On Mon, Nov 11, 2024 at 9:02 PM Thorsten Leemhuis <regressions@xxxxxxxxxxxxx> wrote: > > [adding a few CCs, dropping stable] > > On 28.10.24 12:15, Rui Ueyama wrote: > > 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/?id=2a010c412853). > > FWIW, that is 2a010c41285345 ("fs: don't block i_writecount during > exec") [v6.11-rc1] from Christian Brauner. > > > 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 > > Thx for the report. I might be missing something, but from here it looks > like nothing happened. So please allow me to ask: > > What's the status? Did anyone look into this? Is this sill happening? Ping? I think this is a fairly major kernel regression. We can't ask all our mold linker users to upgrade their linker before upgrading their kernel. Isn't "Never break userland" the kernel's policy? I wonder why no action or even a discussion has taken place so far.
