On 2021-10-24 11:26, Aurelien Jarno wrote:
> On 2021-10-23 08:12, Johannes Schauer Marin Rodrigues wrote:
> > Package: fakechroot
> > Version: 2.20.1-1
> > Severity: normal
> > Control: affects -1 + jemalloc
> >
> > Hi,
> >
> > libjemalloc and fakechroot do not play well together on arm64 and
> > riscv64. Faidon managed to analyze the situation. It follows what they
> > found out:
> >
> > I got a backtrace (see below) by:
> > 1) attempting a normal build; killing it when it reaches t/jemalloc.t
> > 2) cd test; ./t/jemalloc.t
> > 3) gdb -p ($pidof cat)
> >
> > This is a deadlock, by malloc() being invoked in the code path for malloc().
> > Something tries to malloc(), jemalloc tries to initialize itself, which in
> > turn
> > means trying to open() /sys/kernel/mm/transparent_hugepage/enabled, but
> > open()
> > is LD_PRELOADed to fakechroot, which tries to initialize itself, which in
> > turn
> > tries to malloc memory.
> >
> > I'm not entirely sure why that happens yet, or why it only happens on
> > arm64. I
> > believe it is unrelated to the previous bug, #918742.
>
> The common point of arm64 and riscv64 (and a few new architectures) is
> that they lack the older syscalls that can be replaced by newer one. In
> that case they lack the open syscall, which can be replaced by openat.
>
> jemalloc tries to query /sys/kernel/mm/transparent_hugepage/enabled
> directly through a syscall if available, without going through glibc as
> can be seen in src/pages.c:562:
>
> | #if defined(JEMALLOC_USE_SYSCALL) && defined(SYS_open)
> | int fd = (int)syscall(SYS_open,
> | "/sys/kernel/mm/transparent_hugepage/enabled", O_RDONLY);
> | #else
> | int fd = open("/sys/kernel/mm/transparent_hugepage/enabled",
> O_RDONLY);
> | #endif
>
> I guess one fix or workaround would be to add support for the SYS_openat
> syscall as a fallback. Luckily this has already been done upstream:
>
> https://github.com/jemalloc/jemalloc/commit/6924f83cb21f75e1c892d8f469500e12f1a3f5a7#diff-e2003bd99a76acf15d071c2fd49cfaeefae69debe6fc304a86f104b662da986c
I have rebuilt jemalloc with this patch on riscv64. I confirm that it
fixes the testsuite of fakechroot.
Regards,
Aurelien
--
Aurelien Jarno GPG: 4096R/1DDD8C9B
aurel...@aurel32.net http://www.aurel32.net
