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Date: Thu, 5 Oct 2017 08:49:01 +0200 From: Vlastimil Babka <vbabka@...e.cz> To: Johannes Weiner <hannes@...xchg.org>, Andrew Morton <akpm@...ux-foundation.org> Cc: Alan Cox <alan@...yncelyn.cymru>, Christoph Hellwig <hch@....de>, Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, kernel-team@...com Subject: Re: [PATCH 1/2] Revert "vmalloc: back off when the current task is killed" On 10/04/2017 08:59 PM, Johannes Weiner wrote: > This reverts commit 5d17a73a2ebeb8d1c6924b91e53ab2650fe86ffb and > commit 171012f561274784160f666f8398af8b42216e1f. > > 5d17a73a2ebe ("vmalloc: back off when the current task is killed") > made all vmalloc allocations from a signal-killed task fail. We have > seen crashes in the tty driver from this, where a killed task exiting > tries to switch back to N_TTY, fails n_tty_open because of the vmalloc > failing, and later crashes when dereferencing tty->disc_data. > > Arguably, relying on a vmalloc() call to succeed in order to properly > exit a task is not the most robust way of doing things. There will be > a follow-up patch to the tty code to fall back to the N_NULL ldisc. > > But the justification to make that vmalloc() call fail like this isn't > convincing, either. The patch mentions an OOM victim exhausting the > memory reserves and thus deadlocking the machine. But the OOM killer > is only one, improbable source of fatal signals. It doesn't make sense > to fail allocations preemptively with plenty of memory in most cases. > > The patch doesn't mention real-life instances where vmalloc sites > would exhaust memory, which makes it sound more like a theoretical > issue to begin with. But just in case, the OOM access to memory > reserves has been restricted on the allocator side in cd04ae1e2dc8 > ("mm, oom: do not rely on TIF_MEMDIE for memory reserves access"), > which should take care of any theoretical concerns on that front. > > Revert this patch, and the follow-up that suppresses the allocation > warnings when we fail the allocations due to a signal. > > Signed-off-by: Johannes Weiner <hannes@...xchg.org> Acked-by: Vlastimil Babka <vbabka@...e.cz> > --- > mm/vmalloc.c | 6 ------ > 1 file changed, 6 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 8a43db6284eb..673942094328 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -1695,11 +1695,6 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask, > for (i = 0; i < area->nr_pages; i++) { > struct page *page; > > - if (fatal_signal_pending(current)) { > - area->nr_pages = i; > - goto fail_no_warn; > - } > - > if (node == NUMA_NO_NODE) > page = alloc_page(alloc_mask|highmem_mask); > else > @@ -1723,7 +1718,6 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask, > warn_alloc(gfp_mask, NULL, > "vmalloc: allocation failure, allocated %ld of %ld bytes", > (area->nr_pages*PAGE_SIZE), area->size); > -fail_no_warn: > vfree(area->addr); > return NULL; > } >
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