XFS has some inconsistent log message rate limiting with respect to
buffer alerts. The metadata I/O error notification uses the generic
ratelimited alert, the buffer push code uses a custom rate limit and
the similar quiesce time failure checks are not rate limited at all
(when they should be).
The custom rate limit defined in the buf item code is specifically
crafted for buffer alerts. It is more aggressive than generic rate
limiting code because it must accommodate a high frequency of I/O
error events in a relative short timeframe.
Factor out the custom rate limit state from the buf item code into a
per-buftarg rate limit so various alerts are limited based on the
target. Define a buffer alert helper function and use it for the
buffer alerts that are already ratelimited.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
The buffer write failure flag is intended to control the internal
write retry that XFS has historically implemented to help mitigate
the severity of transient I/O errors. The flag is set when a buffer
is resubmitted from the I/O completion path due to a previous
failure. It is checked on subsequent I/O completions to skip the
internal retry and fall through to the higher level configurable
error handling mechanism. The flag is cleared in the synchronous and
delwri submission paths and also checked in various places to log
write failure messages.
There are a couple minor problems with the current usage of this
flag. One is that we issue an internal retry after every submission
from xfsaild due to how delwri submission clears the flag. This
results in double the expected or configured number of write
attempts when under sustained failures. Another more subtle issue is
that the flag is never cleared on successful I/O completion. This
can cause xfs_wait_buftarg() to suggest that dirty buffers are being
thrown away due to the existence of the flag, when the reality is
that the flag might still be set because the write succeeded on the
retry.
Clear the write failure flag on successful I/O completion to address
both of these problems. This means that the internal retry attempt
occurs once since the last time a buffer write failed and that
various other contexts only see the flag set when the immediately
previous write attempt has failed.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
The shutdown check in xfs_iflush() duplicates checks down in the
buffer code. If the fs is shut down, xfs_trans_read_buf_map() always
returns an error and falls into the same error path. Remove the
unnecessary check along with the warning in xfs_imap_to_bp()
that generates excessive noise in the log if the fs is shut down.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
The inode flush code has several layers of error handling between
the inode and cluster flushing code. If the inode flush fails before
acquiring the backing buffer, the inode flush is aborted. If the
cluster flush fails, the current inode flush is aborted and the
cluster buffer is failed to handle the initial inode and any others
that might have been attached before the error.
Since xfs_iflush() is the only caller of xfs_iflush_cluster(), the
error handling between the two can be condensed in the top-level
function. If we update xfs_iflush_int() to always fall through to
the log item update and attach the item completion handler to the
buffer, any errors that occur after the first call to
xfs_iflush_int() can be handled with a buffer I/O failure.
Lift the error handling from xfs_iflush_cluster() into xfs_iflush()
and consolidate with the existing error handling. This also replaces
the need to release the buffer because failing the buffer with
XBF_ASYNC drops the current reference.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
We use the same buffer I/O failure code in a few different places.
It's not much code, but it's not necessarily self-explanatory.
Factor it into a helper and document it in one place.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Flush locked log items whose underlying buffers fail metadata
writeback are tagged with a special flag to indicate that the flush
lock is already held. This is currently implemented in the type
specific ->iop_push() callback, but the processing required for such
items is not type specific because we're only doing basic state
management on the underlying buffer.
Factor the failed log item handling out of the inode and dquot
->iop_push() callbacks and open code the buffer resubmit helper into
a single helper called from xfsaild_push_item(). This provides a
generic mechanism for handling failed metadata buffer writeback with
a bit less code.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Make sure we release resources properly if we cannot clean out the COW
extents in preparation for an extent swap.
Fixes: 96987eea53 ("xfs: cancel COW blocks before swapext")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
The functionality in xfs_diflags_to_linux() and xfs_diflags_to_iflags() are
nearly identical. The only difference is that *_to_linux() is called after
inode setup and disallows changing the DAX flag.
Combining them can be done with a flag which indicates if this is the initial
setup to allow the DAX flag to be properly set only at init time.
So remove xfs_diflags_to_linux() and call the modified xfs_diflags_to_iflags()
directly.
While we are here simplify xfs_diflags_to_iflags() to take struct xfs_inode and
use xfs_ip2xflags() to ensure future diflags are included correctly.
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
xfs_inode_supports_dax() should reflect if the inode can support DAX not
that it is enabled for DAX.
Change the use of xfs_inode_supports_dax() to reflect only if the inode
and underlying storage support dax.
Add a new function xfs_inode_should_enable_dax() which reflects if the
inode should be enabled for DAX.
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
An earlier call of xfs_reinit_inode() from xfs_iget_cache_hit() already
handles initialization of i_rwsem.
Doing so again is unneeded.
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Given how XFS is all based around btrees it doesn't make much sense
to offer a totally generic state when we can just use the btree cursor.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
All defer op instance place their own extension of the log item into
the dfp_done field. Replace that with a xfs_log_item to improve type
safety and make the code easier to follow.
Also use the opportunity to improve the ->finish_item calling conventions
to place the done log item as the higher level structure before the
list_entry used for the individual items.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Split out a helper that operates on a single xfs_defer_pending structure
to untangle the code.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
All defer op instance place their own extension of the log item into
the dfp_intent field. Replace that with a xfs_log_item to improve type
safety and make the code easier to follow.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
These are aways called together, and my merging them we reduce the amount
of indirect calls, improve type safety and in general clean up the code
a bit.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Create a helper that encapsulates the whole logic to create a defer
intent. This reorders some of the work that was done, but none of
that has an affect on the operation as only fields that don't directly
interact are affected.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Split out a xlog_add_buffer_cancelled helper which does the low-level
manipulation of the buffer cancelation table, and in that helper call
xlog_find_buffer_cancelled instead of open coding it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Don't bother to allocate memory and convert the log item when we
only need the block number and the length. Just extract them directly
and call xlog_buf_readahead separately in each branch.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Add a little helper to readahead a buffer if it hasn't been cancelled.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This list contains pretty much everything that is not a buffer. The
comment calls it item_list, which is a much better name than inode
list, so switch the actual variable name to that as well.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Replace the somewhat convoluted use of xlog_peek_buffer_cancelled and
xlog_check_buffer_cancelled with two obvious helpers:
xlog_is_buffer_cancelled, which returns true if there is a buffer in
the cancellation table, and
xlog_put_buffer_cancelled, which also decrements the reference count
of the buffer cancellation table.
Both share a little helper to look up the entry.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
There are a couple places where we directly call printk_once() and one
of them doesn't follow the standard xfs subsystem printk format as a
result.
#define printk_once variants to go with our existing printk_ratelimited
#defines so we can do one-shot printks in a consistent manner.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
I ran into a linker warning in XFS that originates from a mismatch
between libelf, binutils and objtool when certain files in the kernel
are built with "gcc -g":
x86_64-linux-ld: fs/xfs/xfs_trace.o: unable to initialize decompress status for section .debug_info
After some discussion, nobody could identify why xfs sets this flag
here. CONFIG_XFS_DEBUG used to enable lots of unrelated settings, but
now its main purpose is to enable extra consistency checks and assertions
that are unrelated to the debug info.
Remove the Makefile logic to set the flag here. If anyone relies
on the debug info, this can simply be enabled again with the global
CONFIG_DEBUG_INFO option.
Dave Chinner writes:
I'm pretty sure it was needed for the original kgdb integration back
in the early 2000s. That was when SGI used to patch their XFS dev
tree with kgdb and debug symbols were needed by the custom kgdb
modules that were ported across from the Irix kernel debugger.
ISTR that the early kcrash kernel dump analysis tools (again,
originated from the Irix "icrash" kernel dump tools) had custom XFS
debug scripts that needed also the debug info to work correctly...
Which is a long way of saying "we don't need it anymore" instead of
"nobody knows why it was set"... :)
Suggested-by: Christoph Hellwig <hch@infradead.org>
Link: https://lore.kernel.org/lkml/20200409074130.GD21033@infradead.org/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Since the "no-allocation" reservations has been removed, the resblks
value should be larger than zero, so remove the unnecessary check.
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
The check XFS_IS_QUOTA_RUNNING() has been done when enter the
xfs_qm_vop_create_dqattach() function, it will return directly
if the result is false, so the followed XFS_IS_QUOTA_RUNNING()
assertion is unnecessary. If we truly care about this, the check
also can be added to the condition of next if statements.
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
The initial value of variable udqp is NULL, and we only set the
flag XFS_QMOPT_PQUOTA in xfs_qm_vop_dqalloc() function, so only
the pdqp value is initialized and the udqp value is still NULL.
Since the udqp value is NULL in the rest part of xfs_ioctl_setattr()
function, it is meaningless and do nothing. So remove it from
xfs_ioctl_setattr().
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
We share an inode between gquota and pquota with the older
superblock that doesn't have separate pquotino, and for the
need_alloc == false case we don't need to call xfs_dir_ialloc()
function, so add the check if reserved free disk blocks is
needed.
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
When we're sorting recovered log items ahead of recovering them and
encounter a log item of unknown type, actually print the type code when
we're rejecting the whole transaction to aid in debugging.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Pull more btrfs fixes from David Sterba:
"A few more stability fixes, minor build warning fixes and git url
fixup:
- fix partial loss of prealloc extent past i_size after fsync
- fix potential deadlock due to wrong transaction handle passing via
journal_info
- fix gcc 4.8 struct intialization warning
- update git URL in MAINTAINERS entry"
* tag 'for-5.7-rc3-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux:
MAINTAINERS: btrfs: fix git repo URL
btrfs: fix gcc-4.8 build warning for struct initializer
btrfs: transaction: Avoid deadlock due to bad initialization timing of fs_info::journal_info
btrfs: fix partial loss of prealloc extent past i_size after fsync
Pull IOMMU fixes from Joerg Roedel:
- Fix a memory leak when dev_iommu gets freed and a sub-pointer does
not
- Build dependency fixes for Mediatek, spapr_tce, and Intel IOMMU
driver
- Export iommu_group_get_for_dev() only for GPLed modules
- Fix AMD IOMMU interrupt remapping when x2apic is enabled
- Fix error path in the QCOM IOMMU driver probe function
* tag 'iommu-fixes-v5.7-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu:
iommu/qcom: Fix local_base status check
iommu: Properly export iommu_group_get_for_dev()
iommu/vt-d: Use right Kconfig option name
iommu/amd: Fix legacy interrupt remapping for x2APIC-enabled system
iommu: spapr_tce: Disable compile testing to fix build on book3s_32 config
iommu/mediatek: Fix MTK_IOMMU dependencies
iommu: Fix the memory leak in dev_iommu_free()
The git repo listed for btrfs hasn't been updated in over a year.
List the current one instead.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Pull power management fixes from Rafael Wysocki:
- prevent the intel_pstate driver from printing excessive diagnostic
messages in some cases (Chris Wilson)
- make the hibernation restore kernel freeze kernel threads as well as
user space tasks (Dexuan Cui)
- fix the ACPI device PM disagnostic messages to include the correct
power state name (Kai-Heng Feng).
* tag 'pm-5.7-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
PM: ACPI: Output correct message on target power state
PM: hibernate: Freeze kernel threads in software_resume()
cpufreq: intel_pstate: Only mention the BIOS disabling turbo mode once
Pull iomap fix from Darrick Wong:
"Hoist the check for an unrepresentable FIBMAP return value into
ioctl_fibmap.
The internal kernel function can handle 64-bit values (and is needed
to fix a regression on ext4 + jbd2). It is only the userspace ioctl
that is so old that it cannot deal"
* tag 'iomap-5.7-fixes-1' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux:
fibmap: Warn and return an error in case of block > INT_MAX
Pull NFS client bugfixes from Trond Myklebust:
"Highlights include:
Stable fixes:
- fix handling of backchannel binding in BIND_CONN_TO_SESSION
Bugfixes:
- Fix a credential use-after-free issue in pnfs_roc()
- Fix potential posix_acl refcnt leak in nfs3_set_acl
- defer slow parts of rpc_free_client() to a workqueue
- Fix an Oopsable race in __nfs_list_for_each_server()
- Fix trace point use-after-free race
- Regression: the RDMA client no longer responds to server disconnect
requests
- Fix return values of xdr_stream_encode_item_{present, absent}
- _pnfs_return_layout() must always wait for layoutreturn completion
Cleanups:
- Remove unreachable error conditions"
* tag 'nfs-for-5.7-4' of git://git.linux-nfs.org/projects/trondmy/linux-nfs:
NFS: Fix a race in __nfs_list_for_each_server()
NFSv4.1: fix handling of backchannel binding in BIND_CONN_TO_SESSION
SUNRPC: defer slow parts of rpc_free_client() to a workqueue.
NFSv4: Remove unreachable error condition due to rpc_run_task()
SUNRPC: Remove unreachable error condition
xprtrdma: Fix use of xdr_stream_encode_item_{present, absent}
xprtrdma: Fix trace point use-after-free race
xprtrdma: Restore wake-up-all to rpcrdma_cm_event_handler()
nfs: Fix potential posix_acl refcnt leak in nfs3_set_acl
NFS/pnfs: Fix a credential use-after-free issue in pnfs_roc()
NFS/pnfs: Ensure that _pnfs_return_layout() waits for layoutreturn completion
Pull dmaengine fixes from Vinod Koul:
"Core:
- Documentation typo fixes
- fix the channel indexes
- dmatest: fixes for process hang and iterations
Drivers:
- hisilicon: build error fix without PCI_MSI
- ti-k3: deadlock fix
- uniphier-xdmac: fix for reg region
- pch: fix data race
- tegra: fix clock state"
* tag 'dmaengine-fix-5.7-rc4' of git://git.infradead.org/users/vkoul/slave-dma:
dmaengine: dmatest: Fix process hang when reading 'wait' parameter
dmaengine: dmatest: Fix iteration non-stop logic
dmaengine: tegra-apb: Ensure that clock is enabled during of DMA synchronization
dmaengine: fix channel index enumeration
dmaengine: mmp_tdma: Reset channel error on release
dmaengine: mmp_tdma: Do not ignore slave config validation errors
dmaengine: pch_dma.c: Avoid data race between probe and irq handler
dt-bindings: dma: uniphier-xdmac: switch to single reg region
include/linux/dmaengine: Typos fixes in API documentation
dmaengine: xilinx_dma: Add missing check for empty list
dmaengine: ti: k3-psil: fix deadlock on error path
dmaengine: hisilicon: Fix build error without PCI_MSI
Pull VFIO fixes from Alex Williamson:
- copy_*_user validity check for new vfio_dma_rw interface (Yan Zhao)
- Fix a potential math overflow (Yan Zhao)
- Use follow_pfn() for calculating PFNMAPs (Sean Christopherson)
* tag 'vfio-v5.7-rc4' of git://github.com/awilliam/linux-vfio:
vfio/type1: Fix VA->PA translation for PFNMAP VMAs in vaddr_get_pfn()
vfio: avoid possible overflow in vfio_iommu_type1_pin_pages
vfio: checking of validity of user vaddr in vfio_dma_rw
Pull arm64 fix from Catalin Marinas:
"Add -fasynchronous-unwind-tables to the vDSO CFLAGS"
* tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux:
arm64: vdso: Add -fasynchronous-unwind-tables to cflags
Pull io_uring fixes from Jens Axboe:
- Fix for statx not grabbing the file table, making AT_EMPTY_PATH fail
- Cover a few cases where async poll can handle retry, eliminating the
need for an async thread
- fallback request busy/free fix (Bijan)
- syzbot reported SQPOLL thread exit fix for non-preempt (Xiaoguang)
- Fix extra put of req for sync_file_range (Pavel)
- Always punt splice async. We'll improve this for 5.8, but wanted to
eliminate the inode mutex lock from the non-blocking path for 5.7
(Pavel)
* tag 'io_uring-5.7-2020-05-01' of git://git.kernel.dk/linux-block:
io_uring: punt splice async because of inode mutex
io_uring: check non-sync defer_list carefully
io_uring: fix extra put in sync_file_range()
io_uring: use cond_resched() in io_ring_ctx_wait_and_kill()
io_uring: use proper references for fallback_req locking
io_uring: only force async punt if poll based retry can't handle it
io_uring: enable poll retry for any file with ->read_iter / ->write_iter
io_uring: statx must grab the file table for valid fd
