On Mon, Jan 27, 2020 at 11:11:00AM +0100, Grzegorz Halat wrote: > Memory management subsystem performs various checks at runtime, > if an inconsistency is detected then such event is being logged and kernel > continues to run. While debugging such problems it is helpful to collect > memory dump as early as possible. Currently, there is no easy way to panic > kernel when such error is detected. > > It was proposed[1] to panic the kernel if panic_on_oops is set but this > approach was not accepted. One of alternative proposals was introduction of > a new sysctl. > > The patch adds panic_on_mm_error sysctl. If the sysctl is set then the > kernel will be crashed when an inconsistency is detected by memory > management. This currently means panic when bad page or bad PTE > is detected(this may be extended to other places in MM). > > Another use case of this sysctl may be in security-wise environments, > it may be more desired to crash machine than continue to run with > potentially damaged data structures. > > [1] https://marc.info/?l=linux-mm&m=142649500728327&w=2 > > Signed-off-by: Grzegorz Halat <ghalat@xxxxxxxxxx> > --- > Documentation/admin-guide/sysctl/kernel.rst | 12 ++++++++++++ > include/linux/kernel.h | 1 + > kernel/sysctl.c | 9 +++++++++ > mm/memory.c | 7 +++++++ > mm/page_alloc.c | 4 +++- > 5 files changed, 32 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst > index def074807cee..2fecd6b2547e 100644 > --- a/Documentation/admin-guide/sysctl/kernel.rst > +++ b/Documentation/admin-guide/sysctl/kernel.rst > @@ -61,6 +61,7 @@ show up in /proc/sys/kernel: > - overflowgid > - overflowuid > - panic > +- panic_on_mm_error > - panic_on_oops > - panic_on_stackoverflow > - panic_on_unrecovered_nmi > @@ -611,6 +612,17 @@ an IO error. > and you can use this option to take a crash dump. > > > +panic_on_mm_error: > +============== > + > +Controls the kernel's behaviour when inconsistency is detected > +by memory management code, for example bad page state or bad PTE. > + > +0: try to continue operation. > + > +1: panic immediately. > + > + > panic_on_oops: > ============== > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index 0d9db2a14f44..5f9d408512ff 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -518,6 +518,7 @@ extern int oops_in_progress; /* If set, an oops, panic(), BUG() or die() is in > extern int panic_timeout; > extern unsigned long panic_print; > extern int panic_on_oops; > +extern int panic_on_mm_error; > extern int panic_on_unrecovered_nmi; > extern int panic_on_io_nmi; > extern int panic_on_warn; > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 70665934d53e..6477e1cce28b 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -1238,6 +1238,15 @@ static struct ctl_table kern_table[] = { > .extra1 = SYSCTL_ZERO, > .extra2 = SYSCTL_ONE, > }, > + { > + .procname = "panic_on_mm_error", > + .data = &panic_on_mm_error, > + .maxlen = sizeof(int), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax, > + .extra1 = SYSCTL_ZERO, > + .extra2 = SYSCTL_ONE, > + }, > #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON) > { > .procname = "timer_migration", > diff --git a/mm/memory.c b/mm/memory.c > index 45442d9a4f52..cce74ff39447 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -71,6 +71,7 @@ > #include <linux/dax.h> > #include <linux/oom.h> > #include <linux/numa.h> > +#include <linux/module.h> > > #include <trace/events/kmem.h> > > @@ -88,6 +89,8 @@ > #warning Unfortunate NUMA and NUMA Balancing config, growing page-frame for last_cpupid. > #endif > > +int panic_on_mm_error __read_mostly; > + > #ifndef CONFIG_NEED_MULTIPLE_NODES > /* use the per-pgdat data instead for discontigmem - mbligh */ > unsigned long max_mapnr; > @@ -543,6 +546,10 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr, > vma->vm_ops ? vma->vm_ops->fault : NULL, > vma->vm_file ? vma->vm_file->f_op->mmap : NULL, > mapping ? mapping->a_ops->readpage : NULL); > + > + print_modules(); > + if (panic_on_mm_error) > + panic("Bad page map detected"); > dump_stack(); > add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE); > } > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index d047bf7d8fd4..2ea6a65ba011 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -643,9 +643,11 @@ static void bad_page(struct page *page, const char *reason, > if (bad_flags) > pr_alert("bad because of flags: %#lx(%pGp)\n", > bad_flags, &bad_flags); > - dump_page_owner(page); > > + dump_page_owner(page); > print_modules(); > + if (panic_on_mm_error) > + panic("Bad page state detected"); > dump_stack(); > out: > /* Leave bad fields for debug, except PageBuddy could make trouble */ > -- > 2.21.1 > Reviewed-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxx> -- Best regards, Oleksandr Natalenko (post-factum) Senior Software Maintenance Engineer
