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adfs_dir_read() is only called from adfs_f_read(), so merge it into
that function. As new directories are always 2048 bytes in size,
(which we rely on elsewhere) we can consolidate some of the code.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Check that the lastmask and reserved fields are all zero, as per the
documentation.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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We have two locations where we validate the new directory format, so
factor this out to a helper.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Add and use pointers in the adfs_dir structure to access the directory
head and tail structures, which will always be contiguous in a buffer.
This allows us to avoid memcpy()ing the data in the new directory code,
making it slightly more efficient.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Rather than using setpos + getnext to iterate through the directory
entries, pass iterate() down to the dir format code to populate the
dirents.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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There is nothing in our readdir (aka iterate) method that relies on
the directory inode being exclusively locked, so switch to using the
iterate_shared() hook rather than iterate().
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Get rid of the ifdef, using IS_ENABLED() instead to detect whether the
code should be callable. This allows the compiler to always parse the
following code, reducing the chances of errors being missed.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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When we update a directory, a number of errors may happen. If we failed
to find the entry to update, we can just release the directory buffers
as normal.
However, if we have some other error, we may have partially updated the
buffers, resulting in an invalid directory. In this case, we need to
discard the buffers to avoid writing the contents back to the media, and
later re-read the directory from the media.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Use __u8 and pack the structures for on-disk directories.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Update directory locking such that it covers the validation of the
directory, which could fail if another thread is concurrently writing
to the same directory. Since we may sleep, we need to use a rwsem
rather than a rw spinlock.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Provide a helper for marking directory buffers dirty so they get
written back to disk.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Add a helper to read a directory using the inode, which we do in two
places.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Both directory formats code the mechanics of fetching the directory
buffers using their own implementations. Consolidate these into one
implementation.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Directories can span multiple buffers, and we currently open-code
memcpy access to these buffers, including dealing with entries that
are split across multiple buffers. Such code exists in both
directory format implementations.
Provide common functions to allow data to be copied from/to the
directory buffers as if they were a contiguous set of buffers, and
use them when accessing directories.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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adfs_fplus_sync() can be used for both directory formats since we now
have a common way to access the buffer heads, so move it into dir.c
and appropriately rename it. Remove the directory-format specific
implementations.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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With the bhs pointer in place, we have no need for separate per-format
free() methods, since a generic version will do. Provide a generic
implementation, remove the format specific implementations and the
method function pointer.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Initialise the dir object before we pass it down to the directory format
specific read handler. This allows us to get rid of the initialisation
inside those handlers.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Rename bh_fplus to bhs in preparation to make some of the directory
handling code sharable between implementations.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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When scanning the map for a fragment id, we need to keep track of the
free space links, so we don't inadvertently believe that the freespace
link is a valid fragment id.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Move map specific superblock initialisation to map.c, rather than
having it spread into super.c.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Use find_next_bit_le() to find the end of a fragment in the map rather
than open-coding this functionality.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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lookup_zone() and scan_free_map() cope in different ways with the
location of the map data within a zone:
1. lookup_zone() adds a four byte offset to the map data pointer to
skip over the check and free link bytes.
2. scan_free_map() needs to use the free link pointer, which is an
offset from itself, so we end up adding a 32-bit offset to the
end pointer (aka mapsize) which is really confusing.
Rename mapsize to endbit as this is really what it is, and incorporate
the 32-bit offset into the map layout. This means that both dm_startbit
and dm_endbit are now bit offsets from the start of the buffer, rather
than four bytes in to the buffer.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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We have several places which deal with releasing the map buffers and
freeing the map array. Provide a helper for this.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Split up adfs_read_map() into separate helpers to layout the map,
read the map, and release the map buffers.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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adfs_map_free() is not obvious whether it is freeing the map or
returning the number of free blocks on the filesystem. Rename it to
the more generic statfs() to make it clear that it's a statistic
function.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Keep all the map code together in map.c, rather than having some in
super.c
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Fix adfs_mode2atts() to actually update the file permissions on the
media rather than using the current inode mode. Note also that
directories do not have read/write permissions stored on the media.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Despite ADFS timestamps having centi-second granularity, and Linux
gaining fine-grained timestamp support in v2.5.48, fs/adfs was never
updated.
Update fs/adfs to centi-second support, and ensure that the inode ctime
always reflects what is written in underlying media.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Pull networking fixes from David Miller:
1) More jumbo frame fixes in r8169, from Heiner Kallweit.
2) Fix bpf build in minimal configuration, from Alexei Starovoitov.
3) Use after free in slcan driver, from Jouni Hogander.
4) Flower classifier port ranges don't work properly in the HW offload
case, from Yoshiki Komachi.
5) Use after free in hns3_nic_maybe_stop_tx(), from Yunsheng Lin.
6) Out of bounds access in mqprio_dump(), from Vladyslav Tarasiuk.
7) Fix flow dissection in dsa TX path, from Alexander Lobakin.
8) Stale syncookie timestampe fixes from Guillaume Nault.
[ Did an evil merge to silence a warning introduced by this pull - Linus ]
* git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net: (84 commits)
r8169: fix rtl_hw_jumbo_disable for RTL8168evl
net_sched: validate TCA_KIND attribute in tc_chain_tmplt_add()
r8169: add missing RX enabling for WoL on RTL8125
vhost/vsock: accept only packets with the right dst_cid
net: phy: dp83867: fix hfs boot in rgmii mode
net: ethernet: ti: cpsw: fix extra rx interrupt
inet: protect against too small mtu values.
gre: refetch erspan header from skb->data after pskb_may_pull()
pppoe: remove redundant BUG_ON() check in pppoe_pernet
tcp: Protect accesses to .ts_recent_stamp with {READ,WRITE}_ONCE()
tcp: tighten acceptance of ACKs not matching a child socket
tcp: fix rejected syncookies due to stale timestamps
lpc_eth: kernel BUG on remove
tcp: md5: fix potential overestimation of TCP option space
net: sched: allow indirect blocks to bind to clsact in TC
net: core: rename indirect block ingress cb function
net-sysfs: Call dev_hold always in netdev_queue_add_kobject
net: dsa: fix flow dissection on Tx path
net/tls: Fix return values to avoid ENOTSUPP
net: avoid an indirect call in ____sys_recvmsg()
...
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Pull more SCSI updates from James Bottomley:
"Eleven patches, all in drivers (no core changes) that are either minor
cleanups or small fixes.
They were late arriving, but still safe for -rc1"
* tag 'scsi-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
scsi: MAINTAINERS: Add the linux-scsi mailing list to the ISCSI entry
scsi: megaraid_sas: Make poll_aen_lock static
scsi: sd_zbc: Improve report zones error printout
scsi: qla2xxx: Fix qla2x00_request_irqs() for MSI
scsi: qla2xxx: unregister ports after GPN_FT failure
scsi: qla2xxx: fix rports not being mark as lost in sync fabric scan
scsi: pm80xx: Remove unused include of linux/version.h
scsi: pm80xx: fix logic to break out of loop when register value is 2 or 3
scsi: scsi_transport_sas: Fix memory leak when removing devices
scsi: lpfc: size cpu map by last cpu id set
scsi: ibmvscsi_tgt: Remove unneeded variable rc
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Pull cifs fixes from Steve French:
"Nine cifs/smb3 fixes:
- one fix for stable (oops during oplock break)
- two timestamp fixes including important one for updating mtime at
close to avoid stale metadata caching issue on dirty files (also
improves perf by using SMB2_CLOSE_FLAG_POSTQUERY_ATTRIB over the
wire)
- two fixes for "modefromsid" mount option for file create (now
allows mode bits to be set more atomically and accurately on create
by adding "sd_context" on create when modefromsid specified on
mount)
- two fixes for multichannel found in testing this week against
different servers
- two small cleanup patches"
* tag '5.5-rc-smb3-fixes-part2' of git://git.samba.org/sfrench/cifs-2.6:
smb3: improve check for when we send the security descriptor context on create
smb3: fix mode passed in on create for modetosid mount option
cifs: fix possible uninitialized access and race on iface_list
cifs: Fix lookup of SMB connections on multichannel
smb3: query attributes on file close
smb3: remove unused flag passed into close functions
cifs: remove redundant assignment to pointer pneg_ctxt
fs: cifs: Fix atime update check vs mtime
CIFS: Fix NULL-pointer dereference in smb2_push_mandatory_locks
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git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull misc vfs cleanups from Al Viro:
"No common topic, just three cleanups".
* 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
make __d_alloc() static
fs/namespace: add __user to open_tree and move_mount syscalls
fs/fnctl: fix missing __user in fcntl_rw_hint()
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Pull NTB update from Jon Mason:
"Just a simple patch to add a new Hygon Device ID to the AMD NTB device
driver"
* tag 'ntb-5.5' of git://github.com/jonmason/ntb:
NTB: Add Hygon Device ID
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git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input
Pull more input updates from Dmitry Torokhov:
- fixups for Synaptics RMI4 driver
- a quirk for Goodinx touchscreen on Teclast tablet
- a new keycode definition for activating privacy screen feature found
on a few "enterprise" laptops
- updates to snvs_pwrkey driver
- polling uinput device for writing (which is always allowed) now works
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input:
Input: synaptics-rmi4 - don't increment rmiaddr for SMBus transfers
Input: synaptics-rmi4 - re-enable IRQs in f34v7_do_reflash
Input: goodix - add upside-down quirk for Teclast X89 tablet
Input: add privacy screen toggle keycode
Input: uinput - fix returning EPOLLOUT from uinput_poll
Input: snvs_pwrkey - remove gratuitous NULL initializers
Input: snvs_pwrkey - send key events for i.MX6 S, DL and Q
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Pull iomap fixes from Darrick Wong:
"Fix a race condition and a use-after-free error:
- Fix a UAF when reporting writeback errors
- Fix a race condition when handling page uptodate on fragmented file
with blocksize < pagesize"
* tag 'iomap-5.5-merge-14' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux:
iomap: stop using ioend after it's been freed in iomap_finish_ioend()
iomap: fix sub-page uptodate handling
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Pull xfs fixes from Darrick Wong:
"Fix a couple of resource management errors and a hang:
- fix a crash in the log setup code when log mounting fails
- fix a hang when allocating space on the realtime device
- fix a block leak when freeing space on the realtime device"
* tag 'xfs-5.5-merge-17' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux:
xfs: fix mount failure crash on invalid iclog memory access
xfs: don't check for AG deadlock for realtime files in bunmapi
xfs: fix realtime file data space leak
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git://git.kernel.org/pub/scm/linux/kernel/git/hubcap/linux
Pull orangefs update from Mike Marshall:
"orangefs: posix open permission checking...
Orangefs has no open, and orangefs checks file permissions on each
file access. Posix requires that file permissions be checked on open
and nowhere else. Orangefs-through-the-kernel needs to seem posix
compliant.
The VFS opens files, even if the filesystem provides no method. We can
see if a file was successfully opened for read and or for write by
looking at file->f_mode.
When writes are flowing from the page cache, file is no longer
available. We can trust the VFS to have checked file->f_mode before
writing to the page cache.
The mode of a file might change between when it is opened and IO
commences, or it might be created with an arbitrary mode.
We'll make sure we don't hit EACCES during the IO stage by using
UID 0"
[ This is "posixish", but not a great solution in the long run, since a
proper secure network server shouldn't really trust the client like this.
But proper and secure POSIX behavior requires an open method and a
resulting cookie for IO of some kind, or similar. - Linus ]
* tag 'for-linus-5.5-ofs1' of git://git.kernel.org/pub/scm/linux/kernel/git/hubcap/linux:
orangefs: posix open permission checking...
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Pull nfsd updates from Bruce Fields:
"This is a relatively quiet cycle for nfsd, mainly various bugfixes.
Possibly most interesting is Trond's fixes for some callback races
that were due to my incomplete understanding of rpc client shutdown.
Unfortunately at the last minute I've started noticing a new
intermittent failure to send callbacks. As the logic seems basically
correct, I'm leaving Trond's patches in for now, and hope to find a
fix in the next week so I don't have to revert those patches"
* tag 'nfsd-5.5' of git://linux-nfs.org/~bfields/linux: (24 commits)
nfsd: depend on CRYPTO_MD5 for legacy client tracking
NFSD fixing possible null pointer derefering in copy offload
nfsd: check for EBUSY from vfs_rmdir/vfs_unink.
nfsd: Ensure CLONE persists data and metadata changes to the target file
SUNRPC: Fix backchannel latency metrics
nfsd: restore NFSv3 ACL support
nfsd: v4 support requires CRYPTO_SHA256
nfsd: Fix cld_net->cn_tfm initialization
lockd: remove __KERNEL__ ifdefs
sunrpc: remove __KERNEL__ ifdefs
race in exportfs_decode_fh()
nfsd: Drop LIST_HEAD where the variable it declares is never used.
nfsd: document callback_wq serialization of callback code
nfsd: mark cb path down on unknown errors
nfsd: Fix races between nfsd4_cb_release() and nfsd4_shutdown_callback()
nfsd: minor 4.1 callback cleanup
SUNRPC: Fix svcauth_gss_proxy_init()
SUNRPC: Trace gssproxy upcall results
sunrpc: fix crash when cache_head become valid before update
nfsd: remove private bin2hex implementation
...
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Pull NFS client updates from Trond Myklebust:
"Highlights include:
Features:
- NFSv4.2 now supports cross device offloaded copy (i.e. offloaded
copy of a file from one source server to a different target
server).
- New RDMA tracepoints for debugging congestion control and Local
Invalidate WRs.
Bugfixes and cleanups
- Drop the NFSv4.1 session slot if nfs4_delegreturn_prepare waits for
layoutreturn
- Handle bad/dead sessions correctly in nfs41_sequence_process()
- Various bugfixes to the delegation return operation.
- Various bugfixes pertaining to delegations that have been revoked.
- Cleanups to the NFS timespec code to avoid unnecessary conversions
between timespec and timespec64.
- Fix unstable RDMA connections after a reconnect
- Close race between waking an RDMA sender and posting a receive
- Wake pending RDMA tasks if connection fails
- Fix MR list corruption, and clean up MR usage
- Fix another RPCSEC_GSS issue with MIC buffer space"
* tag 'nfs-for-5.5-1' of git://git.linux-nfs.org/projects/trondmy/linux-nfs: (79 commits)
SUNRPC: Capture completion of all RPC tasks
SUNRPC: Fix another issue with MIC buffer space
NFS4: Trace lock reclaims
NFS4: Trace state recovery operation
NFSv4.2 fix memory leak in nfs42_ssc_open
NFSv4.2 fix kfree in __nfs42_copy_file_range
NFS: remove duplicated include from nfs4file.c
NFSv4: Make _nfs42_proc_copy_notify() static
NFS: Fallocate should use the nfs4_fattr_bitmap
NFS: Return -ETXTBSY when attempting to write to a swapfile
fs: nfs: sysfs: Remove NULL check before kfree
NFS: remove unneeded semicolon
NFSv4: add declaration of current_stateid
NFSv4.x: Drop the slot if nfs4_delegreturn_prepare waits for layoutreturn
NFSv4.x: Handle bad/dead sessions correctly in nfs41_sequence_process()
nfsv4: Move NFSPROC4_CLNT_COPY_NOTIFY to end of list
SUNRPC: Avoid RPC delays when exiting suspend
NFS: Add a tracepoint in nfs_fh_to_dentry()
NFSv4: Don't retry the GETATTR on old stateid in nfs4_delegreturn_done()
NFSv4: Handle NFS4ERR_OLD_STATEID in delegreturn
...
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We had cases in the previous patch where we were sending the security
descriptor context on SMB3 open (file create) in cases when we hadn't
mounted with with "modefromsid" mount option.
Add check for that mount flag before calling ad_sd_context in
open init.
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
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Pull VFIO updates from Alex Williamson:
- Remove hugepage checks for reserved pfns (Ben Luo)
- Fix irq-bypass unregister ordering (Jiang Yi)
* tag 'vfio-v5.5-rc1' of git://github.com/awilliam/linux-vfio:
vfio/pci: call irq_bypass_unregister_producer() before freeing irq
vfio/type1: remove hugepage checks in is_invalid_reserved_pfn()
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git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip
Pull more xen updates from Juergen Gross:
- a patch to fix a build warning
- a cleanup of no longer needed code in the Xen event handling
- a small series for the Xen grant driver avoiding high order
allocations and replacing an insane global limit by a per-call one
- a small series fixing Xen frontend/backend module referencing
* tag 'for-linus-5.5b-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
xen-blkback: allow module to be cleanly unloaded
xen/xenbus: reference count registered modules
xen/gntdev: switch from kcalloc() to kvcalloc()
xen/gntdev: replace global limit of mapped pages by limit per call
xen/gntdev: remove redundant non-zero check on ret
xen/events: remove event handling recursion detection
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Merge misc Kconfig updates from Andrew Morton:
"A number of changes to Kconfig files under lib/ from Changbin Du and
Krzysztof Kozlowski"
* emailed patches from Andrew Morton <akpm@linux-foundation.org>:
lib/: fix Kconfig indentation
kernel-hacking: move DEBUG_FS to 'Generic Kernel Debugging Instruments'
kernel-hacking: move DEBUG_BUGVERBOSE to 'printk and dmesg options'
kernel-hacking: create a submenu for scheduler debugging options
kernel-hacking: move SCHED_STACK_END_CHECK after DEBUG_STACK_USAGE
kernel-hacking: move Oops into 'Lockups and Hangs'
kernel-hacking: move kernel testing and coverage options to same submenu
kernel-hacking: group kernel data structures debugging together
kernel-hacking: create submenu for arch special debugging options
kernel-hacking: group sysrq/kgdb/ubsan into 'Generic Kernel Debugging Instruments'
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In referenced fix we removed the RTL8168e-specific jumbo config for
RTL8168evl in rtl_hw_jumbo_enable(). We have to do the same in
rtl_hw_jumbo_disable().
v2: fix referenced commit id
Fixes: 14012c9f3bb9 ("r8169: fix jumbo configuration for RTL8168evl")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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pipe_wait() may be simple, but since it relies on the pipe lock, it
means that we have to do the wakeup while holding the lock. That's
unfortunate, because the very first thing the waked entity will want to
do is to get the pipe lock for itself.
So get rid of the pipe_wait() usage by simply releasing the pipe lock,
doing the wakeup (if required) and then using wait_event_interruptible()
to wait on the right condition instead.
wait_event_interruptible() handles races on its own by comparing the
wakeup condition before and after adding itself to the wait queue, so
you can use an optimistic unlocked condition for it.
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Signed-off-by: Jiasen Lin <linjiasen@hygon.cn>
Signed-off-by: Jon Mason <jdmason@kudzu.us>
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This code is ancient, and goes back to when we only had a single page
for the pipe buffers. The exact history is hidden in the mists of time
(ie "before git", and in fact predates the BK repository too).
At that long-ago point in time, it actually helped to try to merge big
back-and-forth pipe reads and writes, and not limit pipe reads to the
single pipe buffer in length just because that was all we had at a time.
However, since then we've expanded the pipe buffers to multiple pages,
and this logic really doesn't seem to make sense. And a lot of it is
somewhat questionable (ie "hmm, the user asked for a non-blocking read,
but we see that there's a writer pending, so let's wait anyway to get
the extra data that the writer will have").
But more importantly, it makes the "go to sleep" logic much less
obvious, and considering the wakeup issues we've had, I want to make for
less of those kinds of things.
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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This is the read side version of the previous commit: it simplifies the
logic to only wake up waiting writers when necessary, and makes sure to
use a synchronous wakeup. This time not so much for GNU make jobserver
reasons (that pipe never fills up), but simply to get the writer going
quickly again.
A bit less verbose commentary this time, if only because I assume that
the write side commentary isn't going to be ignored if you touch this
code.
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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The pipe rework ends up having been extra painful, partly becaused of
actual bugs with ordering and caching of the pipe state, but also
because of subtle performance issues.
In particular, the pipe rework caused the kernel build to inexplicably
slow down.
The reason turns out to be that the GNU make jobserver (which limits the
parallelism of the build) uses a pipe to implement a "token" system: a
parallel submake will read a character from the pipe to get the job
token before starting a new job, and will write a character back to the
pipe when it is done. The overall job limit is thus easily controlled
by just writing the appropriate number of initial token characters into
the pipe.
But to work well, that really means that the old behavior of write
wakeups being synchronous (WF_SYNC) is very important - when the pipe
writer wakes up a reader, we want the reader to actually get scheduled
immediately. Otherwise you lose the parallelism of the build.
The pipe rework lost that synchronous wakeup on write, and we had
clearly all forgotten the reasons and rules for it.
This rewrites the pipe write wakeup logic to do the required Wsync
wakeups, but also clarifies the logic and avoids extraneous wakeups.
It also ends up addign a number of comments about what oit does and why,
so that we hopefully don't end up forgetting about this next time we
change this code.
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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