How to debug stuck read?

[Dāvis Mosāns]

trešd., 2022. g. 2. febr., plkst. 21:13 — lietotājs Matthew Wilcox
(<willy at infradead.org>) rakstīja:
>
> On Wed, Feb 02, 2022 at 07:15:14PM +0200, Dāvis Mosāns wrote:
> > I have a corrupted file on BTRFS which has CoW disabled thus no
> > checksum. Trying to read this file causes the process to get stuck
> > forever. It doesn't return EIO.
> >
> > How can I find out why it gets stuck?
>
> > $ cat /proc/3449/stack | ./scripts/decode_stacktrace.sh vmlinux
> > folio_wait_bit_common (mm/filemap.c:1314)
> > filemap_get_pages (mm/filemap.c:2622)
> > filemap_read (mm/filemap.c:2676)
> > new_sync_read (fs/read_write.c:401 (discriminator 1))
>
> folio_wait_bit_common() is where it waits for the page to be unlocked.
> Probably the problem is that btrfs isn't unlocking the page on
> seeing the error, so you don't get the -EIO returned?


Yeah, but how to find where that happens.
Anyway by pure luck I found memcpy that wrote outside of allocated
memory and fixing that solved this issue but I still don't know how to
debug this properly.