Re: current->journal_info got nested! (was Re: [syzbot] [xfs?] [ext4?] general protection fault in jbd2__journal_start)

[Christoph Hellwig]

On Wed, Jan 31, 2024 at 05:20:10AM +0000, Matthew Wilcox wrote:
> I'd suggest that saving off current->journal_info is risky because
> it might cover a real problem where you've taken a pagefault inside
> a transaction (eg ext4 faulting while in the middle of a transaction on
> the same filesystem that contains the faulting file).

Agreed.

> Seems to me that we shouldn't be writing to userspace while in the
> middle of a transaction.  We could even assert that in copy_to_user()?

That sounds useful, but also rather expensive.