* matoro (matoro_mailinglist_kernel@xxxxxxxxx) wrote: > On 2023-11-11 16:27, Sam James wrote: > > Helge Deller <deller@xxxxxx> writes: > > > > > On 11/11/23 07:31, matoro wrote: > > > > Hi Helge, I have bisected a regression in 6.6 which is causing > > > > userspace segfaults at a significantly increased rate in kernel 6.6. > > > > There seems to be a pathological case triggered by the ninja build > > > > tool. The test case I have been using is cmake with ninja backend to > > > > attempt to build the nghttp2 package. In 6.6, this segfaults, not at > > > > the same location every time, but with enough reliability that I was > > > > able to use it as a bisection regression case, including immediately > > > > after a reboot. In the kernel log, these show up as "trap #15: Data > > > > TLB miss fault" messages. Now these messages can and do show up in > > > > 6.5 causing segfaults, but never immediately after a reboot and > > > > infrequently enough that the system is stable. With kernel 6.6 I am > > > > completely unable to build nghttp2 under any circumstances. > > > > > > > > I have bisected this down to the following commit: > > > > > > > > $ git bisect good > > > > 3033cd4307681c60db6d08f398a64484b36e0b0f is the first bad commit > > > > commit 3033cd4307681c60db6d08f398a64484b36e0b0f > > > > Author: Helge Deller <deller@xxxxxx> > > > > Date: Sat Aug 19 00:53:28 2023 +0200 > > > > > > > > parisc: Use generic mmap top-down layout and brk randomization > > > > > > > > parisc uses a top-down layout by default that exactly fits > > > > the generic > > > > functions, so get rid of arch specific code and use the > > > > generic version > > > > by selecting ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT. > > > > > > > > Note that on parisc the stack always grows up and a "unlimited stack" > > > > simply means that the value as defined in > > > > CONFIG_STACK_MAX_DEFAULT_SIZE_MB > > > > should be used. So RLIM_INFINITY is not an indicator to use > > > > the legacy > > > > memory layout. > > > > > > > > Signed-off-by: Helge Deller <deller@xxxxxx> > > > > > > > > arch/parisc/Kconfig | 17 +++++++++++++ > > > > arch/parisc/kernel/process.c | 14 ----------- > > > > arch/parisc/kernel/sys_parisc.c | 54 > > > > +---------------------------------------- > > > > mm/util.c | 5 +++- > > > > 4 files changed, 22 insertions(+), 68 deletions(-) > > > > > > Thanks for your report! > > > I think it's quite unlikely that this patch introduces such a bad > > > regression. > > > I'd suspect some other bad commmit, but I'll try to reproduce. > > > > matoro, does a revert apply cleanly? Does it help? > > Yes, I just tested this and it cleanly reverts on linux-6.6.y and the revert > does fix the issue. Helge: In that patch is: diff --git a/mm/util.c b/mm/util.c index dd12b9531ac4c..8810206444977 100644 --- a/mm/util.c +++ b/mm/util.c @@ -396,7 +396,10 @@ static int mmap_is_legacy(struct rlimit *rlim_stack) if (current->personality & ADDR_COMPAT_LAYOUT) return 1; - if (rlim_stack->rlim_cur == RLIM_INFINITY) + /* On parisc the stack always grows up - so a unlimited stack should + * not be an indicator to use the legacy memory layout. */ + if (rlim_stack->rlim_cur == RLIM_INFINITY && + !IS_ENABLED(CONFIG_STACK_GROWSUP)) return 1; return sysctl_legacy_va_layout; is that: '!IS_ENABLED(CONFIG_STACK_GROWSUP))' the right way around? That feels inverted to me; non-parisc don't have that config set, so !IS_ENABLED... is true, so they return 1 instead of checking the flag? Dave > > > > > > In any case, do you have CONFIG_BPF_JIT enabled? If so, could you try > > > to reproduce with CONFIG_BPF_JIT disabled? > > > The JIT is quite new in v6.6 and I did face some crashes and disabling > > > it helped me so far. > > > > > > > I have tried applying ad4aa06e1d92b06ed56c7240252927bd60632efe > > > > ("parisc: Add nop instructions after TLB inserts") on top of 6.6, but > > > > it does NOT fix the issue. > > > > > > Ok. > > > > > > Helge -- -----Open up your eyes, open up your mind, open up your code ------- / Dr. David Alan Gilbert | Running GNU/Linux | Happy \ \ dave @ treblig.org | | In Hex / \ _________________________|_____ http://www.treblig.org |_______/