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    SubjectRe: 2.6.33-rc8 breaks UML with Restrict initial stack space expansion to rlimit
    On Mon, Feb 15, 2010 at 03:59:26PM +0900, KOSAKI Motohiro wrote:
    >>
    >>
    >> In message <20100214164023.GA2726@jm.kir.nu> you wrote:
    >> > It looks like the commit 803bf5ec259941936262d10ecc84511b76a20921
    >> > (fs/exec.c: restrict initial stack space expansion to rlimit) broke my
    >> > user mode Linux setup by somehow preventing system setup from running
    >> > properly (or killing some processes that try to mount things, etc.).
    >> > This commit turned up as the reason based on git bisect and reverting it
    >> > fixes my UML test setup (Ubuntu 9.10 on both host and in UML and AMD64
    >> > arch for both). I have no idea what exactly would be the main cause for
    >> > this issue, but this looks like a somewhat unfortunately timed
    >> > regression in 2.6.33-rc8.
    >> >
    >> > The failed run shows like this (with current linux-2.6.git):
    >> >
    >> > ...
    >> > EXT3-fs (ubda): mounted filesystem with writeback data mode
    >> > VFS: Mounted root (ext3 filesystem) readonly on device 98:0.
    >> > IRQ 3/console-write: IRQF_DISABLED is not guaranteed on shared IRQs
    >> > IRQ 2/console: IRQF_DISABLED is not guaranteed on shared IRQs
    >> > IRQ 10/winch: IRQF_DISABLED is not guaranteed on shared IRQs
    >> > IRQ 10/winch: IRQF_DISABLED is not guaranteed on shared IRQs
    >> > mountall: mount /sys/kernel/debug [218] killed by KILL signal
    >> > mountall: Filesystem could not be mounted: /sys/kernel/debug
    >> > mountall: mount /dev [219] killed by KILL signal
    >> > mountall: Filesystem could not be mounted: /dev
    >> > mountall: mount /tmp [220] killed by KILL signal
    >> > mountall: Filesystem could not be mounted: /tmp
    >> > mountall: mount /var/lock [222] killed by KILL signal
    >> > mountall: Filesystem could not be mounted: /var/lock
    >> > ...
    >> >
    >> >
    >> > With 803bf5ec reverted, UML comes up and the output looks like this:
    >> >
    >> > ...
    >> > EXT3-fs (ubda): mounted filesystem with writeback data mode
    >> > VFS: Mounted root (ext3 filesystem) readonly on device 98:0.
    >> > IRQ 3/console-write: IRQF_DISABLED is not guaranteed on shared IRQs
    >> > IRQ 2/console: IRQF_DISABLED is not guaranteed on shared IRQs
    >> > IRQ 10/winch: IRQF_DISABLED is not guaranteed on shared IRQs
    >> > IRQ 10/winch: IRQF_DISABLED is not guaranteed on shared IRQs
    >> > init: procps main process (226) terminated with status 255
    >> > fsck from util-linux-ng 2.16
    >> > ...
    >>
    >> Jouni,
    >>
    >> I can reproduce this now.
    >>
    >> We got the logic wrong in one of the cleanups and hence we aren't
    >> actually changing the stack reservation ever, when we intended on
    >> allocating up to 20 new pages.
    >>
    >> The:
    >> rlim_stack = min(rlim_stack, stack_size);
    >> always chooses stack_size hence we end up not changing the stack at all.
    >> This seems to cause fatal problems on UML, but is obviously not what was
    >> intended for archs as well.
    >>
    >> The following works for me on PPC64 64k and 4k pages and UML on x86_64.
    >>
    >> Let me know if it fixes it for you also.
    >>
    >> Mikey
    >>
    >>
    >> exec/fs: fix initial stack reservation
    >>
    >> 803bf5ec259941936262d10ecc84511b76a20921 (fs/exec.c: restrict initial
    >> stack space expansion to rlimit) attempts to limit the initial stack to
    >> 20*PAGE_SIZE. Unfortunately, in also attempting ensure the stack is not
    >> reduced in size, we ended up not changing the stack at all.
    >>
    >> This caused a regression in UML resulting in most guest processes to be
    >> killed.
    >>
    >> Signed-off-by: Michael Neuling <mikey@neuling.org>
    >> cc: <stable@kernel.org>
    >>
    >> diff --git a/fs/exec.c b/fs/exec.c
    >> index e95c692..e0e7b3c 100644
    >> --- a/fs/exec.c
    >> +++ b/fs/exec.c
    >> @@ -637,15 +637,16 @@ int setup_arg_pages(struct linux_binprm *bprm,
    >> * will align it up.
    >> */
    >> rlim_stack = rlimit(RLIMIT_STACK) & PAGE_MASK;
    >> - rlim_stack = min(rlim_stack, stack_size);
    >> #ifdef CONFIG_STACK_GROWSUP
    >> if (stack_size + stack_expand > rlim_stack)
    >> - stack_base = vma->vm_start + rlim_stack;
    >> + /* Expand only to rlimit, making sure not to shrink it */
    >> + stack_base = vma->vm_start + max(rlim_stack,stack_size);
    >> else
    >> stack_base = vma->vm_end + stack_expand;
    >> #else
    >> if (stack_size + stack_expand > rlim_stack)
    >> - stack_base = vma->vm_end - rlim_stack;
    >> + /* Expand only to rlimit, making sure not to shrink it */
    >> + stack_base = vma->vm_end - max(rlim_stack,stack_size);
    >> else
    >> stack_base = vma->vm_start - stack_expand;
    >> #endif
    >
    >- rlim_stack = min(rlim_stack, stack_size);
    >+ /* Expand only to rlimit, making sure not to shrink it */
    >+ rlim_stack = max(rlim_stack, stack_size);
    >
    >is better fix?
    >

    Odd. If this is the right fix, 'stack_size" will be able to exceed
    stack rlimit, then Michael's previous rlimit patch will be useless.
    Am I missing something?



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