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    SubjectRe: [PATCH] exec/fs: fix initial stack reservation
    Date
    > In message <20100215155821.7298.A69D9226@jp.fujitsu.com> you 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?
    >
    > Actually, I think we can just get rid of min() line altogether.
    > expand_stack checks to make sure the stack is getting bigger, otherwise
    > it does nothing. We don't need to bother with this check.
    >
    > The below works for me on UML x86_64 and ppc64 64k and 4k pages.

    OK, Right you are.
    Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>


    >
    > 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 attempting ensure the stack is not
    > reduced in size, we ended up not changing the stack at all.
    >
    > This size reduction check is not necessary as the expand_stack call does
    > this already.
    >
    > This caused a regression in UML resulting in most guest processes being
    > killed.
    >
    > Signed-off-by: Michael Neuling <mikey@neuling.org>
    > cc: <stable@kernel.org>
    > ---
    > fs/exec.c | 1 -
    > 1 file changed, 1 deletion(-)
    >
    > Index: linux-2.6-ozlabs/fs/exec.c
    > ===================================================================
    > --- linux-2.6-ozlabs.orig/fs/exec.c
    > +++ linux-2.6-ozlabs/fs/exec.c
    > @@ -637,7 +637,6 @@ int setup_arg_pages(struct linux_binprm
    > * 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;





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