Re: [PATCH] coredump/fcntl: Add FD_CLOBCOR flag to close fd before dumping core

[Christian Brauner]

On Thu, Jun 18, 2026 at 11:07:00AM +0800, Xin Zhao wrote:
> A coredump typically takes some time to complete. If we happen to hold a
> write lock with flock just before triggering the coredump, that write lock
> will not be released during the entire coredump process. As a result,
> other processes attempting to acquire the same write lock may experience
> significant delays.
> 
> To address this, we introduce the F_[GET|SET]FD_EX fcntl operation and the
> FD_CLOBCOR flag, allowing coredump_wait() to release any file descriptors
> marked with FD_CLOBCOR. We can also assign the FD_CLOBCOR flag to specific
> shared memory segments, preventing the coredump from including shared
> memory that we are not interested in, thereby reducing both the coredump
> duration and the size of the core file.
> 
> We actually considered using signals that generate coredumps to perform
> the actions we wanted in user space. However, since other threads within
> the process are not frozen when handling these signals, indiscriminately
> closing an fd can lead to concurrency issues. For example, if the thread
> that triggered the coredump closes the fd in the signal handler while
> other threads are using the resources associated with that fd, it could
> cause secondary corruption of the coredump state.
> 
> Signed-off-by: Xin Zhao <jackzxcui1989@xxxxxxx>
> ---

Eew, NAK. No way we're doing this.
I can see a point in filtering memory that one isn't interested in but
that has to be built on top of the coredump socket protoctol by
extending it.