Messages in this thread Patch in this message | | | From | Kamal Mostafa <> | Subject | [PATCH 35/78] dm bufio: avoid a possible __vmalloc deadlock | Date | Tue, 28 May 2013 14:19:44 -0700 |
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3.8.13.1 -stable review patch. If anyone has any objections, please let me know.
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From: Mikulas Patocka <mpatocka@redhat.com>
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 <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- drivers/md/dm-bufio.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c index 64eff90..5d2c26e 100644 --- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -319,6 +319,9 @@ static void __cache_size_refresh(void) static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask, enum data_mode *data_mode) { + unsigned noio_flag; + void *ptr; + if (c->block_size <= DM_BUFIO_BLOCK_SIZE_SLAB_LIMIT) { *data_mode = DATA_MODE_SLAB; return kmem_cache_alloc(DM_BUFIO_CACHE(c), gfp_mask); @@ -332,7 +335,26 @@ static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask, } *data_mode = DATA_MODE_VMALLOC; - return __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL); + + /* + * __vmalloc allocates the data pages and auxiliary structures with + * gfp_flags that were specified, but pagetables are always allocated + * with GFP_KERNEL, no matter what was specified as gfp_mask. + * + * Consequently, we must set per-process flag PF_MEMALLOC_NOIO so that + * all allocations done by this process (including pagetables) are done + * as if GFP_NOIO was specified. + */ + + if (gfp_mask & __GFP_NORETRY) + noio_flag = memalloc_noio_save(); + + ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL); + + if (gfp_mask & __GFP_NORETRY) + memalloc_noio_restore(noio_flag); + + return ptr; } /* -- 1.8.1.2
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