Hi Aurelien & Faidon,
Quoting Aurelien Jarno (2021-10-24 14:35:33)
> 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.Aurelien, I have no idea how you found this bug but thanks a ton for analyzing it and finding the right fix!! :D Faidon, maybe jemalloc could add a test that checks for this so that this problem does not show up in the tests of an unrelated package? Thanks! cheers, josch
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