Factor the loop body of xfsaild_push() into a separate
xfsaild_process_logitem() helper to improve readability.
This is a pure code movement with no functional change.
Signed-off-by: Yuto Ohnuki <ytohnuki@amazon.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
After xfsaild_push_item() calls iop_push(), the log item may have been
freed if the AIL lock was dropped during the push. Background inode
reclaim or the dquot shrinker can free the log item while the AIL lock
is not held, and the tracepoints in the switch statement dereference
the log item after iop_push() returns.
Fix this by capturing the log item type, flags, and LSN before calling
xfsaild_push_item(), and introducing a new xfs_ail_push_class trace
event class that takes these pre-captured values and the ailp pointer
instead of the log item pointer.
Reported-by: syzbot+652af2b3c5569c4ab63c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=652af2b3c5569c4ab63c
Fixes: 90c60e1640 ("xfs: xfs_iflush() is no longer necessary")
Cc: stable@vger.kernel.org # v5.9
Signed-off-by: Yuto Ohnuki <ytohnuki@amazon.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
This is the result of running the Coccinelle script from
scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
avoid scalar types (which need careful case-by-case checking), and
instead replace kmalloc-family calls that allocate struct or union
object instances:
Single allocations: kmalloc(sizeof(TYPE), ...)
are replaced with: kmalloc_obj(TYPE, ...)
Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...)
are replaced with: kmalloc_objs(TYPE, COUNT, ...)
Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...)
are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...)
(where TYPE may also be *VAR)
The resulting allocations no longer return "void *", instead returning
"TYPE *".
Signed-off-by: Kees Cook <kees@kernel.org>
The xfs.h header conflicts with the public xfs.h in xfsprogs, leading
to a spurious difference in all shared libxfs files that have to
include libxfs_priv.h in userspace. Directly include xfs_platform.h so
that we can add a header of the same name to xfsprogs and remove this
major annoyance for the shared code.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Don't pass expr to XFS_TEST_ERROR. Most calls pass a constant false,
and the places that do pass an expression become cleaner by moving it
out.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
This function doesn't take the AIL lock, but should be called
with AIL lock held. Also (hopefuly) simplify the comment.
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chandan Babu R <chandanbabu@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Marking a log item as failed kept a buffer reference around for
resubmission of inode and dquote items.
For inode items commit 298f7bec50 ("xfs: pin inode backing buffer to
the inode log item") started pinning the inode item buffers
unconditionally and removed the need for this. Later commit acc8f8628c
("xfs: attach dquot buffer to dquot log item buffer") did the same for
dquot items but didn't fully clean up the xfs_clear_li_failed side
for them. Stop adding the extra pin for dquot items and remove the
helpers.
This happens to fix a call to xfs_buf_free with the AIL lock held,
which would be incorrect for the unlikely case freeing the buffer
ends up calling vfree.
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Since commit acc8f8628c ("xfs: attach dquot buffer to dquot log item
buffer") all buf items that use bp->b_li_list are explicitly checked for
in the branch to just clears XFS_LI_FAILED. Remove the dead arm that
calls xfs_clear_li_failed.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Acked-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Ever since 6.12-rc1, I've observed a pile of warnings from the kernel
when running fstests with quotas enabled:
WARNING: CPU: 1 PID: 458580 at mm/page_alloc.c:4221 __alloc_pages_noprof+0xc9c/0xf18
CPU: 1 UID: 0 PID: 458580 Comm: xfsaild/sda3 Tainted: G W 6.12.0-rc6-djwa #rc6 6ee3e0e531f6457e2d26aa008a3b65ff184b377c
<snip>
Call trace:
__alloc_pages_noprof+0xc9c/0xf18
alloc_pages_mpol_noprof+0x94/0x240
alloc_pages_noprof+0x68/0xf8
new_slab+0x3e0/0x568
___slab_alloc+0x5a0/0xb88
__slab_alloc.constprop.0+0x7c/0xf8
__kmalloc_noprof+0x404/0x4d0
xfs_buf_get_map+0x594/0xde0 [xfs 384cb02810558b4c490343c164e9407332118f88]
xfs_buf_read_map+0x64/0x2e0 [xfs 384cb02810558b4c490343c164e9407332118f88]
xfs_trans_read_buf_map+0x1dc/0x518 [xfs 384cb02810558b4c490343c164e9407332118f88]
xfs_qm_dqflush+0xac/0x468 [xfs 384cb02810558b4c490343c164e9407332118f88]
xfs_qm_dquot_logitem_push+0xe4/0x148 [xfs 384cb02810558b4c490343c164e9407332118f88]
xfsaild+0x3f4/0xde8 [xfs 384cb02810558b4c490343c164e9407332118f88]
kthread+0x110/0x128
ret_from_fork+0x10/0x20
---[ end trace 0000000000000000 ]---
This corresponds to the line:
WARN_ON_ONCE(current->flags & PF_MEMALLOC);
within the NOFAIL checks. What's happening here is that the XFS AIL is
trying to write a disk quota update back into the filesystem, but for
that it needs to read the ondisk buffer for the dquot. The buffer is
not in memory anymore, probably because it was evicted. Regardless, the
buffer cache tries to allocate a new buffer, but those allocations are
NOFAIL. The AIL thread has marked itself PF_MEMALLOC (aka noreclaim)
since commit 43ff2122e6 ("xfs: on-stack delayed write buffer lists")
presumably because reclaim can push on XFS to push on the AIL.
An easy way to fix this probably would have been to drop the NOFAIL flag
from the xfs_buf allocation and open code a retry loop, but then there's
still the problem that for bs>ps filesystems, the buffer itself could
require up to 64k worth of pages.
Inode items had similar behavior (multi-page cluster buffers that we
don't want to allocate in the AIL) which we solved by making transaction
precommit attach the inode cluster buffers to the dirty log item. Let's
solve the dquot problem in the same way.
So: Make a real precommit handler to read the dquot buffer and attach it
to the log item; pass it to dqflush in the push method; and have the
iodone function detach the buffer once we've flushed everything. Add a
state flag to the log item to track when a thread has entered the
precommit -> push mechanism to skip the detaching if it turns out that
the dquot is very busy, as we don't hold the dquot lock between log item
commit and AIL push).
Reading and attaching the dquot buffer in the precommit hook is inspired
by the work done for inode cluster buffers some time ago.
Cc: <stable@vger.kernel.org> # v6.12
Fixes: 903edea6c5 ("mm: warn about illegal __GFP_NOFAIL usage in a more appropriate location and manner")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
In commit 9adf40249e, we changed the behavior of the AIL thread to
set its own task state to KILLABLE whenever the timeout value is
nonzero. Unfortunately, this missed the fact that xfsaild_push will
return 50ms (aka a longish sleep) when we reach the push target or the
AIL becomes empty, so xfsaild goes to sleep for a long period of time in
uninterruptible D state.
This results in artificially high load averages because KILLABLE
processes are UNINTERRUPTIBLE, which contributes to load average even
though the AIL is asleep waiting for someone to interrupt it. It's not
blocked on IOs or anything, but people scrap ps for processes that look
like they're stuck in D state, so restore the previous threshold.
Fixes: 9adf40249e ("xfs: AIL doesn't need manual pushing")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
The AIL pushing code spends a huge amount of time skipping over
items that are already marked as flushing. It is not uncommon to
see hundreds of thousands of items skipped every second due to inode
clustering marking all the inodes in a cluster as flushing when the
first one is flushed.
However, to discover an item is already flushing and should be
skipped we have to call the iop_push() method for it to try to flush
the item. For inodes (where this matters most), we have to first
check that inode is flushable first.
We can optimise this overhead away by tracking whether the log item
is flushing internally. This allows xfsaild_push() to check the log
item directly for flushing state and immediately skip the log item.
Whilst this doesn't remove the CPU cache misses for loading the log
item, it does avoid the overhead of an indirect function call
and the cache misses involved in accessing inode and
backing cluster buffer structures to determine flushing state. When
trying to flush hundreds of thousands of inodes each second, this
CPU overhead saving adds up quickly.
It's so noticeable that the biggest issue with pushing on the AIL on
fast storage becomes the 10ms back-off wait when we hit enough
pinned buffers to break out of the push loop but not enough for the
AIL pushing to be considered stuck. This limits the xfsaild to about
70% total CPU usage, and on fast storage this isn't enough to keep
the storage 100% busy.
The xfsaild will block on IO submission on slow storage and so is
self throttling - it does not need a backoff in the case where we
are really just breaking out of the walk to submit the IO we have
gathered.
Further with no backoff we don't need to gather huge delwri lists to
mitigate the impact of backoffs, so we can submit IO more frequently
and reduce the time log items spend in flushing state by breaking
out of the item push loop once we've gathered enough IO to batch
submission effectively.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
Currently we track space used in the log by grant heads.
These store the reserved space as a physical log location and
combine both space reserved for future use with space already used in
the log in a single variable. The amount of space consumed in the
log is then calculated as the distance between the log tail and
the grant head.
The problem with tracking the grant head as a physical location
comes from the fact that it tracks both log cycle count and offset
into the log in bytes in a single 64 bit variable. because the cycle
count on disk is a 32 bit number, this also limits the offset into
the log to 32 bits. ANd because that is in bytes, we are limited to
being able to track only 2GB of log space in the grant head.
Hence to support larger physical logs, we need to track used space
differently in the grant head. We no longer use the grant head for
guiding AIL pushing, so the only thing it is now used for is
determining if we've run out of reservation space via the
calculation in xlog_space_left().
What we really need to do is move the grant heads away from tracking
physical space in the log. The issue here is that space consumed in
the log is not directly tracked by the current mechanism - the
space consumed in the log by grant head reservations gets returned
to the free pool by the tail of the log moving forward. i.e. the
space isn't directly tracked or calculated, but the used grant space
gets "freed" as the physical limits of the log are updated without
actually needing to update the grant heads.
Hence to move away from implicit, zero-update log space tracking we
need to explicitly track the amount of physical space the log
actually consumes separately to the in-memory reservations for
operations that will be committed to the journal. Luckily, we
already track the information we need to calculate this in the AIL
itself.
That is, the space currently consumed by the journal is the maximum
LSN that the AIL has seen minus the current log tail. As we update
both of these items dynamically as the head and tail of the log
moves, we always know exactly how much space the journal consumes.
This means that we also know exactly how much space the currently
active reservations require, and exactly how much free space we have
remaining for new reservations to be made. Most importantly, we know
what these spaces are indepedently of the physical locations of
the head and tail of the log.
Hence by separating out the physical space consumed by the journal,
we can now track reservations in the grant heads purely as a byte
count, and the log can be considered full when the tail space +
reservation space exceeds the size of the log. This means we can use
the full 64 bits of grant head space for reservation space,
completely removing the 32 bit byte count limitation on log size
that they impose.
Hence the first step in this conversion is to track and update the
"log tail space" every time the AIL tail or maximum seen LSN
changes.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
The current implementation of xlog_assign_tail_lsn() assumes that
when the AIL is empty, the log tail matches the LSN of the last
written commit record. This is recorded in xlog_state_set_callback()
as log->l_last_sync_lsn when the iclog state changes to
XLOG_STATE_CALLBACK. This change is then immediately followed by
running the callbacks on the iclog which then insert the log items
into the AIL at the "commit lsn" of that checkpoint.
The AIL tracks log items via the start record LSN of the checkpoint,
not the commit record LSN. This is because we can pipeline multiple
checkpoints, and so the start record of checkpoint N+1 can be
written before the commit record of checkpoint N. i.e:
start N commit N
+-------------+------------+----------------+
start N+1 commit N+1
The tail of the log cannot be moved to the LSN of commit N when all
the items of that checkpoint are written back, because then the
start record for N+1 is no longer in the active portion of the log
and recovery will fail/corrupt the filesystem.
Hence when all the log items in checkpoint N are written back, the
tail of the log most now only move as far forwards as the start LSN
of checkpoint N+1.
Hence we cannot use the maximum start record LSN the AIL sees as a
replacement the pointer to the current head of the on-disk log
records. However, we currently only use the l_last_sync_lsn when the
AIL is empty - when there is no start LSN remaining, the tail of the
log moves to the LSN of the last commit record as this is where
recovery needs to start searching for recoverable records. THe next
checkpoint will have a start record LSN that is higher than
l_last_sync_lsn, and so everything still works correctly when new
checkpoints are written to an otherwise empty log.
l_last_sync_lsn is an atomic variable because it is currently
updated when an iclog with callbacks attached moves to the CALLBACK
state. While we hold the icloglock at this point, we don't hold the
AIL lock. When we assign the log tail, we hold the AIL lock, not the
icloglock because we have to look up the AIL. Hence it is an atomic
variable so it's not bound to a specific lock context.
However, the iclog callbacks are only used for CIL checkpoints. We
don't use callbacks with unmount record writes, so the
l_last_sync_lsn variable only gets updated when we are processing
CIL checkpoint callbacks. And those callbacks run under AIL lock
contexts, not icloglock context. The CIL checkpoint already knows
what the LSN of the iclog the commit record was written to (obtained
when written into the iclog before submission) and so we can update
the l_last_sync_lsn under the AIL lock in this callback. No other
iclog callbacks will run until the currently executing one
completes, and hence we can update the l_last_sync_lsn under the AIL
lock safely.
This means l_last_sync_lsn can move to the AIL as the "ail_head_lsn"
and it can be used to replace the atomic l_last_sync_lsn in the
iclog code. This makes tracking the log tail belong entirely to the
AIL, rather than being smeared across log, iclog and AIL state and
locking.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
Whenever we write an iclog, we call xlog_assign_tail_lsn() to update
the current tail before we write it into the iclog header. This
means we have to take the AIL lock on every iclog write just to
check if the tail of the log has moved.
This doesn't avoid races with log tail updates - the log tail could
move immediately after we assign the tail to the iclog header and
hence by the time the iclog reaches stable storage the tail LSN has
moved forward in memory. Hence the log tail LSN in the iclog header
is really just a point in time snapshot of the current state of the
AIL.
With this in mind, if we simply update the in memory log->l_tail_lsn
every time it changes in the AIL, there is no need to update the in
memory value when we are writing it into an iclog - it will already
be up-to-date in memory and checking the AIL again will not change
this. Hence xlog_state_release_iclog() does not need to check the
AIL to update the tail lsn and can just sample it directly without
needing to take the AIL lock.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
Currently the AIL attempts to keep 25% of the "log space" free,
where the current used space is tracked by the reserve grant head.
That is, it tracks both physical space used plus the amount reserved
by transactions in progress.
When we start tail pushing, we are trying to make space for new
reservations by writing back older metadata and the log is generally
physically full of dirty metadata, and reservations for modifications
in flight take up whatever space the AIL can physically free up.
Hence we don't really need to take into account the reservation
space that has been used - we just need to keep the log tail moving
as fast as we can to free up space for more reservations to be made.
We know exactly how much physical space the journal is consuming in
the AIL (i.e. max LSN - min LSN) so we can base push thresholds
directly on this state rather than have to look at grant head
reservations to determine how much to physically push out of the
log.
This also allows code that needs to know if log items in the current
transaction need to be pushed or re-logged to simply sample the
current target - they don't need to calculate the current target
themselves. This avoids the need for any locking when doing such
checks.
Further, moving to a physical target means we don't need "push all
until empty semantics" like were introduced in the previous patch.
We can now test and clear the "push all" as a one-shot command to
set the target to the current head of the AIL. This allows the
xfsaild to maximise the use of log space right up to the point where
conditions indicate that the xfsaild is not keeping up with load and
it needs to work harder, and as soon as those constraints go away
(i.e. external code no longer needs everything pushed) the xfsaild
will return to maintaining the normal 25% free space thresholds.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
We have a mechanism that checks the amount of log space remaining
available every time we make a transaction reservation. If the
amount of space is below a threshold (25% free) we push on the AIL
to tell it to do more work. To do this, we end up calculating the
LSN that the AIL needs to push to on every reservation and updating
the push target for the AIL with that new target LSN.
This is silly and expensive. The AIL is perfectly capable of
calculating the push target itself, and it will always be running
when the AIL contains objects.
What the target does is determine if the AIL needs to do
any work before it goes back to sleep. If we haven't run out of
reservation space or memory (or some other push all trigger), it
will simply go back to sleep for a while if there is more than 25%
of the journal space free without doing anything.
If there are items in the AIL at a lower LSN than the target, it
will try to push up to the target or to the point of getting stuck
before going back to sleep and trying again soon after.`
Hence we can modify the AIL to calculate it's own 25% push target
before it starts a push using the same reserve grant head based
calculation as is currently used, and remove all the places where we
ask the AIL to push to a new 25% free target. We can also drop the
minimum free space size of 256BBs from the calculation because the
25% of a minimum sized log is *always going to be larger than
256BBs.
This does still require a manual push in certain circumstances.
These circumstances arise when the AIL is not full, but the
reservation grants consume the entire of the free space in the log.
In this case, we still need to push on the AIL to free up space, so
when we hit this condition (i.e. reservation going to sleep to wait
on log space) we do a single push to tell the AIL it should empty
itself. This will keep the AIL moving as new reservations come in
and want more space, rather than keep queuing them and having to
push the AIL repeatedly.
The reason for using the "push all" when grant space runs out is
that we can run out of grant space when there is more than 25% of
the log free. Small logs are notorious for this, and we have a hack
in the log callback code (xlog_state_set_callback()) where we push
the AIL because the *head* moved) to ensure that we kick the AIL
when we consume space in it because that can push us over the "less
than 25% available" available that starts tail pushing back up
again.
Hence when we run out of grant space and are going to sleep, we have
to consider that the grant space may be consuming almost all the log
space and there is almost nothing in the AIL. In this situation, the
AIL pins the tail and moving the tail forwards is the only way the
grant space will come available, so we have to force the AIL to push
everything to guarantee grant space will eventually be returned.
Hence triggering a "push all" just before sleeping removes all the
nasty corner cases we have in other parts of the code that work
around the "we didn't ask the AIL to push enough to free grant
space" condition that leads to log space hangs...
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
The remaining callers of kmem_free() are freeing heap memory, so
we can convert them directly to kfree() and get rid of kmem_free()
altogether.
This conversion was done with:
$ for f in `git grep -l kmem_free fs/xfs`; do
> sed -i s/kmem_free/kfree/ $f
> done
$
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
There's no reason to keep the kmem_zalloc() around anymore, it's
just a thin wrapper around kmalloc(), so lets get rid of it.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
XFS has strict metadata ordering requirements. One of the things it
does is maintain the commit order of items from transaction commit
through the CIL and into the AIL. That is, if a transaction logs
item A before item B in a modification, then they will be inserted
into the CIL in the order {A, B}. These items are then written into
the iclog during checkpointing in the order {A, B}. When the
checkpoint commits, they are supposed to be inserted into the AIL in
the order {A, B}, and when they are pushed from the AIL, they are
pushed in the order {A, B}.
If we crash, log recovery then replays the two items from the
checkpoint in the order {A, B}, resulting in the objects the items
apply to being queued for writeback at the end of the checkpoint
in the order {A, B}. This means recovery behaves the same way as the
runtime code.
In places, we have subtle dependencies on this ordering being
maintained. One of this place is performing intent recovery from the
log. It assumes that recovering an intent will result in a
non-intent object being the first thing that is modified in the
recovery transaction, and so when the transaction commits and the
journal flushes, the first object inserted into the AIL beyond the
intent recovery range will be a non-intent item. It uses the
transistion from intent items to non-intent items to stop the
recovery pass.
A recent log recovery issue indicated that an intent was appearing
as the first item in the AIL beyond the recovery range, hence
breaking the end of recovery detection that exists.
Tracing indicated insertion of the items into the AIL was apparently
occurring in the right order (the intent was last in the commit item
list), but the intent was appearing first in the AIL. IOWs, the
order of items in the AIL was {D,C,B,A}, not {A,B,C,D}, and bulk
insertion was reversing the order of the items in the batch of items
being inserted.
Lucky for us, all the items fed to bulk insertion have the same LSN,
so the reversal of order does not affect the log head/tail tracking
that is based on the contents of the AIL. It only impacts on code
that has implicit, subtle dependencies on object order, and AFAICT
only the intent recovery loop is impacted by it.
Make sure bulk AIL insertion does not reorder items incorrectly.
Fixes: 0e57f6a36f ("xfs: bulk AIL insertion during transaction commit")
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>
-Wuninitialized complains about @target in xfsaild_push being
uninitialized in the case where the waitqueue is active but there is no
last item in the AIL to wait for. I /think/ it should never be the case
that the subsequent xfs_trans_ail_cursor_first returns a log item and
hence we'll never end up at XFS_LSN_CMP, but let's make this explicit.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
The assignment to pointer lip is not really required, the pointer lip
is redundant and can be removed.
Cleans up clang-scan warning:
warning: Although the value stored to 'lip' is used in the enclosing
expression, the value is never actually read from 'lip'
[deadcode.DeadStores]
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Rewrite the core freezer to behave better wrt thawing and be simpler
in general.
By replacing PF_FROZEN with TASK_FROZEN, a special block state, it is
ensured frozen tasks stay frozen until thawed and don't randomly wake
up early, as is currently possible.
As such, it does away with PF_FROZEN and PF_FREEZER_SKIP, freeing up
two PF_flags (yay!).
Specifically; the current scheme works a little like:
freezer_do_not_count();
schedule();
freezer_count();
And either the task is blocked, or it lands in try_to_freezer()
through freezer_count(). Now, when it is blocked, the freezer
considers it frozen and continues.
However, on thawing, once pm_freezing is cleared, freezer_count()
stops working, and any random/spurious wakeup will let a task run
before its time.
That is, thawing tries to thaw things in explicit order; kernel
threads and workqueues before doing bringing SMP back before userspace
etc.. However due to the above mentioned races it is entirely possible
for userspace tasks to thaw (by accident) before SMP is back.
This can be a fatal problem in asymmetric ISA architectures (eg ARMv9)
where the userspace task requires a special CPU to run.
As said; replace this with a special task state TASK_FROZEN and add
the following state transitions:
TASK_FREEZABLE -> TASK_FROZEN
__TASK_STOPPED -> TASK_FROZEN
__TASK_TRACED -> TASK_FROZEN
The new TASK_FREEZABLE can be set on any state part of TASK_NORMAL
(IOW. TASK_INTERRUPTIBLE and TASK_UNINTERRUPTIBLE) -- any such state
is already required to deal with spurious wakeups and the freezer
causes one such when thawing the task (since the original state is
lost).
The special __TASK_{STOPPED,TRACED} states *can* be restored since
their canonical state is in ->jobctl.
With this, frozen tasks need an explicit TASK_FROZEN wakeup and are
free of undue (early / spurious) wakeups.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20220822114649.055452969@infradead.org
We've got a mess on our hands.
1. xfs_trans_commit() cannot cancel transactions because the mount is
shut down - that causes dirty, aborted, unlogged log items to sit
unpinned in memory and potentially get written to disk before the
log is shut down. Hence xfs_trans_commit() can only abort
transactions when xlog_is_shutdown() is true.
2. xfs_force_shutdown() is used in places to cause the current
modification to be aborted via xfs_trans_commit() because it may be
impractical or impossible to cancel the transaction directly, and
hence xfs_trans_commit() must cancel transactions when
xfs_is_shutdown() is true in this situation. But we can't do that
because of #1.
3. Log IO errors cause log shutdowns by calling xfs_force_shutdown()
to shut down the mount and then the log from log IO completion.
4. xfs_force_shutdown() can result in a log force being issued,
which has to wait for log IO completion before it will mark the log
as shut down. If #3 races with some other shutdown trigger that runs
a log force, we rely on xfs_force_shutdown() silently ignoring #3
and avoiding shutting down the log until the failed log force
completes.
5. To ensure #2 always works, we have to ensure that
xfs_force_shutdown() does not return until the the log is shut down.
But in the case of #4, this will result in a deadlock because the
log Io completion will block waiting for a log force to complete
which is blocked waiting for log IO to complete....
So the very first thing we have to do here to untangle this mess is
dissociate log shutdown triggers from mount shutdowns. We already
have xlog_forced_shutdown, which will atomically transistion to the
log a shutdown state. Due to internal asserts it cannot be called
multiple times, but was done simply because the only place that
could call it was xfs_do_force_shutdown() (i.e. the mount shutdown!)
and that could only call it once and once only. So the first thing
we do is remove the asserts.
We then convert all the internal log shutdown triggers to call
xlog_force_shutdown() directly instead of xfs_force_shutdown(). This
allows the log shutdown triggers to shut down the log without
needing to care about mount based shutdown constraints. This means
we shut down the log independently of the mount and the mount may
not notice this until it's next attempt to read or modify metadata.
At that point (e.g. xfs_trans_commit()) it will see that the log is
shutdown, error out and shutdown the mount.
To ensure that all the unmount behaviours and asserts track
correctly as a result of a log shutdown, propagate the shutdown up
to the mount if it is not already set. This keeps the mount and log
state in sync, and saves a huge amount of hassle where code fails
because of a log shutdown but only checks for mount shutdowns and
hence ends up doing the wrong thing. Cleaning up that mess is
an exercise for another day.
This enables us to address the other problems noted above in
followup patches.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
The AIL operates purely on log items, so it is a log centric
subsystem. Divorce it from the xfs_mount and instead have it pass
around xlog pointers.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
