This is a note to let you know that I've just added the patch titled percpu: fix synchronization between chunk->map_extend_work and chunk destruction to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: percpu-fix-synchronization-between-chunk-map_extend_work-and-chunk-destruction.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 4f996e234dad488e5d9ba0858bc1bae12eff82c3 Mon Sep 17 00:00:00 2001 From: Tejun Heo <tj@xxxxxxxxxx> Date: Wed, 25 May 2016 11:48:25 -0400 Subject: percpu: fix synchronization between chunk->map_extend_work and chunk destruction From: Tejun Heo <tj@xxxxxxxxxx> commit 4f996e234dad488e5d9ba0858bc1bae12eff82c3 upstream. Atomic allocations can trigger async map extensions which is serviced by chunk->map_extend_work. pcpu_balance_work which is responsible for destroying idle chunks wasn't synchronizing properly against chunk->map_extend_work and may end up freeing the chunk while the work item is still in flight. This patch fixes the bug by rolling async map extension operations into pcpu_balance_work. Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> Reported-and-tested-by: Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> Reported-by: Vlastimil Babka <vbabka@xxxxxxx> Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx> Fixes: 9c824b6a172c ("percpu: make sure chunk->map array has available space") Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/percpu.c | 57 ++++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 36 insertions(+), 21 deletions(-) --- a/mm/percpu.c +++ b/mm/percpu.c @@ -110,7 +110,7 @@ struct pcpu_chunk { int map_used; /* # of map entries used before the sentry */ int map_alloc; /* # of map entries allocated */ int *map; /* allocation map */ - struct work_struct map_extend_work;/* async ->map[] extension */ + struct list_head map_extend_list;/* on pcpu_map_extend_chunks */ void *data; /* chunk data */ int first_free; /* no free below this */ @@ -164,6 +164,9 @@ static DEFINE_MUTEX(pcpu_alloc_mutex); / static struct list_head *pcpu_slot __read_mostly; /* chunk list slots */ +/* chunks which need their map areas extended, protected by pcpu_lock */ +static LIST_HEAD(pcpu_map_extend_chunks); + /* * The number of empty populated pages, protected by pcpu_lock. The * reserved chunk doesn't contribute to the count. @@ -397,13 +400,19 @@ static int pcpu_need_to_extend(struct pc { int margin, new_alloc; + lockdep_assert_held(&pcpu_lock); + if (is_atomic) { margin = 3; if (chunk->map_alloc < - chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW && - pcpu_async_enabled) - schedule_work(&chunk->map_extend_work); + chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW) { + if (list_empty(&chunk->map_extend_list)) { + list_add_tail(&chunk->map_extend_list, + &pcpu_map_extend_chunks); + pcpu_schedule_balance_work(); + } + } } else { margin = PCPU_ATOMIC_MAP_MARGIN_HIGH; } @@ -469,20 +478,6 @@ out_unlock: return 0; } -static void pcpu_map_extend_workfn(struct work_struct *work) -{ - struct pcpu_chunk *chunk = container_of(work, struct pcpu_chunk, - map_extend_work); - int new_alloc; - - spin_lock_irq(&pcpu_lock); - new_alloc = pcpu_need_to_extend(chunk, false); - spin_unlock_irq(&pcpu_lock); - - if (new_alloc) - pcpu_extend_area_map(chunk, new_alloc); -} - /** * pcpu_fit_in_area - try to fit the requested allocation in a candidate area * @chunk: chunk the candidate area belongs to @@ -742,7 +737,7 @@ static struct pcpu_chunk *pcpu_alloc_chu chunk->map_used = 1; INIT_LIST_HEAD(&chunk->list); - INIT_WORK(&chunk->map_extend_work, pcpu_map_extend_workfn); + INIT_LIST_HEAD(&chunk->map_extend_list); chunk->free_size = pcpu_unit_size; chunk->contig_hint = pcpu_unit_size; @@ -1131,6 +1126,7 @@ static void pcpu_balance_workfn(struct w if (chunk == list_first_entry(free_head, struct pcpu_chunk, list)) continue; + list_del_init(&chunk->map_extend_list); list_move(&chunk->list, &to_free); } @@ -1148,6 +1144,25 @@ static void pcpu_balance_workfn(struct w pcpu_destroy_chunk(chunk); } + /* service chunks which requested async area map extension */ + do { + int new_alloc = 0; + + spin_lock_irq(&pcpu_lock); + + chunk = list_first_entry_or_null(&pcpu_map_extend_chunks, + struct pcpu_chunk, map_extend_list); + if (chunk) { + list_del_init(&chunk->map_extend_list); + new_alloc = pcpu_need_to_extend(chunk, false); + } + + spin_unlock_irq(&pcpu_lock); + + if (new_alloc) + pcpu_extend_area_map(chunk, new_alloc); + } while (chunk); + /* * Ensure there are certain number of free populated pages for * atomic allocs. Fill up from the most packed so that atomic @@ -1646,7 +1661,7 @@ int __init pcpu_setup_first_chunk(const */ schunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0); INIT_LIST_HEAD(&schunk->list); - INIT_WORK(&schunk->map_extend_work, pcpu_map_extend_workfn); + INIT_LIST_HEAD(&schunk->map_extend_list); schunk->base_addr = base_addr; schunk->map = smap; schunk->map_alloc = ARRAY_SIZE(smap); @@ -1675,7 +1690,7 @@ int __init pcpu_setup_first_chunk(const if (dyn_size) { dchunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0); INIT_LIST_HEAD(&dchunk->list); - INIT_WORK(&dchunk->map_extend_work, pcpu_map_extend_workfn); + INIT_LIST_HEAD(&dchunk->map_extend_list); dchunk->base_addr = base_addr; dchunk->map = dmap; dchunk->map_alloc = ARRAY_SIZE(dmap); Patches currently in stable-queue which might be from tj@xxxxxxxxxx are queue-4.4/writeback-use-higher-precision-calculation-in-domain_dirty_limits.patch queue-4.4/percpu-fix-synchronization-between-synchronous-map-extension-and-chunk-destruction.patch queue-4.4/percpu-fix-synchronization-between-chunk-map_extend_work-and-chunk-destruction.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html