[PATCH 4/4] ubifs: Convert do_writepage() to take a folio

[Richard Weinberger]

Matthew,

----- Ursprüngliche Mail -----
> Von: "Matthew Wilcox" <willy at infradead.org>
> len is folio_size(), which is not 0.
> 
>        len = offset_in_folio(folio, i_size);

offset_in_folio(folio, i_size) can give 0.

Further it will call do_writepage() with len being 0.
I can actually trigger this case.

By adding the following ubifs_assert() I can catch the write side.
If the file length is a multiple of PAGE_SIZE (4k), it will trigger.

diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 67cf5138ccc48..dc39ea368ca2b 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -1059,6 +1059,8 @@ static int ubifs_writepage(struct folio *folio, struct writeback_control *wbc,
        folio_zero_segment(folio, offset_in_folio(folio, i_size), len);
        len = offset_in_folio(folio, i_size);
 
+       ubifs_assert(c, len > 0);
+
        if (i_size > synced_i_size) {
                err = inode->i_sb->s_op->write_inode(inode, NULL);
                if (err)

[   44.569110] UBIFS error (ubi0:0 pid 59): ubifs_assert_failed: UBIFS assert failed: len > 0, in fs/ubifs/file.c:1062
[   44.571359] UBIFS warning (ubi0:0 pid 59): ubifs_ro_mode.part.6: switched to read-only mode, error -22
[   44.572998] CPU: 1 PID: 59 Comm: kworker/u8:2 Not tainted 6.4.0-rc5-00004-gd504b815b71c-dirty #19
[   44.574139] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b-rebuilt.opensuse.org 04/01/2014
[   44.574141] Workqueue: writeback wb_workfn (flush-ubifs_0_0)
[   44.574148] Call Trace:
[   44.574162]  <TASK>
[   44.574165]  dump_stack_lvl+0x32/0x50
[   44.574172]  ubifs_writepage+0x25a/0x270
[   44.578096]  write_cache_pages+0x132/0x3a0
[   44.578103]  ? __pfx_ubifs_writepage+0x10/0x10
[   44.578107]  ? virtqueue_add_sgs+0x7b/0x90
[   44.578113]  do_writepages+0xd3/0x1a0
[   44.578116]  ? kvm_clock_read+0x14/0x30
[   44.578121]  ? kvm_sched_clock_read+0x5/0x20
[   44.578125]  __writeback_single_inode+0x3c/0x350
[   44.578128]  writeback_sb_inodes+0x1c9/0x460
[   44.578133]  __writeback_inodes_wb+0x5a/0xc0
[   44.582508]  wb_writeback+0x230/0x2c0
[   44.582513]  wb_workfn+0x301/0x430
[   44.582515]  ? kvm_clock_read+0x14/0x30
[   44.582519]  ? kvm_sched_clock_read+0x5/0x20
[   44.582523]  ? sched_clock_cpu+0xd/0x190
[   44.582527]  ? __smp_call_single_queue+0xa1/0x110
[   44.582532]  process_one_work+0x1f3/0x3f0
[   44.582538]  worker_thread+0x25/0x3b0
[   44.586196]  ? __pfx_worker_thread+0x10/0x10
[   44.586201]  kthread+0xde/0x110
[   44.586204]  ? __pfx_kthread+0x10/0x10
[   44.586207]  ret_from_fork+0x2c/0x50
[   44.586212]  </TASK>

Thanks,
//richard