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    SubjectRe: Simple script that locks up my box with recent kernels
    On Tue, Nov 21 2006, Linus Torvalds wrote:
    > I don't think we use any irq-disable locking in the VM itself, but I could
    > imagine some nasty situation with the block device layer getting into a
    > deadlock with interrupts disabled when it runs out of queue entries and
    > cannot allocate more memory..

    Not likely. Request allocation is done with GFP_NOIO and backed by a
    memory pool, so as long the vm doesn't go totally nuts because
    __GFP_WAIT is set, we should be safe there. If it did go crazy, I
    suspect a sysrq-t would still work.

    If bouncing is involved for swap, we do have a potential deadlock issue
    that isn't fixed yet. I just whipped up this completely untested patch,
    it should shed some light on that issue.

    diff --git a/mm/bounce.c b/mm/bounce.c
    index e4b62d2..f75eb37 100644
    --- a/mm/bounce.c
    +++ b/mm/bounce.c
    @@ -20,6 +20,7 @@ #define POOL_SIZE 64
    #define ISA_POOL_SIZE 16

    static mempool_t *page_pool, *isa_page_pool;
    +static struct bio_set *bounce_bio_set;

    static __init int init_emergency_pool(void)
    @@ -31,6 +32,9 @@ static __init int init_emergency_pool(vo
    if (!i.totalhigh)
    return 0;

    + bounce_bio_set = bioset_create(1, 1, 0);
    + BUG_ON(!bounce_bio_set);
    page_pool = mempool_create_page_pool(POOL_SIZE, 0);
    printk("highmem bounce pool size: %d pages\n", POOL_SIZE);
    @@ -190,6 +194,11 @@ static int bounce_end_io_read_isa(struct
    return 0;

    +static void bounce_bio_destructor(struct bio *bio)
    + bio_free(bio, bounce_bio_set);
    static void __blk_queue_bounce(request_queue_t *q, struct bio **bio_orig,
    mempool_t *pool)
    @@ -210,8 +219,10 @@ static void __blk_queue_bounce(request_q
    * irk, bounce it
    - if (!bio)
    - bio = bio_alloc(GFP_NOIO, (*bio_orig)->bi_vcnt);
    + if (!bio) {
    + bio = bio_alloc_bioset(GFP_NOIO, (*bio_orig)->bi_vcnt, bounce_bio_set);
    + bio->bi_destructor = bounce_bio_destructor;
    + }

    to = bio->bi_io_vec + i;

    Jens Axboe

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      Last update: 2006-11-22 09:05    [W:0.029 / U:136.844 seconds]
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