I'm the creator and the maintainer of the mold linker (https://github.com/rui314/mold). Recently, we discovered that mold started causing process crashes in certain situations due to a change in the Linux kernel. Here are the details:
- In general, overwriting an existing file is much faster than creating an empty file and writing to it on Linux, so mold attempts to reuse an existing executable file if it exists.
- If a program is running, opening the executable file for writing previously failed with ETXTBSY. If that happens, mold falls back to creating a new file.
- However, the Linux kernel recently changed the behavior so that writing to an executable file is now always permitted (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...). That caused mold to write to an executable file even if there's a process running that file. Since changes to mmap'ed files are immediately visible to other processes, any processes running that file would almost certainly crash in a very mysterious way. Identifying the cause of these random crashes took us a few days.
Rejecting writes to an executable file that is currently running is a well-known behavior, and Linux had operated that way for a very long time. So, I don’t believe relying on this behavior was our mistake; rather, I see this as a regression in the Linux kernel.
Here is a bug report to the mold linker: https://github.com/rui314/mold/issues/1361
#regzbot introduced: 2a010c41285345da60cece35575b4e0af7e7bf44