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As part of vmalloc() a __pte_alloc_kernel() allocation may occur. This internal allocation does not honor the gfp flags passed to vmalloc(). This means even when vmalloc(GFP_NOFS) is called it is possible that a synchronous reclaim will occur. This reclaim can trigger file IO which can result in a deadlock. This issue can be avoided by explicitly setting PF_MEMALLOC on the process to subvert synchronous reclaim when vmalloc() is called with !__GFP_FS. An example stack of the deadlock can be found here (1), along with the upstream kernel bug (2), and the original bug discussion on the linux-mm mailing list (3). This code can be properly autoconf'ed when the upstream bug is fixed. 1) http://github.com/behlendorf/zfs/issues/labels/Vmalloc#issue/133 2) http://bugzilla.kernel.org/show_bug.cgi?id=30702 3) http://marc.info/?l=linux-mm&m=128942194520631&w=4 |
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