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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
Implement support for unbuffered and DIO reads in the netfs library,
utilising the existing read helper code to do block splitting and
individual queuing. The code also handles extraction of the destination
buffer from the supplied iterator, allowing async unbuffered reads to take
place.
The read will be split up according to the rsize setting and, if supplied,
the ->clamp_length() method. Note that the next subrequest will be issued
as soon as issue_op returns, without waiting for previous ones to finish.
The network filesystem needs to pause or handle queuing them if it doesn't
want to fire them all at the server simultaneously.
Once all the subrequests have finished, the state will be assessed and the
amount of data to be indicated as having being obtained will be
determined. As the subrequests may finish in any order, if an intermediate
subrequest is short, any further subrequests may be copied into the buffer
and then abandoned.
In the future, this will also take care of doing an unbuffered read from
encrypted content, with the decryption being done by the library.
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
Modify the netfs_io_request struct to act as a point around which writes
can be coordinated. It represents and pins a range of pages that need
writing and a list of regions of dirty data in that range of pages.
If RMW is required, the original data can be downloaded into the bounce
buffer, decrypted if necessary, the modifications made, then the modified
data can be reencrypted/recompressed and sent back to the server.
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
Rename /proc/fs/fscache to "netfs" and make a symlink from fscache to that.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: Christian Brauner <christian@brauner.io>
cc: linux-fsdevel@vger.kernel.org
cc: linux-cachefs@redhat.com
