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Date: Fri, 3 Jun 2022 20:10:53 +0800
From: Xiubo Li <xiubli@...hat.com>
To: Luís Henriques <lhenriques@...e.de>
Cc: Jeff Layton <jlayton@...nel.org>,
Ilya Dryomov <idryomov@...il.com>,
Gregory Farnum <gfarnum@...hat.com>,
ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v4] ceph: prevent a client from exceeding the MDS
maximum xattr size
On 6/3/22 7:52 PM, Luís Henriques wrote:
> Xiubo Li <xiubli@...hat.com> writes:
>
>> On 6/2/22 10:36 PM, Luís Henriques wrote:
>>> The MDS tries to enforce a limit on the total key/values in extended
>>> attributes. However, this limit is enforced only if doing a synchronous
>>> operation (MDS_OP_SETXATTR) -- if we're buffering the xattrs, the MDS
>>> doesn't have a chance to enforce these limits.
>>>
>>> This patch adds support for decoding the xattrs maximum size setting that is
>>> distributed in the mdsmap. Then, when setting an xattr, the kernel client
>>> will revert to do a synchronous operation if that maximum size is exceeded.
>>>
>>> While there, fix a dout() that would trigger a printk warning:
>>>
>>> [ 98.718078] ------------[ cut here ]------------
>>> [ 98.719012] precision 65536 too large
>>> [ 98.719039] WARNING: CPU: 1 PID: 3755 at lib/vsprintf.c:2703 vsnprintf+0x5e3/0x600
>>> ...
>>>
>>> URL: https://tracker.ceph.com/issues/55725
>>> Signed-off-by: Luís Henriques <lhenriques@...e.de>
>>> ---
>>> fs/ceph/mdsmap.c | 28 ++++++++++++++++++++++++----
>>> fs/ceph/xattr.c | 12 ++++++++----
>>> include/linux/ceph/mdsmap.h | 1 +
>>> 3 files changed, 33 insertions(+), 8 deletions(-)
>>>
>>> * Changes since v3
>>>
>>> As per Xiubo review:
>>> - Always force a (sync) SETXATTR Op when connecting to an old cluster
>>> - use '>' instead of '>='
>>> Also fixed the warning detected by 0day.
>>>
>>> * Changes since v2
>>>
>>> Well, a lot has changed since v2! Now the xattr max value setting is
>>> obtained through the mdsmap, which needs to be decoded, and the feature
>>> that was used in the previous revision was dropped. The drawback is that
>>> the MDS isn't unable to know in advance if a client is aware of this xattr
>>> max value.
>>>
>>> * Changes since v1
>>>
>>> Added support for new feature bit to get the MDS max_xattr_pairs_size
>>> setting.
>>>
>>> Also note that this patch relies on a patch that hasn't been merged yet
>>> ("ceph: use correct index when encoding client supported features"),
>>> otherwise the new feature bit won't be correctly encoded.
>>>
>>> diff --git a/fs/ceph/mdsmap.c b/fs/ceph/mdsmap.c
>>> index 30387733765d..c6ce83a48175 100644
>>> --- a/fs/ceph/mdsmap.c
>>> +++ b/fs/ceph/mdsmap.c
>>> @@ -13,6 +13,12 @@
>>> #include "super.h"
>>> +/*
>>> + * Maximum size of xattrs the MDS can handle per inode by default. This
>>> + * includes the attribute name and 4+4 bytes for the key/value sizes.
>>> + */
>>> +#define MDS_MAX_XATTR_SIZE (1<<16) /* 64K */
>> This macro makes no sense anymore, right ?
> Ah, yeah. That's still leftovers from the previous version.
>
>> I will merge this patch by removing this then.
> Thanks! Also... maybe you could also fix the (embarrassing) issue
> detected by 0day that I _tried_ to fix but failed (see below).
>
>> -- Xiubo
>>
>>
>>> +
>>> #define CEPH_MDS_IS_READY(i, ignore_laggy) \
>>> (m->m_info[i].state > 0 && ignore_laggy ? true : !m->m_info[i].laggy)
>>> @@ -352,12 +358,10 @@ struct ceph_mdsmap *ceph_mdsmap_decode(void **p, void
>>> *end, bool msgr2)
>>> __decode_and_drop_type(p, end, u8, bad_ext);
>>> }
>>> if (mdsmap_ev >= 8) {
>>> - u32 name_len;
>>> /* enabled */
>>> ceph_decode_8_safe(p, end, m->m_enabled, bad_ext);
>>> - ceph_decode_32_safe(p, end, name_len, bad_ext);
>>> - ceph_decode_need(p, end, name_len, bad_ext);
>>> - *p += name_len;
>>> + /* fs_name */
>>> + ceph_decode_skip_string(p, end, bad_ext);
>>> }
>>> /* damaged */
>>> if (mdsmap_ev >= 9) {
>>> @@ -370,6 +374,22 @@ struct ceph_mdsmap *ceph_mdsmap_decode(void **p, void *end, bool msgr2)
>>> } else {
>>> m->m_damaged = false;
>>> }
>>> + if (mdsmap_ev >= 17) {
>>> + /* balancer */
>>> + ceph_decode_skip_string(p, end, bad_ext);
>>> + /* standby_count_wanted */
>>> + ceph_decode_skip_32(p, end, bad_ext);
>>> + /* old_max_mds */
>>> + ceph_decode_skip_32(p, end, bad_ext);
>>> + /* min_compat_client */
>>> + ceph_decode_skip_8(p, end, bad_ext);
>>> + /* required_client_features */
>>> + ceph_decode_skip_set(p, end, 64, bad_ext);
>>> + ceph_decode_64_safe(p, end, m->m_max_xattr_size, bad_ext);
>>> + } else {
>>> + /* This forces the usage of the (sync) SETXATTR Op */
>>> + m->m_max_xattr_size = 0;
>>> + }
>>> bad_ext:
>>> dout("mdsmap_decode m_enabled: %d, m_damaged: %d, m_num_laggy: %d\n",
>>> !!m->m_enabled, !!m->m_damaged, m->m_num_laggy);
>>> diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c
>>> index 8c2dc2c762a4..1be415e9220b 100644
>>> --- a/fs/ceph/xattr.c
>>> +++ b/fs/ceph/xattr.c
>>> @@ -1086,7 +1086,7 @@ static int ceph_sync_setxattr(struct inode *inode, const char *name,
>>> flags |= CEPH_XATTR_REMOVE;
>>> }
>>> - dout("setxattr value=%.*s\n", (int)size, value);
>>> + dout("setxattr value size: %lu\n", size);
> This should be "%zu" and not "%lu". I'm OK sending v5 to fix these 2
> issues if you prefer.
Sure, please send a v5 for it.
>
> [ And then there's also the MDS-side which hasn't been merged yet. But
> this patch is probably worth in itself as it will change the client
> behavior to do the sync operation. ]
It's okay, this will fix this issue when we are connecting to old cephs,
and we could force to do the sync request always.
No need to wait the ceph PR.
-- Xiubo
>
> Cheers,
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