fstrim will hold the AGF lock for as long as it takes to walk and
discard all the free space in the AG that meets the userspace trim
criteria. For AGs with lots of free space extents (e.g. millions)
or the underlying device is really slow at processing discard
requests (e.g. Ceph RBD), this means the AGF hold time is often
measured in minutes to hours, not a few milliseconds as we normal
see with non-discard based operations.
This can result in the entire filesystem hanging whilst the
long-running fstrim is in progress. We can have transactions get
stuck waiting for the AGF lock (data or metadata extent allocation
and freeing), and then more transactions get stuck waiting on the
locks those transactions hold. We can get to the point where fstrim
blocks an extent allocation or free operation long enough that it
ends up pinning the tail of the log and the log then runs out of
space. At this point, every modification in the filesystem gets
blocked. This includes read operations, if atime updates need to be
made.
To fix this problem, we need to be able to discard free space
extents safely without holding the AGF lock. Fortunately, we already
do this with online discard via busy extents. We can mark free space
extents as "busy being discarded" under the AGF lock and then unlock
the AGF, knowing that nobody will be able to allocate that free
space extent until we remove it from the busy tree.
Modify xfs_trim_extents to use the same asynchronous discard
mechanism backed by busy extents as is used with online discard.
This results in the AGF only needing to be held for short periods of
time and it is never held while we issue discards. Hence if discard
submission gets throttled because it is slow and/or there are lots
of them, we aren't preventing other operations from being performed
on AGF while we wait for discards to complete...
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Because we are going to use the same list-based discard submission
interface for fstrim-based discards, too.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
If the current transaction holds a busy extent and we are trying to
allocate a new extent to fix up the free list, we can deadlock if
the AG is entirely empty except for the busy extent held by the
transaction.
This can occur at runtime processing an XEFI with multiple extents
in this path:
__schedule+0x22f at ffffffff81f75e8f
schedule+0x46 at ffffffff81f76366
xfs_extent_busy_flush+0x69 at ffffffff81477d99
xfs_alloc_ag_vextent_size+0x16a at ffffffff8141711a
xfs_alloc_ag_vextent+0x19b at ffffffff81417edb
xfs_alloc_fix_freelist+0x22f at ffffffff8141896f
xfs_free_extent_fix_freelist+0x6a at ffffffff8141939a
__xfs_free_extent+0x99 at ffffffff81419499
xfs_trans_free_extent+0x3e at ffffffff814a6fee
xfs_extent_free_finish_item+0x24 at ffffffff814a70d4
xfs_defer_finish_noroll+0x1f7 at ffffffff81441407
xfs_defer_finish+0x11 at ffffffff814417e1
xfs_itruncate_extents_flags+0x13d at ffffffff8148b7dd
xfs_inactive_truncate+0xb9 at ffffffff8148bb89
xfs_inactive+0x227 at ffffffff8148c4f7
xfs_fs_destroy_inode+0xb8 at ffffffff81496898
destroy_inode+0x3b at ffffffff8127d2ab
do_unlinkat+0x1d1 at ffffffff81270df1
do_syscall_64+0x40 at ffffffff81f6b5f0
entry_SYSCALL_64_after_hwframe+0x44 at ffffffff8200007c
This can also happen in log recovery when processing an EFI
with multiple extents through this path:
context_switch() kernel/sched/core.c:3881
__schedule() kernel/sched/core.c:5111
schedule() kernel/sched/core.c:5186
xfs_extent_busy_flush() fs/xfs/xfs_extent_busy.c:598
xfs_alloc_ag_vextent_size() fs/xfs/libxfs/xfs_alloc.c:1641
xfs_alloc_ag_vextent() fs/xfs/libxfs/xfs_alloc.c:828
xfs_alloc_fix_freelist() fs/xfs/libxfs/xfs_alloc.c:2362
xfs_free_extent_fix_freelist() fs/xfs/libxfs/xfs_alloc.c:3029
__xfs_free_extent() fs/xfs/libxfs/xfs_alloc.c:3067
xfs_trans_free_extent() fs/xfs/xfs_extfree_item.c:370
xfs_efi_recover() fs/xfs/xfs_extfree_item.c:626
xlog_recover_process_efi() fs/xfs/xfs_log_recover.c:4605
xlog_recover_process_intents() fs/xfs/xfs_log_recover.c:4893
xlog_recover_finish() fs/xfs/xfs_log_recover.c:5824
xfs_log_mount_finish() fs/xfs/xfs_log.c:764
xfs_mountfs() fs/xfs/xfs_mount.c:978
xfs_fs_fill_super() fs/xfs/xfs_super.c:1908
mount_bdev() fs/super.c:1417
xfs_fs_mount() fs/xfs/xfs_super.c:1985
legacy_get_tree() fs/fs_context.c:647
vfs_get_tree() fs/super.c:1547
do_new_mount() fs/namespace.c:2843
do_mount() fs/namespace.c:3163
ksys_mount() fs/namespace.c:3372
__do_sys_mount() fs/namespace.c:3386
__se_sys_mount() fs/namespace.c:3383
__x64_sys_mount() fs/namespace.c:3383
do_syscall_64() arch/x86/entry/common.c:296
entry_SYSCALL_64() arch/x86/entry/entry_64.S:180
To avoid this deadlock, we should not block in
xfs_extent_busy_flush() if we hold a busy extent in the current
transaction.
Now that the EFI processing code can handle requeuing a partially
completed EFI, we can detect this situation in
xfs_extent_busy_flush() and return -EAGAIN rather than going to
sleep forever. The -EAGAIN get propagated back out to the
xfs_trans_free_extent() context, where the EFD is populated and the
transaction is rolled, thereby moving the busy extents into the CIL.
At this point, we can retry the extent free operation again with a
clean transaction. If we hit the same "all free extents are busy"
situation when trying to fix up the free list, we can safely call
xfs_extent_busy_flush() and wait for the busy extents to resolve
and wake us. At this point, the allocation search can make progress
again and we can fix up the free list.
This deadlock was first reported by Chandan in mid-2021, but I
couldn't make myself understood during review, and didn't have time
to fix it myself.
It was reported again in March 2023, and again I have found myself
unable to explain the complexities of the solution needed during
review.
As such, I don't have hours more time to waste trying to get the
fix written the way it needs to be written, so I'm just doing it
myself. This patchset is largely based on Wengang Wang's last patch,
but with all the unnecessary stuff removed, split up into multiple
patches and cleaned up somewhat.
Reported-by: Chandan Babu R <chandanrlinux@gmail.com>
Reported-by: Wengang Wang <wen.gang.wang@oracle.com>
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>
To avoid blocking in xfs_extent_busy_flush() when freeing extents
and the only busy extents are held by the current transaction, we
need to pass the XFS_ALLOC_FLAG_FREEING flag context all the way
into xfs_extent_busy_flush().
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>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>
All of the callers of the busy extent API either have perag
references available to use so we can pass a perag to the busy
extent functions rather than having them have to do unnecessary
lookups.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
list_sort() internally casts the comparison function passed to it
to a different type with constant struct list_head pointers, and
uses this pointer to call the functions, which trips indirect call
Control-Flow Integrity (CFI) checking.
Instead of removing the consts, this change defines the
list_cmp_func_t type and changes the comparison function types of
all list_sort() callers to use const pointers, thus avoiding type
mismatches.
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-10-samitolvanen@google.com
Remove the verbose license text from XFS files and replace them
with SPDX tags. This does not change the license of any of the code,
merely refers to the common, up-to-date license files in LICENSES/
This change was mostly scripted. fs/xfs/Makefile and
fs/xfs/libxfs/xfs_fs.h were modified by hand, the rest were detected
and modified by the following command:
for f in `git grep -l "GNU General" fs/xfs/` ; do
echo $f
cat $f | awk -f hdr.awk > $f.new
mv -f $f.new $f
done
And the hdr.awk script that did the modification (including
detecting the difference between GPL-2.0 and GPL-2.0+ licenses)
is as follows:
$ cat hdr.awk
BEGIN {
hdr = 1.0
tag = "GPL-2.0"
str = ""
}
/^ \* This program is free software/ {
hdr = 2.0;
next
}
/any later version./ {
tag = "GPL-2.0+"
next
}
/^ \*\// {
if (hdr > 0.0) {
print "// SPDX-License-Identifier: " tag
print str
print $0
str=""
hdr = 0.0
next
}
print $0
next
}
/^ \* / {
if (hdr > 1.0)
next
if (hdr > 0.0) {
if (str != "")
str = str "\n"
str = str $0
next
}
print $0
next
}
/^ \*/ {
if (hdr > 0.0)
next
print $0
next
}
// {
if (hdr > 0.0) {
if (str != "")
str = str "\n"
str = str $0
next
}
print $0
}
END { }
$
Signed-off-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>
Currently we force the log and simply try again if we hit a busy extent,
but especially with online discard enabled it might take a while after
the log force for the busy extents to disappear, and we might have
already completed our second pass.
So instead we add a new waitqueue and a generation counter to the pag
structure so that we can do wakeups once we've removed busy extents,
and we replace the single retry with an unconditional one - after
all we hold the AGF buffer lock, so no other allocations or frees
can be racing with us in this AG.
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>
Currently the xfs_inode.h header has a dependency on the definition
of the BMAP btree records as the inode fork includes an array of
xfs_bmbt_rec_host_t objects in it's definition.
Move all the btree format definitions from xfs_btree.h,
xfs_bmap_btree.h, xfs_alloc_btree.h and xfs_ialloc_btree.h to
xfs_format.h to continue the process of centralising the on-disk
format definitions. With this done, the xfs inode definitions are no
longer dependent on btree header files.
The enables a massive culling of unnecessary includes, with close to
200 #include directives removed from the XFS kernel code base.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Commit e459df5, 'xfs: move busy extent handling to it's own file'
moved some code from xfs_alloc.c into xfs_extent_busy.c for
convenience in userspace code merges. One of the functions moved is
xfs_extent_busy_trim (formerly xfs_alloc_busy_trim) which is defined
STATIC. Unfortunately this function is still used in xfs_alloc.c, and
this results in an undefined symbol in xfs.ko.
Make xfs_extent_busy_trim not static and add its prototype to
xfs_extent_busy.h.
Signed-off-by: Ben Myers <bpm@sgi.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Now that the busy extent tracking has been moved out of the
allocation files, clean up the namespace it uses to
"xfs_extent_busy" rather than a mix of "xfs_busy" and
"xfs_alloc_busy".
Signed-off-by: Dave Chinner<dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
To make it easier to handle userspace code merges, move all the busy
extent handling out of the allocation code and into it's own file.
The userspace code does not need the busy extent code, so this
simplifies the merging of the kernel code into the userspace
xfsprogs library.
Because the busy extent code has been almost completely rewritten
over the past couple of years, also update the copyright on this new
file to include the authors that made all those changes.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
