BugLink: https://bugs.launchpad.net/bugs/2076435
[ Upstream commit a81c98bfa40c11f8ea79b5a9b3f5fda73bfbb4d2 ]
Fix netfs_page_mkwrite() to check that folio->mapping is valid once it has
taken the folio lock (as filemap_page_mkwrite() does). Without this,
generic/247 occasionally oopses with something like the following:
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
RIP: 0010:trace_event_raw_event_netfs_folio+0x61/0xc0
...
Call Trace:
<TASK>
? __die_body+0x1a/0x60
? page_fault_oops+0x6e/0xa0
? exc_page_fault+0xc2/0xe0
? asm_exc_page_fault+0x22/0x30
? trace_event_raw_event_netfs_folio+0x61/0xc0
trace_netfs_folio+0x39/0x40
netfs_page_mkwrite+0x14c/0x1d0
do_page_mkwrite+0x50/0x90
do_pte_missing+0x184/0x200
__handle_mm_fault+0x42d/0x500
handle_mm_fault+0x121/0x1f0
do_user_addr_fault+0x23e/0x3c0
exc_page_fault+0xc2/0xe0
asm_exc_page_fault+0x22/0x30
This is due to the invalidate_inode_pages2_range() issued at the end of the
DIO write interfering with the mmap'd writes.
Fixes: 102a7e2c59 ("netfs: Allow buffered shared-writeable mmap through netfs_page_mkwrite()")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/780211.1719318546@warthog.procyon.org.uk
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: v9fs@lists.linux.dev
cc: linux-afs@lists.infradead.org
cc: linux-cifs@vger.kernel.org
cc: linux-mm@kvack.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Portia Stephens <portia.stephens@canonical.com>
Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>
BugLink: https://bugs.launchpad.net/bugs/2070337
[ Upstream commit c97f59e276d4e93480f29a70accbd0d7273cf3f5 ]
In netfs_perform_write(), when the file is marked NETFS_ICTX_WRITETHROUGH
or O_*SYNC or RWF_*SYNC was specified, write-through caching is performed
on a buffered file. When setting up for write-through, we flush any
conflicting writes in the region and wait for the write to complete,
failing if there's a write error to return.
The issue arises if we're writing at or above the EOF position because we
skip the flush and - more importantly - the wait. This becomes a problem
if there's a partial folio at the end of the file that is being written out
and we want to make a write to it too. Both the already-running write and
the write we start both want to clear the writeback mark, but whoever is
second causes a warning looking something like:
------------[ cut here ]------------
R=00000012: folio 11 is not under writeback
WARNING: CPU: 34 PID: 654 at fs/netfs/write_collect.c:105
...
CPU: 34 PID: 654 Comm: kworker/u386:27 Tainted: G S ...
...
Workqueue: events_unbound netfs_write_collection_worker
...
RIP: 0010:netfs_writeback_lookup_folio
Fix this by making the flush-and-wait unconditional. It will do nothing if
there are no folios in the pagecache and will return quickly if there are
no folios in the region specified.
Further, move the WBC attachment above the flush call as the flush is going
to attach a WBC and detach it again if it is not present - and since we
need one anyway we might as well share it.
Fixes: 41d8e7673a ("netfs: Implement a write-through caching option")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202404161031.468b84f-oliver.sang@intel.com
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/2150448.1714130115@warthog.procyon.org.uk
Reviewed-by: Jeffrey Layton <jlayton@kernel.org>
cc: Eric Van Hensbergen <ericvh@kernel.org>
cc: Latchesar Ionkov <lucho@ionkov.net>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Christian Schoenebeck <linux_oss@crudebyte.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
cc: v9fs@lists.linux.dev
cc: linux-afs@lists.infradead.org
cc: linux-cifs@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Manuel Diewald <manuel.diewald@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Pull netfs updates from Christian Brauner:
"This extends the netfs helper library that network filesystems can use
to replace their own implementations. Both afs and 9p are ported. cifs
is ready as well but the patches are way bigger and will be routed
separately once this is merged. That will remove lots of code as well.
The overal goal is to get high-level I/O and knowledge of the page
cache and ouf of the filesystem drivers. This includes knowledge about
the existence of pages and folios
The pull request converts afs and 9p. This removes about 800 lines of
code from afs and 300 from 9p. For 9p it is now possible to do writes
in larger than a page chunks. Additionally, multipage folio support
can be turned on for 9p. Separate patches exist for cifs removing
another 2000+ lines. I've included detailed information in the
individual pulls I took.
Summary:
- Add NFS-style (and Ceph-style) locking around DIO vs buffered I/O
calls to prevent these from happening at the same time.
- Support for direct and unbuffered I/O.
- Support for write-through caching in the page cache.
- O_*SYNC and RWF_*SYNC writes use write-through rather than writing
to the page cache and then flushing afterwards.
- Support for write-streaming.
- Support for write grouping.
- Skip reads for which the server could only return zeros or EOF.
- The fscache module is now part of the netfs library and the
corresponding maintainer entry is updated.
- Some helpers from the fscache subsystem are renamed to mark them as
belonging to the netfs library.
- Follow-up fixes for the netfs library.
- Follow-up fixes for the 9p conversion"
* tag 'vfs-6.8.netfs' of gitolite.kernel.org:pub/scm/linux/kernel/git/vfs/vfs: (50 commits)
netfs: Fix wrong #ifdef hiding wait
cachefiles: Fix signed/unsigned mixup
netfs: Fix the loop that unmarks folios after writing to the cache
netfs: Fix interaction between write-streaming and cachefiles culling
netfs: Count DIO writes
netfs: Mark netfs_unbuffered_write_iter_locked() static
netfs: Fix proc/fs/fscache symlink to point to "netfs" not "../netfs"
netfs: Rearrange netfs_io_subrequest to put request pointer first
9p: Use length of data written to the server in preference to error
9p: Do a couple of cleanups
9p: Fix initialisation of netfs_inode for 9p
cachefiles: Fix __cachefiles_prepare_write()
9p: Use netfslib read/write_iter
afs: Use the netfs write helpers
netfs: Export the netfs_sreq tracepoint
netfs: Optimise away reads above the point at which there can be no data
netfs: Implement a write-through caching option
netfs: Provide a launder_folio implementation
netfs: Provide a writepages implementation
netfs, cachefiles: Pass upper bound length to allow expansion
...
In the loop in netfs_rreq_unmark_after_write() that removes the PG_fscache
from folios after they've been written to the cache, as soon as we remove
the mark from a multipage folio, it can get split - and then we might see a
fragment of folio again.
Guard against this by advancing the 'unlocked' tracker to the index of the
last page in the folio to avoid a double removal of the PG_fscache mark.
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: linux-afs@lists.infradead.org
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
An issue can occur between write-streaming (storing dirty data in partial
non-uptodate pages) and a cachefiles object being culled to make space.
The problem occurs because the cache object is only marked in use while
there are files open using it. Once it has been released, it can be culled
and the cookie marked disabled.
At this point, a streaming write is permitted to occur (if the cache is
active, we require pages to be prefetched and cached), but the cache can
become active again before this gets flushed out - and then two effects can
occur:
(1) The cache may be asked to write out a region that's less than its DIO
block size (assumed by cachefiles to be PAGE_SIZE) - and this causes
one of two debugging statements to be emitted.
(2) netfs_how_to_modify() gets confused because it sees a page that isn't
allowed to be non-uptodate being uptodate and tries to prefetch it -
leading to a warning that PG_fscache is set twice.
Fix this by the following means:
(1) Add a netfs_inode flag to disallow write-streaming to an inode and set
it if we ever do local caching of that inode. It remains set for the
lifetime of that inode - even if the cookie becomes disabled.
(2) If the no-write-streaming flag is set, then make netfs_how_to_modify()
always want to prefetch instead.
(3) If netfs_how_to_modify() decides it wants to prefetch a folio, but
that folio has write-streamed data in it, then it requires the folio
be flushed first.
(4) Export a counter of the number of times we wanted to prefetch a
non-uptodate page, but found it had write-streamed data in it.
(5) Export a counter of the number of times we cancelled a write to the
cache because it didn't DIO align and remove the debug statements.
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-erofs@lists.ozlabs.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Track the file position above which the server is not expected to have any
data (the "zero point") and preemptively assume that we can satisfy
requests by filling them with zeroes locally rather than attempting to
download them if they're over that line - even if we've written data back
to the server. Assume that any data that was written back above that
position is held in the local cache. Note that we have to split requests
that straddle the line.
Make use of this to optimise away some reads from the server. We need to
set the zero point in the following circumstances:
(1) When we see an extant remote inode and have no cache for it, we set
the zero_point to i_size.
(2) On local inode creation, we set zero_point to 0.
(3) On local truncation down, we reduce zero_point to the new i_size if
the new i_size is lower.
(4) On local truncation up, we don't change zero_point.
(5) On local modification, we don't change zero_point.
(6) On remote invalidation, we set zero_point to the new i_size.
(7) If stored data is discarded from the pagecache or culled from fscache,
we must set zero_point above that if the data also got written to the
server.
(8) If dirty data is written back to the server, but not fscache, we must
set zero_point above that.
(9) If a direct I/O write is made, set zero_point above that.
Assuming the above, any read from the server at or above the zero_point
position will return all zeroes.
The zero_point value can be stored in the cache, provided the above rules
are applied to it by any code that culls part of the local cache.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Provide a flag whereby a filesystem may request that cifs_perform_write()
perform write-through caching. This involves putting pages directly into
writeback rather than dirty and attaching them to a write operation as we
go.
Further, the writes being made are limited to the byte range being written
rather than whole folios being written. This can be used by cifs, for
example, to deal with strict byte-range locking.
This can't be used with content encryption as that may require expansion of
the write RPC beyond the write being made.
This doesn't affect writes via mmap - those are written back in the normal
way; similarly failed writethrough writes are marked dirty and left to
writeback to retry. Another option would be to simply invalidate them, but
the contents can be simultaneously accessed by read() and through mmap.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Institute a netfs write helper, netfs_file_write_iter(), to be pointed at
by the network filesystem ->write_iter() call. Make it handled buffered
writes by calling the previously defined netfs_perform_write() to copy the
source data into the pagecache.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Provide a netfs write helper, netfs_perform_write() to buffer data to be
written in the pagecache and mark the modified folios dirty.
It will perform "streaming writes" for folios that aren't currently
resident, if possible, storing data in partially modified folios that are
marked dirty, but not uptodate. It will also tag pages as belonging to
fs-specific write groups if so directed by the filesystem.
This is derived from generic_perform_write(), but doesn't use
->write_begin() and ->write_end(), having that logic rolled in instead.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Matthew Wilcox (Oracle)
Yang Shi
David Howells
Dan Carpenter
Linus Torvalds