From 725a97e43ee945cc813fffd9e628e50d703b973b Mon Sep 17 00:00:00 2001 From: Lars Ellenberg Date: Sun, 19 Dec 2010 11:29:55 +0100 Subject: [PATCH] drbd: fix potential access of on-stack wait_queue_head_t after return I run into something declaring itself as "spinlock deadlock", BUG: spinlock lockup on CPU#1, kjournald/27816, ffff88000ad6bca0 Pid: 27816, comm: kjournald Tainted: G W 2.6.34.6 #2 Call Trace: [] do_raw_spin_lock+0x11e/0x14d [] _raw_spin_lock_irqsave+0x6a/0x81 [] ? __wake_up+0x22/0x50 [] __wake_up+0x22/0x50 [] bm_async_io_complete+0x258/0x299 [drbd] but the call traces do not fit at all, all other cpus are cpu_idle. I think it may be this race: drbd_bm_write_page wait_queue_head_t io_wait; atomic_t in_flight; bm_async_io submit_bio bm_async_io_complete if (atomic_dec_and_test(in_flight)) wait_event(io_wait, atomic_read(in_flight) == 0) return wake_up(io_wait) The wake_up now accesses the wait_queue_head_t spinlock, which is no longer valid, since the stack frame of drbd_bm_write_page has been clobbered now. Fix this by using struct completion, which does both the condition test as well as the wake_up inside its spinlock, so this race cannot happen. Signed-off-by: Philipp Reisner Signed-off-by: Lars Ellenberg --- drivers/block/drbd/drbd_bitmap.c | 38 ++++++++++++++++++-------------- 1 file changed, 22 insertions(+), 16 deletions(-) diff --git a/drivers/block/drbd/drbd_bitmap.c b/drivers/block/drbd/drbd_bitmap.c index 314a3632303b..25428bc28476 100644 --- a/drivers/block/drbd/drbd_bitmap.c +++ b/drivers/block/drbd/drbd_bitmap.c @@ -897,7 +897,7 @@ void drbd_bm_clear_all(struct drbd_conf *mdev) struct bm_aio_ctx { struct drbd_conf *mdev; atomic_t in_flight; - wait_queue_head_t io_wait; + struct completion done; unsigned flags; #define BM_AIO_COPY_PAGES 1 int error; @@ -948,7 +948,7 @@ static void bm_async_io_complete(struct bio *bio, int error) bio_put(bio); if (atomic_dec_and_test(&ctx->in_flight)) - wake_up(&ctx->io_wait); + complete(&ctx->done); } static void bm_page_io_async(struct bm_aio_ctx *ctx, int page_nr, int rw) __must_hold(local) @@ -1009,8 +1009,12 @@ static void bm_page_io_async(struct bm_aio_ctx *ctx, int page_nr, int rw) __must */ static int bm_rw(struct drbd_conf *mdev, int rw, unsigned lazy_writeout_upper_idx) __must_hold(local) { - struct bm_aio_ctx ctx = - { .flags = lazy_writeout_upper_idx ? BM_AIO_COPY_PAGES : 0 }; + struct bm_aio_ctx ctx = { + .mdev = mdev, + .in_flight = ATOMIC_INIT(1), + .done = COMPLETION_INITIALIZER_ONSTACK(ctx.done), + .flags = lazy_writeout_upper_idx ? BM_AIO_COPY_PAGES : 0, + }; struct drbd_bitmap *b = mdev->bitmap; int num_pages, i, count = 0; unsigned long now; @@ -1031,10 +1035,6 @@ static int bm_rw(struct drbd_conf *mdev, int rw, unsigned lazy_writeout_upper_id num_pages = b->bm_number_of_pages; now = jiffies; - ctx.mdev = mdev; - atomic_set(&ctx.in_flight, 1); /* one extra ref */ - init_waitqueue_head(&ctx.io_wait); - ctx.error = 0; /* let the layers below us try to merge these bios... */ for (i = 0; i < num_pages; i++) { @@ -1060,8 +1060,13 @@ static int bm_rw(struct drbd_conf *mdev, int rw, unsigned lazy_writeout_upper_id cond_resched(); } - atomic_dec(&ctx.in_flight); /* drop the extra ref */ - wait_event(ctx.io_wait, atomic_read(&ctx.in_flight) == 0); + /* + * We initialize ctx.in_flight to one to make sure bm_async_io_complete + * will not complete() early, and decrement / test it here. If there + * are still some bios in flight, we need to wait for them here. + */ + if (!atomic_dec_and_test(&ctx.in_flight)) + wait_for_completion(&ctx.done); dev_info(DEV, "bitmap %s of %u pages took %lu jiffies\n", rw == WRITE ? "WRITE" : "READ", count, jiffies - now); @@ -1133,19 +1138,20 @@ int drbd_bm_write_lazy(struct drbd_conf *mdev, unsigned upper_idx) __must_hold(l */ int drbd_bm_write_page(struct drbd_conf *mdev, unsigned int idx) __must_hold(local) { - struct bm_aio_ctx ctx = { .flags = BM_AIO_COPY_PAGES, }; + struct bm_aio_ctx ctx = { + .mdev = mdev, + .in_flight = ATOMIC_INIT(1), + .done = COMPLETION_INITIALIZER_ONSTACK(ctx.done), + .flags = BM_AIO_COPY_PAGES, + }; if (bm_test_page_unchanged(mdev->bitmap->bm_pages[idx])) { dynamic_dev_dbg(DEV, "skipped bm page write for idx %u\n", idx); return 0; } - ctx.mdev = mdev; - atomic_set(&ctx.in_flight, 1); - init_waitqueue_head(&ctx.io_wait); - bm_page_io_async(&ctx, idx, WRITE_SYNC); - wait_event(ctx.io_wait, atomic_read(&ctx.in_flight) == 0); + wait_for_completion(&ctx.done); if (ctx.error) drbd_chk_io_error(mdev, 1, true); -- 2.34.1