2022-09-22 14:08:57

by Dave Wysochanski

[permalink] [raw]
Subject: [PATCH v8 0/3] Convert NFS with fscache to the netfs API

This patchset converts NFS with fscache non-direct READ IO paths to
use the netfs API with a non-invasive approach. The existing NFS pgio
layer does not need extensive changes, and is the best way so far I've
found to address Trond's concerns about modifying the IO path [1] as
well as only enabling netfs when fscache is configured and enabled [2].
I have not attempted performance comparisions to address Chuck
Lever's concern [3] because we are not converting the non-fscache
enabled NFS IO paths to netfs.

The main patch to be reviewed is patch #3 which converts nfs_read_folio
and nfs_readahead. There are two main compatibility points with the
interface between the NFS READ IO path and netfs. First, NFS IO
interfaces are page based and netfs is request based (multiple page).
Thus, there's some accounting information collected to turn multiple
NFS READ RPC completions into a single netfs completion, and we have
to pass a pointer to this information through NFS pgio layer. Second,
the unlocking of pages of an NFS READ is handled inside netfs, which
requires a tiny bit of refactoring of the NFS read code.

Patch #4 removes the NFS fscache counters and also removes the "fsc:"
line from /proc/self/mountstats. I was not sure if we need to leave
that line in the mountstats file, and just leave the values at 0, or
we can remove it. For now I've removed it but if needed for ABI or
some other reason I can add back a "dummy" line with zeros.

In patch #5 I've removed the existing trace events because they no
longer have any meaning, and did not add any new ones since netfs
and fscache has many tracepoints. A future series may want to look
at some of the pgio layer tracepoints along with maybe one or two
related to NFS with fscache but for now it does not seem needed.

The patchset is based on 6.0-rc6 and has been pushed to github at:
https://github.com/DaveWysochanskiRH/kernel/commits/nfs-fscache-netfs
https://github.com/DaveWysochanskiRH/kernel/commit/b0467a2c39f3e8582660d073f9fa5c45ec2ca7f0


Changes since v7
================
- PATCH3: Free netfs memory if nfs_pageio_add_page() fails inside
nfs_netfs_issue_read()
- PATCH3: Clean up handling of READs completing with retryable and
non-retryable errors by removing unneeded nfs_netfs_read_done();
fixes oops in generic/303 with vers=4.2 and RHEL8 server due to
use-after-free of netfs structure
- PATCH3: Update patch header
- PATCH4 and PATCH5: new


Testing
=======
The patches are fairly stable as evidenced with xfstests generic with
various servers, both with and without fscache enabled, with no hangs
or crashes seen:
- hammerspace(pNFS flexfiles): NFS4.1, NFS4.2
- NetApp(pNFS filelayout): NFS3, NFS4.0, NFS4.1
- RHEL8: NFS3,NFS4.0,NFS4.2

The known issues are as follows:

1. Unit test setting rsize < readahead does not properly read from
fscache but re-reads data from the NFS server
* This will be fixed with another linux-cachefs [4] patch to resolve
"Stop read optimisation when folio removed from pagecache"
* Daire Byrne also verified the patch fixes his issue as well

2. "Cache volume key already in use" after xfstest runs
* xfstests (hammerspace with vers=4.2,fsc) shows the following on the
console after some tests:
"NFS: Cache volume key already in use (nfs,4.1,2,c50,cfe0100a,3,,,8000,100000,100000,bb8,ea60,7530,ea60,1)"
* This may be fixed with another patch [5] that is in progress

3. Daire Byrne reported a NULL pointer oops at cachefiles_prepare_write+0x28/0x90
* only reproduced on RHEL7.9 based NFS re-export server using fscache with upstream kernel plus
the previous patches
* may be a bug in netfs or cachefiles exposed by NFS patches
* harder to reproduce/debug but under investigation

[58710.346376] BUG: kernel NULL pointer dereference, address: 0000000000000008
[58710.371212] CPU: 12 PID: 9134 Comm: kworker/u129:0 Tainted: G E 6.0.0-2.dneg.x86_64 #1
...
[58710.389995] Workqueue: events_unbound netfs_rreq_write_to_cache_work [netfs]
[58710.397188] RIP: 0010:cachefiles_prepare_write+0x28/0x90 [cachefiles]
...
[58710.500316] Call Trace:
[58710.502894] <TASK>
[58710.505126] netfs_rreq_write_to_cache_work+0x11c/0x320 [netfs]
[58710.511201] process_one_work+0x217/0x3e0
[58710.515358] worker_thread+0x4a/0x3b0
[58710.519152] ? process_one_work+0x3e0/0x3e0
[58710.523467] kthread+0xd6/0x100
[58710.526740] ? kthread_complete_and_exit+0x20/0x20
[58710.531659] ret_from_fork+0x1f/0x30


References
==========
[1] https://lore.kernel.org/linux-nfs/[email protected]/
[2] https://lore.kernel.org/linux-nfs/[email protected]/
[3] https://marc.info/?l=linux-nfs&m=160597917525083&w=4
[4] https://www.mail-archive.com/[email protected]/msg03043.html
[5] https://marc.info/?l=linux-nfs&m=165962662200679&w=4

Dave Wysochanski (5):
NFS: Rename readpage_async_filler to nfs_pageio_add_page
NFS: Configure support for netfs when NFS fscache is configured
NFS: Convert buffered read paths to use netfs when fscache is enabled
NFS: Remove all NFSIOS_FSCACHE counters due to conversion to netfs API
NFS: Remove fscache specific trace points and NFS_INO_FSCACHE bit

fs/nfs/Kconfig | 1 +
fs/nfs/delegation.c | 2 +-
fs/nfs/dir.c | 2 +-
fs/nfs/fscache.c | 242 ++++++++++++++++++++++---------------
fs/nfs/fscache.h | 111 +++++++++++------
fs/nfs/inode.c | 8 +-
fs/nfs/internal.h | 11 +-
fs/nfs/iostat.h | 17 ---
fs/nfs/nfstrace.h | 91 --------------
fs/nfs/pagelist.c | 12 ++
fs/nfs/pnfs.c | 12 +-
fs/nfs/read.c | 110 +++++++++--------
fs/nfs/super.c | 11 --
fs/nfs/write.c | 2 +-
include/linux/nfs_fs.h | 35 ++++--
include/linux/nfs_iostat.h | 12 --
include/linux/nfs_page.h | 3 +
include/linux/nfs_xdr.h | 3 +
18 files changed, 335 insertions(+), 350 deletions(-)

--
2.31.1


2022-09-28 10:36:04

by Jeff Layton

[permalink] [raw]
Subject: Re: [PATCH v8 0/3] Convert NFS with fscache to the netfs API

On Thu, 2022-09-22 at 09:58 -0400, Dave Wysochanski wrote:
> This patchset converts NFS with fscache non-direct READ IO paths to
> use the netfs API with a non-invasive approach. The existing NFS pgio
> layer does not need extensive changes, and is the best way so far I've
> found to address Trond's concerns about modifying the IO path [1] as
> well as only enabling netfs when fscache is configured and enabled [2].
> I have not attempted performance comparisions to address Chuck
> Lever's concern [3] because we are not converting the non-fscache
> enabled NFS IO paths to netfs.
>
> The main patch to be reviewed is patch #3 which converts nfs_read_folio
> and nfs_readahead. There are two main compatibility points with the
> interface between the NFS READ IO path and netfs. First, NFS IO
> interfaces are page based and netfs is request based (multiple page).
> Thus, there's some accounting information collected to turn multiple
> NFS READ RPC completions into a single netfs completion, and we have
> to pass a pointer to this information through NFS pgio layer. Second,
> the unlocking of pages of an NFS READ is handled inside netfs, which
> requires a tiny bit of refactoring of the NFS read code.
>
> Patch #4 removes the NFS fscache counters and also removes the "fsc:"
> line from /proc/self/mountstats. I was not sure if we need to leave
> that line in the mountstats file, and just leave the values at 0, or
> we can remove it. For now I've removed it but if needed for ABI or
> some other reason I can add back a "dummy" line with zeros.
>
> In patch #5 I've removed the existing trace events because they no
> longer have any meaning, and did not add any new ones since netfs
> and fscache has many tracepoints. A future series may want to look
> at some of the pgio layer tracepoints along with maybe one or two
> related to NFS with fscache but for now it does not seem needed.
>
> The patchset is based on 6.0-rc6 and has been pushed to github at:
> https://github.com/DaveWysochanskiRH/kernel/commits/nfs-fscache-netfs
> https://github.com/DaveWysochanskiRH/kernel/commit/b0467a2c39f3e8582660d073f9fa5c45ec2ca7f0
>
>
> Changes since v7
> ================
> - PATCH3: Free netfs memory if nfs_pageio_add_page() fails inside
> nfs_netfs_issue_read()
> - PATCH3: Clean up handling of READs completing with retryable and
> non-retryable errors by removing unneeded nfs_netfs_read_done();
> fixes oops in generic/303 with vers=4.2 and RHEL8 server due to
> use-after-free of netfs structure
> - PATCH3: Update patch header
> - PATCH4 and PATCH5: new
>
>
> Testing
> =======
> The patches are fairly stable as evidenced with xfstests generic with
> various servers, both with and without fscache enabled, with no hangs
> or crashes seen:
> - hammerspace(pNFS flexfiles): NFS4.1, NFS4.2
> - NetApp(pNFS filelayout): NFS3, NFS4.0, NFS4.1
> - RHEL8: NFS3,NFS4.0,NFS4.2
>
> The known issues are as follows:
>
> 1. Unit test setting rsize < readahead does not properly read from
> fscache but re-reads data from the NFS server
> * This will be fixed with another linux-cachefs [4] patch to resolve
> "Stop read optimisation when folio removed from pagecache"
> * Daire Byrne also verified the patch fixes his issue as well
>
> 2. "Cache volume key already in use" after xfstest runs
> * xfstests (hammerspace with vers=4.2,fsc) shows the following on the
> console after some tests:
> "NFS: Cache volume key already in use (nfs,4.1,2,c50,cfe0100a,3,,,8000,100000,100000,bb8,ea60,7530,ea60,1)"
> * This may be fixed with another patch [5] that is in progress
>
> 3. Daire Byrne reported a NULL pointer oops at cachefiles_prepare_write+0x28/0x90
> * only reproduced on RHEL7.9 based NFS re-export server using fscache with upstream kernel plus
> the previous patches
> * may be a bug in netfs or cachefiles exposed by NFS patches
> * harder to reproduce/debug but under investigation
>
> [58710.346376] BUG: kernel NULL pointer dereference, address: 0000000000000008
> [58710.371212] CPU: 12 PID: 9134 Comm: kworker/u129:0 Tainted: G E 6.0.0-2.dneg.x86_64 #1
> ...
> [58710.389995] Workqueue: events_unbound netfs_rreq_write_to_cache_work [netfs]
> [58710.397188] RIP: 0010:cachefiles_prepare_write+0x28/0x90 [cachefiles]
> ...
> [58710.500316] Call Trace:
> [58710.502894] <TASK>
> [58710.505126] netfs_rreq_write_to_cache_work+0x11c/0x320 [netfs]
> [58710.511201] process_one_work+0x217/0x3e0
> [58710.515358] worker_thread+0x4a/0x3b0
> [58710.519152] ? process_one_work+0x3e0/0x3e0
> [58710.523467] kthread+0xd6/0x100
> [58710.526740] ? kthread_complete_and_exit+0x20/0x20
> [58710.531659] ret_from_fork+0x1f/0x30
>
>
> References
> ==========
> [1] https://lore.kernel.org/linux-nfs/[email protected]/
> [2] https://lore.kernel.org/linux-nfs/[email protected]/
> [3] https://marc.info/?l=linux-nfs&m=160597917525083&w=4
> [4] https://www.mail-archive.com/[email protected]/msg03043.html
> [5] https://marc.info/?l=linux-nfs&m=165962662200679&w=4
>
> Dave Wysochanski (5):
> NFS: Rename readpage_async_filler to nfs_pageio_add_page
> NFS: Configure support for netfs when NFS fscache is configured
> NFS: Convert buffered read paths to use netfs when fscache is enabled
> NFS: Remove all NFSIOS_FSCACHE counters due to conversion to netfs API
> NFS: Remove fscache specific trace points and NFS_INO_FSCACHE bit
>
> fs/nfs/Kconfig | 1 +
> fs/nfs/delegation.c | 2 +-
> fs/nfs/dir.c | 2 +-
> fs/nfs/fscache.c | 242 ++++++++++++++++++++++---------------
> fs/nfs/fscache.h | 111 +++++++++++------
> fs/nfs/inode.c | 8 +-
> fs/nfs/internal.h | 11 +-
> fs/nfs/iostat.h | 17 ---
> fs/nfs/nfstrace.h | 91 --------------
> fs/nfs/pagelist.c | 12 ++
> fs/nfs/pnfs.c | 12 +-
> fs/nfs/read.c | 110 +++++++++--------
> fs/nfs/super.c | 11 --
> fs/nfs/write.c | 2 +-
> include/linux/nfs_fs.h | 35 ++++--
> include/linux/nfs_iostat.h | 12 --
> include/linux/nfs_page.h | 3 +
> include/linux/nfs_xdr.h | 3 +
> 18 files changed, 335 insertions(+), 350 deletions(-)
>

Like seeing a net-negative diffstat!

I reviewed the 3rd patch and you can add my Reviewed-by: to the 4th and
5th patches as well.

Nice work, Dave!
--
Jeff Layton <[email protected]>