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commit 9c41f4eeb9d51f3ece20428d35a3ea32cf3b5622 upstream.
A vmalloc fault needs to sync up PGD/PTE entry from init_mm to current
task's "active_mm". ARC vmalloc fault handler however was using mm.
A vmalloc fault for non user task context (actually pre-userland, from
init thread's open for /dev/console) caused the handler to deref NULL mm
(for mm->pgd)
The reasons it worked so far is amazing:
1. By default (!SMP), vmalloc fault handler uses a cached value of PGD.
In SMP that MMU register is repurposed hence need for mm pointer deref.
2. In pre-3.12 SMP kernel, the problem triggering vmalloc didn't exist in
pre-userland code path - it was introduced with commit 20bafb3d23d108bc
"n_tty: Move buffers into n_tty_data"
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: Noam Camus <noamc@ezchip.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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