A rolling buffer is a series of folios held in a list of folio_queues. New
folios and folio_queue structs may be inserted at the head simultaneously
with spent ones being removed from the tail without the need for locking.
The rolling buffer includes an iov_iter and it has to be careful managing
this as the list of folio_queues is extended such that an oops doesn't
incurred because the iterator was pointing to the end of a folio_queue
segment that got appended to and then removed.
We need to use the mechanism twice, once for read and once for write, and,
in future patches, we will use a second rolling buffer to handle bounce
buffering for content encryption.
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20241216204124.3752367-6-dhowells@redhat.com
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
David Howells <dhowells@redhat.com> says:
Here are some miscellaneous fixes and changes for netfslib and the ceph and
nfs filesystems:
(1) Ignore silly-rename files from afs and nfs when building the header
archive in a kernel build.
(2) netfs: Fix the way read result collection applies results to folios
when each folio is being read by multiple subrequests and the results
come out of order.
(3) netfs: Fix ENOMEM handling in buffered reads.
(4) nfs: Fix an oops in nfs_netfs_init_request() when copying to the cache.
(5) cachefiles: Parse the "secctx" command immediately to get the correct
error rather than leaving it to the "bind" command.
(6) netfs: Remove a redundant smp_rmb(). This isn't a bug per se and
could be deferred.
(7) netfs: Fix missing barriers by using clear_and_wake_up_bit().
(8) netfs: Work around recursion in read retry by failing and abandoning
the retried subrequest if no I/O is performed.
[!] NOTE: This only works around the recursion problem if the
recursion keeps returning no data. If the server manages, say, to
repeatedly return a single byte of data faster than the retry
algorithm can complete, it will still recurse and the stack
overrun may still occur. Actually fixing this requires quite an
intrusive change which will hopefully make the next merge window.
(9) netfs: Fix the clearance of a folio_queue when unlocking the page if
we're going to want to subsequently send the queue for copying to the
cache (if, for example, we're using ceph).
(10) netfs: Fix the lack of cancellation of copy-to-cache when the cache
for a file is temporarily disabled (for example when a DIO write is
done to the file). This patch and (9) fix hangs with ceph.
With these patches, I can run xfstest -g quick to completion on ceph with a
local cache.
The patches can also be found here with a bonus cifs patch:
https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=netfs-fixes
* patches from https://lore.kernel.org/r/20241213135013.2964079-1-dhowells@redhat.com:
netfs: Fix is-caching check in read-retry
netfs: Fix the (non-)cancellation of copy when cache is temporarily disabled
netfs: Fix ceph copy to cache on write-begin
netfs: Work around recursion by abandoning retry if nothing read
netfs: Fix missing barriers by using clear_and_wake_up_bit()
netfs: Remove redundant use of smp_rmb()
cachefiles: Parse the "secctx" immediately
nfs: Fix oops in nfs_netfs_init_request() when copying to cache
netfs: Fix enomem handling in buffered reads
netfs: Fix non-contiguous donation between completed reads
kheaders: Ignore silly-rename files
Link: https://lore.kernel.org/r/20241213135013.2964079-1-dhowells@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
netfs: Fix is-caching check in read-retry
The read-retry code checks the NETFS_RREQ_COPY_TO_CACHE flag to determine
if there might be failed reads from the cache that need turning into reads
from the server, with the intention of skipping the complicated part if it
can. The code that set the flag, however, got lost during the read-side
rewrite.
Fix the check to see if the cache_resources are valid instead. The flag
can then be removed.
Fixes: ee4cdf7ba8 ("netfs: Speed up buffered reading")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/3752048.1734381285@warthog.procyon.org.uk
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
When the caching for a cookie is temporarily disabled (e.g. due to a DIO
write on that file), future copying to the cache for that file is disabled
until all fds open on that file are closed. However, if netfslib is using
the deprecated PG_private_2 method (such as is currently used by ceph), and
decides it wants to copy to the cache, netfs_advance_write() will just bail
at the first check seeing that the cache stream is unavailable, and
indicate that it dealt with all the content.
This means that we have no subrequests to provide notifications to drive
the state machine or even to pin the request and the request just gets
discarded, leaving the folios with PG_private_2 set.
Fix this by jumping directly to cancel the request if the cache is not
available. That way, we don't remove mark3 from the folio_queue list and
netfs_pgpriv2_cancel() will clean up the folios.
This was found by running the generic/013 xfstest against ceph with an
active cache and the "-o fsc" option passed to ceph. That would usually
hang
Fixes: ee4cdf7ba8 ("netfs: Speed up buffered reading")
Reported-by: Max Kellermann <max.kellermann@ionos.com>
Closes: https://lore.kernel.org/r/CAKPOu+_4m80thNy5_fvROoxBm689YtA0dZ-=gcmkzwYSY4syqw@mail.gmail.com/
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20241213135013.2964079-11-dhowells@redhat.com
cc: Jeff Layton <jlayton@kernel.org>
cc: Ilya Dryomov <idryomov@gmail.com>
cc: Xiubo Li <xiubli@redhat.com>
cc: netfs@lists.linux.dev
cc: ceph-devel@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
syzkaller reported recursion with a loop of three calls (netfs_rreq_assess,
netfs_retry_reads and netfs_rreq_terminated) hitting the limit of the stack
during an unbuffered or direct I/O read.
There are a number of issues:
(1) There is no limit on the number of retries.
(2) A subrequest is supposed to be abandoned if it does not transfer
anything (NETFS_SREQ_NO_PROGRESS), but that isn't checked under all
circumstances.
(3) The actual root cause, which is this:
if (atomic_dec_and_test(&rreq->nr_outstanding))
netfs_rreq_terminated(rreq, ...);
When we do a retry, we bump the rreq->nr_outstanding counter to
prevent the final cleanup phase running before we've finished
dispatching the retries. The problem is if we hit 0, we have to do
the cleanup phase - but we're in the cleanup phase and end up
repeating the retry cycle, hence the recursion.
Work around the problem by limiting the number of retries. This is based
on Lizhi Xu's patch[1], and makes the following changes:
(1) Replace NETFS_SREQ_NO_PROGRESS with NETFS_SREQ_MADE_PROGRESS and make
the filesystem set it if it managed to read or write at least one byte
of data. Clear this bit before issuing a subrequest.
(2) Add a ->retry_count member to the subrequest and increment it any time
we do a retry.
(3) Remove the NETFS_SREQ_RETRYING flag as it is superfluous with
->retry_count. If the latter is non-zero, we're doing a retry.
(4) Abandon a subrequest if retry_count is non-zero and we made no
progress.
(5) Use ->retry_count in both the write-side and the read-size.
[?] Question: Should I set a hard limit on retry_count in both read and
write? Say it hits 50, we always abandon it. The problem is that
these changes only mitigate the issue. As long as it made at least one
byte of progress, the recursion is still an issue. This patch
mitigates the problem, but does not fix the underlying cause. I have
patches that will do that, but it's an intrusive fix that's currently
pending for the next merge window.
The oops generated by KASAN looks something like:
BUG: TASK stack guard page was hit at ffffc9000482ff48 (stack is ffffc90004830000..ffffc90004838000)
Oops: stack guard page: 0000 [#1] PREEMPT SMP KASAN NOPTI
...
RIP: 0010:mark_lock+0x25/0xc60 kernel/locking/lockdep.c:4686
...
mark_usage kernel/locking/lockdep.c:4646 [inline]
__lock_acquire+0x906/0x3ce0 kernel/locking/lockdep.c:5156
lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5825
local_lock_acquire include/linux/local_lock_internal.h:29 [inline]
___slab_alloc+0x123/0x1880 mm/slub.c:3695
__slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3908
__slab_alloc_node mm/slub.c:3961 [inline]
slab_alloc_node mm/slub.c:4122 [inline]
kmem_cache_alloc_noprof+0x2a7/0x2f0 mm/slub.c:4141
radix_tree_node_alloc.constprop.0+0x1e8/0x350 lib/radix-tree.c:253
idr_get_free+0x528/0xa40 lib/radix-tree.c:1506
idr_alloc_u32+0x191/0x2f0 lib/idr.c:46
idr_alloc+0xc1/0x130 lib/idr.c:87
p9_tag_alloc+0x394/0x870 net/9p/client.c:321
p9_client_prepare_req+0x19f/0x4d0 net/9p/client.c:644
p9_client_zc_rpc.constprop.0+0x105/0x880 net/9p/client.c:793
p9_client_read_once+0x443/0x820 net/9p/client.c:1570
p9_client_read+0x13f/0x1b0 net/9p/client.c:1534
v9fs_issue_read+0x115/0x310 fs/9p/vfs_addr.c:74
netfs_retry_read_subrequests fs/netfs/read_retry.c:60 [inline]
netfs_retry_reads+0x153a/0x1d00 fs/netfs/read_retry.c:232
netfs_rreq_assess+0x5d3/0x870 fs/netfs/read_collect.c:371
netfs_rreq_terminated+0xe5/0x110 fs/netfs/read_collect.c:407
netfs_retry_reads+0x155e/0x1d00 fs/netfs/read_retry.c:235
netfs_rreq_assess+0x5d3/0x870 fs/netfs/read_collect.c:371
netfs_rreq_terminated+0xe5/0x110 fs/netfs/read_collect.c:407
netfs_retry_reads+0x155e/0x1d00 fs/netfs/read_retry.c:235
netfs_rreq_assess+0x5d3/0x870 fs/netfs/read_collect.c:371
...
netfs_rreq_terminated+0xe5/0x110 fs/netfs/read_collect.c:407
netfs_retry_reads+0x155e/0x1d00 fs/netfs/read_retry.c:235
netfs_rreq_assess+0x5d3/0x870 fs/netfs/read_collect.c:371
netfs_rreq_terminated+0xe5/0x110 fs/netfs/read_collect.c:407
netfs_retry_reads+0x155e/0x1d00 fs/netfs/read_retry.c:235
netfs_rreq_assess+0x5d3/0x870 fs/netfs/read_collect.c:371
netfs_rreq_terminated+0xe5/0x110 fs/netfs/read_collect.c:407
netfs_dispatch_unbuffered_reads fs/netfs/direct_read.c:103 [inline]
netfs_unbuffered_read fs/netfs/direct_read.c:127 [inline]
netfs_unbuffered_read_iter_locked+0x12f6/0x19b0 fs/netfs/direct_read.c:221
netfs_unbuffered_read_iter+0xc5/0x100 fs/netfs/direct_read.c:256
v9fs_file_read_iter+0xbf/0x100 fs/9p/vfs_file.c:361
do_iter_readv_writev+0x614/0x7f0 fs/read_write.c:832
vfs_readv+0x4cf/0x890 fs/read_write.c:1025
do_preadv fs/read_write.c:1142 [inline]
__do_sys_preadv fs/read_write.c:1192 [inline]
__se_sys_preadv fs/read_write.c:1187 [inline]
__x64_sys_preadv+0x22d/0x310 fs/read_write.c:1187
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
Fixes: ee4cdf7ba8 ("netfs: Speed up buffered reading")
Closes: https://syzkaller.appspot.com/bug?extid=1fc6f64c40a9d143cfb6
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20241108034020.3695718-1-lizhi.xu@windriver.com/ [1]
Link: https://lore.kernel.org/r/20241213135013.2964079-9-dhowells@redhat.com
Tested-by: syzbot+885c03ad650731743489@syzkaller.appspotmail.com
Suggested-by: Lizhi Xu <lizhi.xu@windriver.com>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: v9fs@lists.linux.dev
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Reported-by: syzbot+885c03ad650731743489@syzkaller.appspotmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Instead of storing an opaque string, call security_secctx_to_secid()
right in the "secctx" command handler and store only the numeric
"secid". This eliminates an unnecessary string allocation and allows
the daemon to receive errors when writing the "secctx" command instead
of postponing the error to the "bind" command handler. For example,
if the kernel was built without `CONFIG_SECURITY`, "bind" will return
`EOPNOTSUPP`, but the daemon doesn't know why. With this patch, the
"secctx" will instead return `EOPNOTSUPP` which is the right context
for this error.
This patch adds a boolean flag `have_secid` because I'm not sure if we
can safely assume that zero is the special secid value for "not set".
This appears to be true for SELinux, Smack and AppArmor, but since
this attribute is not documented, I'm unable to derive a stable
guarantee for that.
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20241209141554.638708-1-max.kellermann@ionos.com/
Link: https://lore.kernel.org/r/20241213135013.2964079-6-dhowells@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
When a read subrequest finishes, if it doesn't have sufficient coverage to
complete the folio(s) covering either side of it, it will donate the excess
coverage to the adjacent subrequests on either side, offloading
responsibility for unlocking the folio(s) covered to them.
Now, preference is given to donating down to a lower file offset over
donating up because that check is done first - but there's no check that
the lower subreq is actually contiguous, and so we can end up donating
incorrectly.
The scenario seen[1] is that an 8MiB readahead request spanning four 2MiB
folios is split into eight 1MiB subreqs (numbered 1 through 8). These
terminate in the order 1,6,2,5,3,7,4,8. What happens is:
- 1 donates to 2
- 6 donates to 5
- 2 completes, unlocking the first folio (with 1).
- 5 completes, unlocking the third folio (with 6).
- 3 donates to 4
- 7 donates to 4 incorrectly
- 4 completes, unlocking the second folio (with 3), but can't use
the excess from 7.
- 8 donates to 4, also incorrectly.
Fix this by preventing downward donation if the subreqs are not contiguous
(in the example above, 7 donates to 4 across the gap left by 5 and 6).
Reported-by: Shyam Prasad N <nspmangalore@gmail.com>
Closes: https://lore.kernel.org/r/CANT5p=qBwjBm-D8soFVVtswGEfmMtQXVW83=TNfUtvyHeFQZBA@mail.gmail.com/
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/526707.1733224486@warthog.procyon.org.uk/ [1]
Link: https://lore.kernel.org/r/20241213135013.2964079-3-dhowells@redhat.com
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Tell tar to ignore silly-rename files (".__afs*" and ".nfs*") when building
the header archive. These occur when a file that is open is unlinked
locally, but hasn't yet been closed. Such files are visible to the user
via the getdents() syscall and so programs may want to do things with them.
During the kernel build, such files may be made during the processing of
header files and the cleanup may get deferred by fput() which may result in
tar seeing these files when it reads the directory, but they may have
disappeared by the time it tries to open them, causing tar to fail with an
error. Further, we don't want to include them in the tarball if they still
exist.
With CONFIG_HEADERS_INSTALL=y, something like the following may be seen:
find: './kernel/.tmp_cpio_dir/include/dt-bindings/reset/.__afs2080': No such file or directory
tar: ./include/linux/greybus/.__afs3C95: File removed before we read it
The find warning doesn't seem to cause a problem.
Fix this by telling tar when called from in gen_kheaders.sh to exclude such
files. This only affects afs and nfs; cifs uses the Windows Hidden
attribute to prevent the file from being seen.
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20241213135013.2964079-2-dhowells@redhat.com
cc: Masahiro Yamada <masahiroy@kernel.org>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-kernel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Encoding file handles is usually performed by a filesystem >encode_fh()
method that may fail for various reasons.
The legacy users of exportfs_encode_fh(), namely, nfsd and
name_to_handle_at(2) syscall are ready to cope with the possibility
of failure to encode a file handle.
There are a few other users of exportfs_encode_{fh,fid}() that
currently have a WARN_ON() assertion when ->encode_fh() fails.
Relax those assertions because they are wrong.
The second linked bug report states commit 16aac5ad1f ("ovl: support
encoding non-decodable file handles") in v6.6 as the regressing commit,
but this is not accurate.
The aforementioned commit only increases the chances of the assertion
and allows triggering the assertion with the reproducer using overlayfs,
inotify and drop_caches.
Triggering this assertion was always possible with other filesystems and
other reasons of ->encode_fh() failures and more particularly, it was
also possible with the exact same reproducer using overlayfs that is
mounted with options index=on,nfs_export=on also on kernels < v6.6.
Therefore, I am not listing the aforementioned commit as a Fixes commit.
Backport hint: this patch will have a trivial conflict applying to
v6.6.y, and other trivial conflicts applying to stable kernels < v6.6.
Reported-by: syzbot+ec07f6f5ce62b858579f@syzkaller.appspotmail.com
Tested-by: syzbot+ec07f6f5ce62b858579f@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-unionfs/671fd40c.050a0220.4735a.024f.GAE@google.com/
Reported-by: Dmitry Safonov <dima@arista.com>
Closes: https://lore.kernel.org/linux-fsdevel/CAGrbwDTLt6drB9eaUagnQVgdPBmhLfqqxAf3F+Juqy_o6oP8uw@mail.gmail.com/
Cc: stable@vger.kernel.org
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20241219115301.465396-1-amir73il@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
