On Mon, Mar 10, 2014 at 03:12:33PM +0100, Bart Van Assche wrote:
> Avoid that percpu_ida_alloc() hangs or crashes if there are still
> tags are available. Wait until a tag becomes available instead of
> giving up when running out of tags temporarily. This patch fixes
> the following kernel bug:
Hi Bart,
Few comments below, but the changelog does not correspond to the
actual change in 'Wait until a tag becomes available'.
> ------------[ cut here ]------------
> kernel BUG at lib/percpu_ida.c:81!
> invalid opcode: 0000 [#1] SMP
> RIP: 0010:[<ffffffff8120f00e>] [<ffffffff8120f00e>]
> percpu_ida_alloc+0x33e/0x370
> Call Trace:
> [<ffffffff811ef95f>] blk_mq_get_tag+0x2f/0x50
> [<ffffffff811ed79c>] blk_mq_alloc_rq.isra.17+0x1c/0x90
> [<ffffffff811eeb9b>] blk_mq_alloc_request_pinned+0x9b/0x110
> [<ffffffff811ef4c6>] blk_mq_make_request+0x426/0x480
> [<ffffffff811e28f0>] generic_make_request+0xc0/0x110
> [<ffffffff811e29ab>] submit_bio+0x6b/0x140
> [<ffffffff8117aabb>] _submit_bh+0x13b/0x220
> [<ffffffff8117d70f>] block_read_full_page+0x1ff/0x300
> [<ffffffff81181128>] blkdev_readpage+0x18/0x20
> [<ffffffff811067b7>] __do_page_cache_readahead+0x277/0x280
> [<ffffffff81106d1d>] force_page_cache_readahead+0x8d/0xc0
> [<ffffffff81106d9b>] page_cache_sync_readahead+0x4b/0x50
> [<ffffffff810fdf05>] generic_file_aio_read+0x4c5/0x700
> [<ffffffff8118147b>] blkdev_aio_read+0x4b/0x70
> [<ffffffff8114a28a>] do_sync_read+0x5a/0x90
> [<ffffffff8114a8cb>] vfs_read+0x9b/0x160
> [<ffffffff8114b389>] SyS_read+0x49/0xa0
> [<ffffffff81416049>] tracesys+0xd0/0xd5
> ---[ end trace cdd1a8a7968266cf ]---
>
> Signed-off-by: Bart Van Assche <bvanass...@acm.org>
> Cc: Kent Overstreet <k...@daterainc.com>
> Cc: Shaohua Li <s...@kernel.org>
> Cc: Christoph Hellwig <h...@lst.de>
> Cc: Jens Axboe <ax...@kernel.dk>
> Cc: Alexander Gordeev <agord...@redhat.com>
> Cc: Mike Christie <micha...@cs.wisc.edu>
> ---
> lib/percpu_ida.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/lib/percpu_ida.c b/lib/percpu_ida.c
> index 93d145e..170d27c 100644
> --- a/lib/percpu_ida.c
> +++ b/lib/percpu_ida.c
> @@ -73,7 +73,7 @@ static inline void steal_tags(struct percpu_ida *pool,
> if (cpu >= nr_cpu_ids) {
> cpu = cpumask_first(&pool->cpus_have_tags);
> if (cpu >= nr_cpu_ids)
> - BUG();
> + break;
I assume the BUG() above hits? If so, I am failing to understand how
the code gets here. Mind elaborate?
> }
>
> pool->cpu_last_stolen = cpu;
> @@ -189,6 +189,9 @@ int percpu_ida_alloc(struct percpu_ida *pool, int state)
> spin_unlock(&pool->lock);
> local_irq_restore(flags);
>
> + if (tags->nr_free)
> + wake_up(&pool->wait);
> +
How 'tags->nr_free' could be checked out of locks?
Why waking up another thread instead of returning the tag on this CPU?
Why 'percpu_max_size' threshold is ignored?
Anyway, IMHO the above BUG() indicates a problem elsewhere.
> if (tag >= 0 || state == TASK_RUNNING)
> break;
>
> --
> 1.8.4.5
>
--
Regards,
Alexander Gordeev
agord...@redhat.com
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