On Thu, Jul 25, 2019 at 04:01:41PM -0600, Jane Chu wrote: > Mmap /dev/dax more than once, then read the poison location using address > from one of the mappings. The other mappings due to not having the page > mapped in will cause SIGKILLs delivered to the process. SIGKILL succeeds > over SIGBUS, so user process looses the opportunity to handle the UE. > > Although one may add MAP_POPULATE to mmap(2) to work around the issue, > MAP_POPULATE makes mapping 128GB of pmem several magnitudes slower, so > isn't always an option. > > Details - > > ndctl inject-error --block=10 --count=1 namespace6.0 > > ./read_poison -x dax6.0 -o 5120 -m 2 > mmaped address 0x7f5bb6600000 > mmaped address 0x7f3cf3600000 > doing local read at address 0x7f3cf3601400 > Killed > > Console messages in instrumented kernel - > > mce: Uncorrected hardware memory error in user-access at edbe201400 > Memory failure: tk->addr = 7f5bb6601000 > Memory failure: address edbe201: call dev_pagemap_mapping_shift > dev_pagemap_mapping_shift: page edbe201: no PUD > Memory failure: tk->size_shift == 0 > Memory failure: Unable to find user space address edbe201 in read_poison > Memory failure: tk->addr = 7f3cf3601000 > Memory failure: address edbe201: call dev_pagemap_mapping_shift > Memory failure: tk->size_shift = 21 > Memory failure: 0xedbe201: forcibly killing read_poison:22434 because of > failure to unmap corrupted page > => to deliver SIGKILL > Memory failure: 0xedbe201: Killing read_poison:22434 due to hardware memory > corruption > => to deliver SIGBUS > > Signed-off-by: Jane Chu <[email protected]> > Suggested-by: Naoya Horiguchi <[email protected]> > --- > mm/memory-failure.c | 22 +++++++++++++--------- > 1 file changed, 13 insertions(+), 9 deletions(-) > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index 51d5b20..f668c88 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -199,7 +199,6 @@ struct to_kill { > struct task_struct *tsk; > unsigned long addr; > short size_shift; > - char addr_valid; > }; > > /* > @@ -318,22 +317,27 @@ static void add_to_kill(struct task_struct *tsk, struct > page *p, > } > > tk->addr = page_address_in_vma(p, vma); > - tk->addr_valid = 1; > if (is_zone_device_page(p)) > tk->size_shift = dev_pagemap_mapping_shift(p, vma); > else > tk->size_shift = compound_order(compound_head(p)) + PAGE_SHIFT; > > /* > - * In theory we don't have to kill when the page was > - * munmaped. But it could be also a mremap. Since that's > - * likely very rare kill anyways just out of paranoia, but use > - * a SIGKILL because the error is not contained anymore. > + * Send SIGKILL if "tk->addr == -EFAULT". Also, as > + * "tk->size_shift" is always non-zero for !is_zone_device_page(), > + * so "tk->size_shift == 0" effectively checks no mapping on > + * ZONE_DEVICE. Indeed, when a devdax page is mmapped N times > + * to a process' address space, it's possible not all N VMAs > + * contain mappings for the page, but at least one VMA does. > + * Only deliver SIGBUS with payload derived from the VMA that > + * has a mapping for the page. > */ > - if (tk->addr == -EFAULT || tk->size_shift == 0) { > + if (tk->addr == -EFAULT) { ^ (sorry nitpicking...) there's a trailing whitespace. Otherwise looks good to me.
Acked-by: Naoya Horiguchi <[email protected]> > pr_info("Memory failure: Unable to find user space address %lx > in %s\n", > page_to_pfn(p), tsk->comm); > - tk->addr_valid = 0; > + } else if (tk->size_shift == 0) { > + kfree(tk); > + return; > } > > get_task_struct(tsk); > @@ -361,7 +365,7 @@ static void kill_procs(struct list_head *to_kill, int > forcekill, bool fail, > * make sure the process doesn't catch the > * signal and then access the memory. Just kill it. > */ > - if (fail || tk->addr_valid == 0) { > + if (fail || tk->addr == -EFAULT) { > pr_err("Memory failure: %#lx: forcibly killing > %s:%d because of failure to unmap corrupted page\n", > pfn, tk->tsk->comm, tk->tsk->pid); > do_send_sig_info(SIGKILL, SEND_SIG_PRIV, > -- > 1.8.3.1 > >
