Messages in this thread | | | From | "Huang\, Ying" <> | Subject | Re: [PATCH -mm -V7] mm, swap: fix race between swapoff and some swap operations | Date | Tue, 12 Feb 2019 14:40:48 +0800 |
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Daniel Jordan <daniel.m.jordan@oracle.com> writes:
> On Mon, Feb 11, 2019 at 04:38:46PM +0800, Huang, Ying wrote: >> +struct swap_info_struct *get_swap_device(swp_entry_t entry) >> +{ >> + struct swap_info_struct *si; >> + unsigned long type, offset; >> + >> + if (!entry.val) >> + goto out; > >> + type = swp_type(entry); >> + si = swap_type_to_swap_info(type); > > These lines can be collapsed into swp_swap_info if you want.
Yes. I can use that function to reduce another line from the patch. Thanks! Will do that.
>> + if (!si) >> + goto bad_nofile; >> + >> + preempt_disable(); >> + if (!(si->flags & SWP_VALID)) >> + goto unlock_out; > > After Hugh alluded to barriers, it seems the read of SWP_VALID could be > reordered with the write in preempt_disable at runtime. Without smp_mb() > between the two, couldn't this happen, however unlikely a race it is? > > CPU0 CPU1 > > __swap_duplicate() > get_swap_device() > // sees SWP_VALID set > swapoff > p->flags &= ~SWP_VALID; > spin_unlock(&p->lock); // pair w/ smp_mb > ... > stop_machine(...) > p->swap_map = NULL; > preempt_disable() > read NULL p->swap_map
Andrea has helped to explain this.
Best Regards, Huang, Ying
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