On Tue, May 20, 2014 at 09:46:43AM -0700, Tony Luck wrote:
> When Linux sees an "action optional" machine check (where h/w has
> reported an error that is not in the current execution path) we
> generally do not want to signal a process, since most processes
> do not have a SIGBUS handler - we'd just prematurely terminate the
> process for a problem that they might never actually see.
>
> task_early_kill() decides whether to consider a process - and it
> checks whether this specific process has been marked for early signals
> with "prctl", or if the system administrator has requested early
> signals for all processes using /proc/sys/vm/memory_failure_early_kill.
>
> But for MF_ACTION_REQUIRED case we must not defer. The error is in
> the execution path of the current thread so we must send the SIGBUS
> immediatley.
>
> Fix by passing a flag argument through collect_procs*() to
> task_early_kill() so it knows whether we can defer or must
> take action.
>
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Thanks,
Naoya Horiguchi
> ---
> mm/memory-failure.c | 21 ++++++++++++---------
> 1 file changed, 12 insertions(+), 9 deletions(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 642c8434b166..f0967f72991c 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -380,10 +380,12 @@ static void kill_procs(struct list_head *to_kill, int forcekill, int trapno,
> }
> }
>
> -static int task_early_kill(struct task_struct *tsk)
> +static int task_early_kill(struct task_struct *tsk, int force_early)
> {
> if (!tsk->mm)
> return 0;
> + if (force_early)
> + return 1;
> if (tsk->flags & PF_MCE_PROCESS)
> return !!(tsk->flags & PF_MCE_EARLY);
> return sysctl_memory_failure_early_kill;
> @@ -393,7 +395,7 @@ static int task_early_kill(struct task_struct *tsk)
> * Collect processes when the error hit an anonymous page.
> */
> static void collect_procs_anon(struct page *page, struct list_head *to_kill,
> - struct to_kill **tkc)
> + struct to_kill **tkc, int force_early)
> {
> struct vm_area_struct *vma;
> struct task_struct *tsk;
> @@ -409,7 +411,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
> for_each_process (tsk) {
> struct anon_vma_chain *vmac;
>
> - if (!task_early_kill(tsk))
> + if (!task_early_kill(tsk, force_early))
> continue;
> anon_vma_interval_tree_foreach(vmac, &av->rb_root,
> pgoff, pgoff) {
> @@ -428,7 +430,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
> * Collect processes when the error hit a file mapped page.
> */
> static void collect_procs_file(struct page *page, struct list_head *to_kill,
> - struct to_kill **tkc)
> + struct to_kill **tkc, int force_early)
> {
> struct vm_area_struct *vma;
> struct task_struct *tsk;
> @@ -439,7 +441,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
> for_each_process(tsk) {
> pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
>
> - if (!task_early_kill(tsk))
> + if (!task_early_kill(tsk, force_early))
> continue;
>
> vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff,
> @@ -465,7 +467,8 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
> * First preallocate one tokill structure outside the spin locks,
> * so that we can kill at least one process reasonably reliable.
> */
> -static void collect_procs(struct page *page, struct list_head *tokill)
> +static void collect_procs(struct page *page, struct list_head *tokill,
> + int force_early)
> {
> struct to_kill *tk;
>
> @@ -476,9 +479,9 @@ static void collect_procs(struct page *page, struct list_head *tokill)
> if (!tk)
> return;
> if (PageAnon(page))
> - collect_procs_anon(page, tokill, &tk);
> + collect_procs_anon(page, tokill, &tk, force_early);
> else
> - collect_procs_file(page, tokill, &tk);
> + collect_procs_file(page, tokill, &tk, force_early);
> kfree(tk);
> }
>
> @@ -963,7 +966,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
> * there's nothing that can be done.
> */
> if (kill)
> - collect_procs(ppage, &tokill);
> + collect_procs(ppage, &tokill, flags & MF_ACTION_REQUIRED);
>
> ret = try_to_unmap(ppage, ttu);
> if (ret != SWAP_SUCCESS)
> --
> 1.8.4.1
>
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