[BUG]
There is a possible use-after-free bug when running generic/095.
BUG: Unable to handle kernel data access on write at 0x6b6b6b6b6b6b725b
Faulting instruction address: 0xc000000000283654
c000000000283078 do_raw_spin_unlock+0x88/0x230
c0000000012b1e14 _raw_spin_unlock_irqrestore+0x44/0x90
c000000000a918dc btrfs_subpage_clear_writeback+0xac/0xe0
c0000000009e0458 end_bio_extent_writepage+0x158/0x270
c000000000b6fd14 bio_endio+0x254/0x270
c0000000009fc0f0 btrfs_end_bio+0x1a0/0x200
c000000000b6fd14 bio_endio+0x254/0x270
c000000000b781fc blk_update_request+0x46c/0x670
c000000000b8b394 blk_mq_end_request+0x34/0x1d0
c000000000d82d1c lo_complete_rq+0x11c/0x140
c000000000b880a4 blk_complete_reqs+0x84/0xb0
c0000000012b2ca4 __do_softirq+0x334/0x680
c0000000001dd878 irq_exit+0x148/0x1d0
c000000000016f4c do_IRQ+0x20c/0x240
c000000000009240 hardware_interrupt_common_virt+0x1b0/0x1c0
[CAUSE]
There is very small race window like the following in generic/095.
Thread 1 | Thread 2
--------------------------------+------------------------------------
end_bio_extent_writepage() | btrfs_releasepage()
|- spin_lock_irqsave() | |
|- end_page_writeback() | |
| | |- if (PageWriteback() ||...)
| | |- clear_page_extent_mapped()
| | |- kfree(subpage);
|- spin_unlock_irqrestore().
The race can also happen between writeback and btrfs_invalidatepage(),
although that would be much harder as btrfs_invalidatepage() has much
more work to do before the clear_page_extent_mapped() call.
[FIX]
Here we "wait" for the subapge spinlock to be released before we detach
subpage structure.
So this patch will introduce a new function, wait_subpage_spinlock(), to
do the "wait" by acquiring the spinlock and release it.
Since the caller has ensured the page is not dirty nor writeback, and
page is already locked, the only way to hold the subpage spinlock is
from endio function.
Thus we only need to acquire the spinlock to wait for any existing
holder.
Reported-by: Ritesh Harjani <riteshh@linux.ibm.com>
Tested-by: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[BUG]
When running fsstress with subpage RW support, there are random
BUG_ON()s triggered with the following trace:
kernel BUG at fs/btrfs/file-item.c:667!
Internal error: Oops - BUG: 0 [#1] SMP
CPU: 1 PID: 3486 Comm: kworker/u13:2 5.11.0-rc4-custom+ #43
Hardware name: Radxa ROCK Pi 4B (DT)
Workqueue: btrfs-worker-high btrfs_work_helper [btrfs]
pstate: 60000005 (nZCv daif -PAN -UAO -TCO BTYPE=--)
pc : btrfs_csum_one_bio+0x420/0x4e0 [btrfs]
lr : btrfs_csum_one_bio+0x400/0x4e0 [btrfs]
Call trace:
btrfs_csum_one_bio+0x420/0x4e0 [btrfs]
btrfs_submit_bio_start+0x20/0x30 [btrfs]
run_one_async_start+0x28/0x44 [btrfs]
btrfs_work_helper+0x128/0x1b4 [btrfs]
process_one_work+0x22c/0x430
worker_thread+0x70/0x3a0
kthread+0x13c/0x140
ret_from_fork+0x10/0x30
[CAUSE]
Above BUG_ON() means there is some bio range which doesn't have ordered
extent, which indeed is worth a BUG_ON().
Unlike regular sectorsize == PAGE_SIZE case, in subpage we have extra
subpage dirty bitmap to record which range is dirty and should be
written back.
This means, if we submit bio for a subpage range, we do not only need to
clear page dirty, but also need to clear subpage dirty bits.
In __extent_writepage_io(), we will call btrfs_page_clear_dirty() for
any range we submit a bio.
But there is loophole, if we hit a range which is beyond i_size, we just
call btrfs_writepage_endio_finish_ordered() to finish the ordered io,
then break out, without clearing the subpage dirty.
This means, if we hit above branch, the subpage dirty bits are still
there, if other range of the page get dirtied and we need to writeback
that page again, we will submit bio for the old range, leaving a wild
bio range which doesn't have ordered extent.
[FIX]
Fix it by always calling btrfs_page_clear_dirty() in
__extent_writepage_io().
Also to avoid such problem from happening again, add a new assert,
btrfs_page_assert_not_dirty(), to make sure both page dirty and subpage
dirty bits are cleared before exiting __extent_writepage_io().
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[BUG]
There is a very rare ASSERT() triggering during full fstests run for
subpage rw support.
No other reproducer so far.
The ASSERT() gets triggered for metadata read in
btrfs_page_set_uptodate() inside end_page_read().
[CAUSE]
There is still a small race window for metadata only, the race could
happen like this:
T1 | T2
------------------------------------+-----------------------------
end_bio_extent_readpage() |
|- btrfs_validate_metadata_buffer() |
| |- free_extent_buffer() |
| Still have 2 refs |
|- end_page_read() |
|- if (unlikely(PagePrivate()) |
| The page still has Private |
| | free_extent_buffer()
| | | Only one ref 1, will be
| | | released
| | |- detach_extent_buffer_page()
| | |- btrfs_detach_subpage()
|- btrfs_set_page_uptodate() |
The page no longer has Private|
>>> ASSERT() triggered <<< |
This race window is super small, thus pretty hard to hit, even with so
many runs of fstests.
But the race window is still there, we have to go another way to solve
it other than relying on random PagePrivate() check.
Data path is not affected, as it will lock the page before reading,
while unlocking the page after the last read has finished, thus no race
window.
[FIX]
This patch will fix the bug by repurposing btrfs_subpage::readers.
Now btrfs_subpage::readers will be a member shared by both metadata and
data.
For metadata path, we don't do the page unlock as metadata only relies
on extent locking.
At the same time, teach page_range_has_eb() to take
btrfs_subpage::readers into consideration.
So that even if the last eb of a page gets freed, page::private won't be
detached as long as there still are pending end_page_read() calls.
By this we eliminate the race window, this will slight increase the
metadata memory usage, as the page may not be released as frequently as
usual. But it should not be a big deal.
The code got introduced in ("btrfs: submit read time repair only for
each corrupted sector"), but the fix is in a separate patch to keep the
problem description and the crash is rare so it should not hurt
bisectability.
Signed-off-by: Qu Wegruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This patch introduces the following functions to handle btrfs subpage
ordered (Private2) status:
- btrfs_subpage_set_ordered()
- btrfs_subpage_clear_ordered()
- btrfs_subpage_test_ordered()
These helpers can only be called when the range is ensured to be
inside the page.
- btrfs_page_set_ordered()
- btrfs_page_clear_ordered()
- btrfs_page_test_ordered()
These helpers can handle both regular sector size and subpage without
problem.
These functions are here to coordinate btrfs_invalidatepage() with
btrfs_writepage_endio_finish_ordered(), to make sure only one of those
functions can finish the ordered extent.
Tested-by: Ritesh Harjani <riteshh@linux.ibm.com> # [ppc64]
Tested-by: Anand Jain <anand.jain@oracle.com> # [aarch64]
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Introduce a new data inodes specific subpage member, writers, to record
how many sectors are under page lock for delalloc writing.
This member acts pretty much the same as readers, except it's only for
delalloc writes.
This is important for delalloc code to trace which page can really be
freed, as we have cases like run_delalloc_nocow() where we may exit
processing nocow range inside a page, but need to exit to do cow half
way.
In that case, we need a way to determine if we can really unlock a full
page.
With the new btrfs_subpage::writers, there is a new requirement:
- Page locked by process_one_page() must be unlocked by
process_one_page()
There are still tons of call sites manually lock and unlock a page,
without updating btrfs_subpage::writers.
So if we lock a page through process_one_page() then it must be
unlocked by process_one_page() to keep btrfs_subpage::writers
consistent.
This will be handled in next patch.
Tested-by: Ritesh Harjani <riteshh@linux.ibm.com> # [ppc64]
Tested-by: Anand Jain <anand.jain@oracle.com> # [aarch64]
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
In the coming subpage RW supports, there are a lot of page status update
calls which need to be converted to subpage compatible version, which
needs @start and @len.
Some call sites already have such @start/@len and are already in
page range, like various endio functions.
But there are also call sites which need to clamp the range for subpage
case, like btrfs_dirty_pagse() and __process_contig_pages().
Here we introduce new helpers, btrfs_page_clamp_*(), to do and only do the
clamp for subpage version.
Although in theory all existing btrfs_page_*() calls can be converted to
use btrfs_page_clamp_*() directly, but that would make us to do
unnecessary clamp operations.
Tested-by: Ritesh Harjani <riteshh@linux.ibm.com> # [ppc64]
Tested-by: Anand Jain <anand.jain@oracle.com> # [aarch64]
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This patch adds an overview how btrfs subpage support works:
- limitations
- behavior
- basic implementation points
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Introduces the following functions to handle subpage writeback status:
- btrfs_subpage_set_writeback()
- btrfs_subpage_clear_writeback()
- btrfs_subpage_test_writeback()
These helpers can only be called when the range is ensured to be
inside the page.
- btrfs_page_set_writeback()
- btrfs_page_clear_writeback()
- btrfs_page_test_writeback()
These helpers can handle both regular sector size and subpage without
problem.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Introduce the following functions to handle subpage dirty status:
- btrfs_subpage_set_dirty()
- btrfs_subpage_clear_dirty()
- btrfs_subpage_test_dirty()
These helpers can only be called when the range is ensured to be
inside the page.
- btrfs_page_set_dirty()
- btrfs_page_clear_dirty()
- btrfs_page_test_dirty()
These helpers can handle both regular sector size and subpage without
problem.
Thus they would be used to replace PageDirty() related calls in
later patches.
There is one special point to note here, just like set_page_dirty() and
clear_page_dirty_for_io(), btrfs_*page_set_dirty() and
btrfs_*page_clear_dirty() must be called with page locked.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
In btrfs data page read path, the page status update are handled in two
different locations:
btrfs_do_read_page()
{
while (cur <= end) {
/* No need to read from disk */
if (HOLE/PREALLOC/INLINE){
memset();
set_extent_uptodate();
continue;
}
/* Read from disk */
ret = submit_extent_page(end_bio_extent_readpage);
}
end_bio_extent_readpage()
{
endio_readpage_uptodate_page_status();
}
This is fine for sectorsize == PAGE_SIZE case, as for above loop we
should only hit one branch and then exit.
But for subpage, there is more work to be done in page status update:
- Page Unlock condition
Unlike regular page size == sectorsize case, we can no longer just
unlock a page.
Only the last reader of the page can unlock the page.
This means, we can unlock the page either in the while() loop, or in
the endio function.
- Page uptodate condition
Since we have multiple sectors to read for a page, we can only mark
the full page uptodate if all sectors are uptodate.
To handle both subpage and regular cases, introduce a pair of functions
to help handling page status update:
- begin_page_read()
For regular case, it does nothing.
For subpage case, it updates the reader counters so that later
end_page_read() can know who is the last one to unlock the page.
- end_page_read()
This is just endio_readpage_uptodate_page_status() renamed.
The original name is a little too long and too specific for endio.
The new thing added is the condition for page unlock.
Now for subpage data, we unlock the page if we're the last reader.
This does not only provide the basis for subpage data read, but also
hide the special handling of page read from the main read loop.
Also, since we're changing how the page lock is handled, there are two
existing error paths where we need to manually unlock the page before
calling begin_page_read().
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Introduce the following functions to handle subpage error status:
- btrfs_subpage_set_error()
- btrfs_subpage_clear_error()
- btrfs_subpage_test_error()
These helpers can only be called when the page has subpage attached
and the range is ensured to be inside the page.
- btrfs_page_set_error()
- btrfs_page_clear_error()
- btrfs_page_test_error()
These helpers can handle both regular sector size and subpage without
problem.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Introduce the following functions to handle subpage uptodate status:
- btrfs_subpage_set_uptodate()
- btrfs_subpage_clear_uptodate()
- btrfs_subpage_test_uptodate()
These helpers can only be called when the page has subpage attached
and the range is ensured to be inside the page.
- btrfs_page_set_uptodate()
- btrfs_page_clear_uptodate()
- btrfs_page_test_uptodate()
These helpers can handle both regular sector size and subpage.
Although caller should still ensure that the range is inside the page.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
In btrfs_release_extent_buffer_pages(), we need to add extra handling
for subpage.
Introduce a helper, detach_extent_buffer_page(), to do different
handling for regular and subpage cases.
For subpage case, handle detaching page private.
For unmapped (dummy or cloned) ebs, we can detach the page private
immediately as the page can only be attached to one unmapped eb.
For mapped ebs, we have to ensure there are no eb in the page range
before we delete it, as page->private is shared between all ebs in the
same page.
But there is a subpage specific race, where we can race with extent
buffer allocation, and clear the page private while new eb is still
being utilized, like this:
Extent buffer A is the new extent buffer which will be allocated,
while extent buffer B is the last existing extent buffer of the page.
T1 (eb A) | T2 (eb B)
-------------------------------+------------------------------
alloc_extent_buffer() | btrfs_release_extent_buffer_pages()
|- p = find_or_create_page() | |
|- attach_extent_buffer_page() | |
| | |- detach_extent_buffer_page()
| | |- if (!page_range_has_eb())
| | | No new eb in the page range yet
| | | As new eb A hasn't yet been
| | | inserted into radix tree.
| | |- btrfs_detach_subpage()
| | |- detach_page_private();
|- radix_tree_insert() |
Then we have a metadata eb whose page has no private bit.
To avoid such race, we introduce a subpage metadata-specific member,
btrfs_subpage::eb_refs.
In alloc_extent_buffer() we increase eb_refs in the critical section of
private_lock. Then page_range_has_eb() will return true for
detach_extent_buffer_page(), and will not detach page private.
The section is marked by:
- btrfs_page_inc_eb_refs()
- btrfs_page_dec_eb_refs()
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
For subpage case, we need to allocate additional memory for each
metadata page.
So we need to:
- Allow attach_extent_buffer_page() to return int to indicate allocation
failure
- Allow manually pre-allocate subpage memory for alloc_extent_buffer()
As we don't want to use GFP_ATOMIC under spinlock, we introduce
btrfs_alloc_subpage() and btrfs_free_subpage() functions for this
purpose.
(The simple wrap for btrfs_free_subpage() is for later convert to
kmem_cache. Already internally tested without problem)
- Preallocate btrfs_subpage structure for alloc_extent_buffer()
We don't want to call memory allocation with spinlock held, so
do preallocation before we acquire mapping->private_lock.
- Handle subpage and regular case differently in
attach_extent_buffer_page()
For regular case, no change, just do the usual thing.
For subpage case, allocate new memory or use the preallocated memory.
For future subpage metadata, we will make use of radix tree to grab
extent buffer.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
For sectorsize < page size support, we need a structure to record extra
status info for each sector of a page.
Introduce the skeleton structure, all subpage related code would go to
subpage.[ch].
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
