Re: [f2fs-dev] [PATCH] f2fs: fix to zero post-EOF data when extending file size

From: Chao Yu

Date: Wed Jul 29 2026 - 04:33:26 EST

On 7/29/26 11:41, Jaegeuk Kim wrote:
> On 07/20, Chao Yu via Linux-f2fs-devel wrote:
>> On 7/16/26 02:05, Jaegeuk Kim wrote:
>>> This causes sysmtem hang during xfstests.
>>
>> Fixed a potential deadlock issue during checkpoint in v2, though I can
>> not reproduce it.
>
> I got this on generic/269 with v2. I'll dequeue the patch first.

Oh, sorry, will take a look.

To confirm, do you run generic/269 test w/ fsync_mode=strict mount option?

If so, I guess this patch will run out-of-space since we trigger page writeback
of regular inodes during checkpoint(). :/

Thanks,

>
> [ 90.879237] ------------[ cut here ]------------
> [ 90.881987] kernel BUG at segment.c:2902!
> [ 90.884058] Oops: invalid opcode: 0000 [#1] SMP NOPTI
> [ 90.886628] CPU: 7 UID: 0 PID: 2566 Comm: f2fs_ckpt-252:3 Tainted: G OE 7.2.0-rc5-custom #1 PREEMPT(full)
> [ 90.891533] Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
> [ 90.894647] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
> [ 90.900014] RIP: 0010:new_curseg+0xa17/0xa60 [f2fs]
> [ 90.902240] Code: 8b 71 48 e9 16 f8 ff ff 4c 8b 69 08 41 8b 84 24 4c 06 00 00 31 d2 41 8b 8c 24 48 06 00 00 f7 f1 89 45 a4 89 f0 e9 e9 fe ff ff <0f> 0b 49 8b 3c 24 68 40 0c 00 00 45 31 c0 31 c9 41 b9 8b ff ff ff
> [ 90.910818] RSP: 0018:ffffd4acc4167670 EFLAGS: 00010293
> [ 90.913153] RAX: 00000000000000f8 RBX: 0000000000000000 RCX: 0000000000000000
> [ 90.916400] RDX: ffffffffffffffff RSI: 00000000000000f8 RDI: 00000000000000f8
> [ 90.919494] RBP: ffffd4acc41676d0 R08: ffff8d640bdab2a0 R09: ffffffffc10673eb
> [ 90.923182] R10: 00000000000000f8 R11: 0000000000000014 R12: ffff8d64892c6000
> [ 90.926315] R13: ffff8d648c236b80 R14: 00000000000000f8 R15: 0000000000000000
> [ 90.929430] FS: 0000000000000000(0000) GS:ffff8d6504b73000(0000) knlGS:0000000000000000
> [ 90.933668] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 90.937206] CR2: 00005577fade9868 CR3: 0000000092d82002 CR4: 0000000000372ef0
> [ 90.940305] Call Trace:
> [ 90.941486] <TASK>
> [ 90.942464] f2fs_allocate_data_block+0x69b/0xb10 [f2fs]
> [ 90.944862] do_write_page+0x72/0x360 [f2fs]
> [ 90.946798] ? __folio_start_writeback+0x90/0x1d0
> [ 90.949485] f2fs_do_write_node_page+0x35/0x70 [f2fs]
> [ 90.952813] __write_node_folio+0x33c/0x640 [f2fs]
> [ 90.955104] ? debug_smp_processor_id+0x17/0x20
> [ 90.957550] f2fs_sync_node_pages+0x3d8/0x530 [f2fs]
> [ 90.960954] block_operations+0x41d/0x590 [f2fs]
> [ 90.963415] ? __pfx_issue_checkpoint_thread+0x10/0x10 [f2fs]
> [ 90.966293] f2fs_write_checkpoint+0x15a/0x13c0 [f2fs]
> [ 90.969193] ? update_load_avg+0x79/0x2e0
> [ 90.971712] ? kvm_clock_get_cycles+0x18/0x40
> [ 90.974030] ? module_sect_read+0x81/0xc0
> [ 90.976675] ? __pfx_issue_checkpoint_thread+0x10/0x10 [f2fs]
> [ 90.980146] __write_checkpoint_sync+0x75/0xb0 [f2fs]
> [ 90.983100] __checkpoint_and_complete_reqs+0x3b/0x110 [f2fs]
> [ 90.986332] ? __pfx_issue_checkpoint_thread+0x10/0x10 [f2fs]
> [ 90.989853] issue_checkpoint_thread+0x4b/0x100 [f2fs]
> [ 90.992622] ? __pfx_autoremove_wake_function+0x10/0x10
> [ 90.995875] kthread+0x10a/0x140
> [ 90.998141] ? __pfx_kthread+0x10/0x10
> [ 91.000585] ret_from_fork+0x1ef/0x2b0
> [ 91.002565] ? __pfx_kthread+0x10/0x10
> [ 91.004510] ret_from_fork_asm+0x1a/0x30
>
>>
>> Thanks,
>>
>>>
>>> On 07/06, Chao Yu via Linux-f2fs-devel wrote:
>>>> generic/794 4s ... - output mismatch (see /share/git/fstests/results//generic/794.out.bad)
>>>> --- tests/generic/794.out 2026-06-12 08:46:32.766426241 +0800
>>>> +++ /share/git/fstests/results//generic/794.out.bad 2026-07-05 18:32:55.000000000 +0800
>>>> @@ -1,4 +1,16 @@
>>>> QA output created by 794
>>>> append_write
>>>> +FAIL: non-zero data in gap [4080,4096) after shutdown+remount
>>>> +000000 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >ZZZZZZZZZZZZZZZZ<
>>>> +*
>>>> +001000
>>>> truncate_up
>>>> ...
>>>> (Run 'diff -u /share/git/fstests/tests/generic/794.out /share/git/fstests/results//generic/794.out.bad' to see the entire diff)
>>>> Ran: generic/794
>>>> Failures: generic/794
>>>> Failed 1 of 1 tests
>>>>
>>>> Steps of generic/794:
>>>> 1. write 4096 bytes to file w/ 0x5a
>>>> 2. use fiemap to get PBA of first block in file
>>>> 3. truncate file to 4080
>>>> 4. umount; write 4096 bytes to file w/ 0x5a directly via PBA; mount
>>>> 5. extend filesize via
>>>> a) append 4096 from offset 4096, or
>>>> b) truncate 8192, or
>>>> c) fallocate 4096 from offset 4096
>>>> 6. verify the gap is zeroed in memory [4080,4096)
>>>> 7. sync range 4096 from offset 4096; shutdown -f (flush meta before shutdown)
>>>> 8. umount; mount; verify [4080,4096) is zeroed or not.
>>>>
>>>> When extending file size (e.g. via truncate, fallocate, or write) across an
>>>> unaligned EOF boundary, we need to ensure that post-EOF data in the partial
>>>> page is zeroed out in pagecache and marked dirty, meanwhile, tagging the inode
>>>> with FI_ZERO_POST_EOF, so that following checkpoint() and fsync() can persist
>>>> the page contain zeroed data before committing inode w/ updated i_size.
>>>>
>>>> This help to prevent stale disk data beyond the previous EOF from being exposed
>>>> after remounting or crash recovery.
>>>>
>>>> Since f2fs is a LFS filesystem, we only support direct write via PBA in pinfile,
>>>> and pinfile has section-aligned filesize, so in Android, there should no problem,
>>>> but for other usage in different environment, let's fix this w/ fsync_mode=strict
>>>> mount option.
>>>>
>>>> Cc: stable@xxxxxxxxxx
>>>> Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
>>>> ---
>>>> fs/f2fs/checkpoint.c | 4 ++++
>>>> fs/f2fs/f2fs.h | 1 +
>>>> fs/f2fs/file.c | 35 ++++++++++++++++++++++++++++++++---
>>>> 3 files changed, 37 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>>> index 064f5b537423..6f486d3a94c7 100644
>>>> --- a/fs/f2fs/checkpoint.c
>>>> +++ b/fs/f2fs/checkpoint.c
>>>> @@ -1359,6 +1359,10 @@ static int f2fs_sync_inode_meta(struct f2fs_sb_info *sbi)
>>>> inode = igrab(&fi->vfs_inode);
>>>> spin_unlock(&sbi->inode_lock[DIRTY_META]);
>>>> if (inode) {
>>>> + if (is_inode_flag_set(inode, FI_ZERO_POST_EOF)) {
>>>> + filemap_write_and_wait(inode->i_mapping);
>>>> + clear_inode_flag(inode, FI_ZERO_POST_EOF);
>>>> + }
>>>> sync_inode_metadata(inode, 0);
>>>> /* it's on eviction */
>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>> index 8e2fb0bda467..41be09dad43c 100644
>>>> --- a/fs/f2fs/f2fs.h
>>>> +++ b/fs/f2fs/f2fs.h
>>>> @@ -939,6 +939,7 @@ enum {
>>>> FI_ATOMIC_REPLACE, /* indicate atomic replace */
>>>> FI_OPENED_FILE, /* indicate file has been opened */
>>>> FI_DONATE_FINISHED, /* indicate page donation of file has been finished */
>>>> + FI_ZERO_POST_EOF, /* indicate unaligned EOF gap was zeroed in pagecache */
>>>> FI_MAX, /* max flag, never be used */
>>>> };
>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>> index 11cc8d79c235..2e9d585073ec 100644
>>>> --- a/fs/f2fs/file.c
>>>> +++ b/fs/f2fs/file.c
>>>> @@ -36,21 +36,43 @@
>>>> #include <trace/events/f2fs.h>
>>>> #include <uapi/linux/f2fs.h>
>>>> +static int fill_zero(struct inode *inode, pgoff_t index,
>>>> + loff_t start, loff_t len);
>>>> +
>>>> static void f2fs_zero_post_eof_page(struct inode *inode,
>>>> loff_t new_size, bool lock)
>>>> {
>>>> loff_t old_size = i_size_read(inode);
>>>> + unsigned int offset;
>>>> if (old_size >= new_size)
>>>> return;
>>>> - if (mapping_empty(inode->i_mapping))
>>>> - return;
>>>> -
>>>> if (lock)
>>>> filemap_invalidate_lock(inode->i_mapping);
>>>> +
>>>> /* zero or drop pages only in range of [old_size, new_size] */
>>>> truncate_inode_pages_range(inode->i_mapping, old_size, new_size);
>>>> +
>>>> + /*
>>>> + * When expanding an unaligned EOF size, zero post-EOF data in
>>>> + * pagecache and set FI_ZERO_POST_EOF, so following checkpointing
>>>> + * or fsync can persist correct data to disk before committing
>>>> + * inode w/ updated i_size.
>>>> + */
>>>> + if (F2FS_OPTION(F2FS_I_SB(inode)).fsync_mode != FSYNC_MODE_STRICT)
>>>> + goto out_unlock;
>>>> +
>>>> + offset = old_size & (PAGE_SIZE - 1);
>>>> + if (offset) {
>>>> + unsigned int len = min_t(loff_t, PAGE_SIZE - offset,
>>>> + new_size - old_size);
>>>> + pgoff_t index = old_size >> PAGE_SHIFT;
>>>> +
>>>> + fill_zero(inode, index, offset, len);
>>>> + set_inode_flag(inode, FI_ZERO_POST_EOF);
>>>> + }
>>>> +out_unlock:
>>>> if (lock)
>>>> filemap_invalidate_unlock(inode->i_mapping);
>>>> }
>>>> @@ -304,6 +326,13 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end,
>>>> if (S_ISDIR(inode->i_mode))
>>>> goto go_write;
>>>> + if (is_inode_flag_set(inode, FI_ZERO_POST_EOF)) {
>>>> + ret = filemap_write_and_wait(inode->i_mapping);
>>>> + if (ret)
>>>> + return ret;
>>>> + clear_inode_flag(inode, FI_ZERO_POST_EOF);
>>>> + }
>>>> +
>>>> /* if fdatasync is triggered, let's do in-place-update */
>>>> if (datasync || get_dirty_pages(inode) <= SM_I(sbi)->min_fsync_blocks)
>>>> set_inode_flag(inode, FI_NEED_IPU);
>>>> --
>>>> 2.49.0
>>>>
>>>>
>>>>
>>>> _______________________________________________
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>>>> Linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>
>>
>>
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