from nf->nf_inode
>>> NFSD: Refactor __nfsd_file_close_inode()
>>> NFSD: nfsd_file_hash_remove can compute hashval
>>> NFSD: Remove nfsd_file::nf_hashval
>>> NFSD: Remove stale comment from nfsd_file_acquire()
>>> NFSD: Clean up "open file" case in nfsd_file_acquire()
>>> NFSD: Document nfsd_file_cache_purge() API contract
>>> NFSD: Replace the "init once" mechanism
>>> NFSD: Set up an rhashtable for the filecache
>>> NFSD: Convert the filecache to use rhashtable
>>> NFSD: Clean up unusued code after rhashtable conversion
>>> 
>>> 
>>> fs/nfsd/filecache.c | 677 +++++++++++++++++++++++++++-----------------
>>> fs/nfsd/filecache.h | 6 +-
>>> fs/nfsd/nfsctl.c | 10 +
>>> fs/nfsd/trace.h | 117 ++++++--
>>> 4 files changed, 522 insertions(+), 288 deletions(-)
>>> 
>>> --
>>> Chuck Lever
>> 
>> <531.dmesg>
> 
> --
> Chuck Lever

--
Chuck Lever

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