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Michal Hocko 2f064f3485 mm: make page pfmemalloc check more robust ... Commit c48a11c7ad ("netvm: propagate page->pfmemalloc to skb") added checks for page->pfmemalloc to __skb_fill_page_desc(): if (page->pfmemalloc && !page->mapping) skb->pfmemalloc = true; It assumes page->mapping == NULL implies that page->pfmemalloc can be trusted. However, __delete_from_page_cache() can set set page->mapping to NULL and leave page->index value alone. Due to being in union, a non-zero page->index will be interpreted as true page->pfmemalloc. So the assumption is invalid if the networking code can see such a page. And it seems it can. We have encountered this with a NFS over loopback setup when such a page is attached to a new skbuf. There is no copying going on in this case so the page confuses __skb_fill_page_desc which interprets the index as pfmemalloc flag and the network stack drops packets that have been allocated using the reserves unless they are to be queued on sockets handling the swapping which is the case here and that leads to hangs when the nfs client waits for a response from the server which has been dropped and thus never arrive. The struct page is already heavily packed so rather than finding another hole to put it in, let's do a trick instead. We can reuse the index again but define it to an impossible value (-1UL). This is the page index so it should never see the value that large. Replace all direct users of page->pfmemalloc by page_is_pfmemalloc which will hide this nastiness from unspoiled eyes. The information will get lost if somebody wants to use page->index obviously but that was the case before and the original code expected that the information should be persisted somewhere else if that is really needed (e.g. what SLAB and SLUB do). [akpm@linux-foundation.org: fix blooper in slub] Fixes: c48a11c7ad ("netvm: propagate page->pfmemalloc to skb") Signed-off-by: Michal Hocko <mhocko@suse.com> Debugged-by: Vlastimil Babka <vbabka@suse.com> Debugged-by: Jiri Bohac <jbohac@suse.com> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: David Miller <davem@davemloft.net> Acked-by: Mel Gorman <mgorman@suse.de> Cc: <stable@vger.kernel.org> [3.6+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		10 years ago
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acpi	Additional ACPICA material for v4.2-rc1	10 years ago
asm-generic	mm: clean up per architecture MM hook header files	10 years ago
clocksource	…
crypto	crypto: rng - Do not free default RNG when it becomes unused	10 years ago
drm	drm/edid: add function to help find SADs	10 years ago
dt-bindings	The changes to the common clock framework for 4.2 are dominated by new	10 years ago
keys	…
kvm	…
linux	mm: make page pfmemalloc check more robust	10 years ago
math-emu	…
media	media fixes for v4.2-rc8	10 years ago
memory	…
misc	…
net	net: sched: fix refcount imbalance in actions	10 years ago
pcmcia	…
ras	tracing: add trace event for memory-failure	10 years ago
rdma	IB: Add rdma_cap_ib_switch helper and use where appropriate	10 years ago
rxrpc	…
scsi	Merge branch 'for-4.2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata	10 years ago
soc	Merge branch 'for-linus' of git://ftp.arm.linux.org.uk/~rmk/linux-arm	10 years ago
sound	ASoC: topology: Add Kconfig option for topology	10 years ago
target	iscsi-target: Fix iscsit_start_kthreads failure OOPs	10 years ago
trace	Merge branch 'for-linus-4.2' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs	10 years ago
uapi	sound fixes for 4.2-final	10 years ago
video	Merge branch 'drm-next' of git://people.freedesktop.org/~airlied/linux	10 years ago
xen	…
Kbuild	…