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Message-ID: <a99a7fbe-ec31-4e31-87c7-1b7ae1dd1a5a@kernel.dk>
Date:   Fri, 27 Oct 2023 09:14:53 -0600
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To:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>
Cc:     LKML <linux-kernel@vger.kernel.org>
From:   Jens Axboe <axboe@kernel.dk>
Subject: lockdep: holding locks across syscall boundaries
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Hi,

Normally we'd expect locking state to be clean and consistent across
syscall entry and exit, as that is always the case for sync syscalls.
We currently have a work-around for holding a lock from aio, see
kiocb_start_write(), which pretends to drop the lock from lockdeps
perspective, as it's held from submission to until kiocb_end_write() is
called at completion time.

This is a bit of an ugly work-around, and defeats the purpose of
lockdep.

Since I've now got another case where I want to hold a resource across
syscalls, is there a better way to do this?

This is for inode_dio_start(), which increments an inode int count, and
inode_dio_end() which decrements it. If a task is doing
inode_dio_start() and then inode_dio_wait(), I want to trigger this. I
have a hack that does this, but it disables lockdep_sys_exit() as
otherwise I just get that warning rather than the more useful one.

Thanks,
-- 
Jens Axboe