From: Mikulas Patocka Date: Fri, 10 May 2013 13:37:15 +0000 (+0100) Subject: dm bufio: avoid a possible __vmalloc deadlock X-Git-Tag: v3.2.46~70 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4725f1715429f75fa5f053dbe05575d08aeb5967;p=pandora-kernel.git dm bufio: avoid a possible __vmalloc deadlock commit 502624bdad3dba45dfaacaf36b7d83e39e74b2d2 upstream. This patch uses memalloc_noio_save to avoid a possible deadlock in dm-bufio. (it could happen only with large block size, at most PAGE_SIZE << MAX_ORDER (typically 8MiB). __vmalloc doesn't fully respect gfp flags. The specified gfp flags are used for allocation of requested pages, structures vmap_area, vmap_block and vm_struct and the radix tree nodes. However, the kernel pagetables are allocated always with GFP_KERNEL. Thus the allocation of pagetables can recurse back to the I/O layer and cause a deadlock. This patch uses the function memalloc_noio_save to set per-process PF_MEMALLOC_NOIO flag and the function memalloc_noio_restore to restore it. When this flag is set, all allocations in the process are done with implied GFP_NOIO flag, thus the deadlock can't happen. This should be backported to stable kernels, but they don't have the PF_MEMALLOC_NOIO flag and memalloc_noio_save/memalloc_noio_restore functions. So, PF_MEMALLOC should be set and restored instead. Signed-off-by: Mikulas Patocka Signed-off-by: Alasdair G Kergon [bwh: Backported to 3.2 as recommended] Signed-off-by: Ben Hutchings --- Reading git-diff-tree failed