Messages in this thread Patch in this message | | | Date | Thu, 20 Apr 2006 12:48:52 -0700 | From | Andrew Morton <> | Subject | Re: BUG at drivers/md/kcopyd.c:146 (was: [PATCH 1/9] device-mapper snapshot: load metadata on creation) |
| |
(restored Juergen's cc)
Alasdair G Kergon <agk@redhat.com> wrote: > > On Sat, Apr 15, 2006 at 01:19:51PM +0200, Juergen Kreileder wrote: > > I'm using devmapper 1.02.03 and lvm2 2.02.02 with 2.6.16.2, > > nevertheless my logical volumes locked up three time when removing > > snapshots so far. Twice I got BUG at drivers/md/kcopyd.c:146, the > > third time logging stopped at the first lvremove. > > > 2.6.15 and earlier kernels in combination with older tools worked fine > > over the last year. > > I found several bugs in the snapshot code when I reviewed it, > including (thankfully hard-to-trigger) silent data corruption. > > Patches went into 2.6.17-rc1. [There's one unfinished patch > outstanding for a theoretical race that I've only been able to > reproduce under artificial conditions.] > > > kernel BUG at drivers/md/kcopyd.c:146! > > Probably needs this patch (12th March): > > dm snapshot: fix kcopyd destructor >
Thanks, I've appended a copy here.
Juergen, can you please test this?
Alasdair, what are your thoughts on backporting this to 2.6.16.x?
From: Alasdair G Kergon <agk@redhat.com>
Before removing a snapshot, wait for the completion of any kcopyd jobs using it.
Do this by maintaining a count (nr_jobs) of how many outstanding jobs each kcopyd_client has.
The snapshot destructor first unregisters the snapshot so that no new kcopyd jobs (created by writes to the origin) will reference that particular snapshot. kcopyd_client_destroy() is now run next to wait for the completion of any outstanding jobs before the snapshot exception structures (that those jobs reference) are freed.
Signed-off-by: Alasdair G Kergon <agk@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> ---
drivers/md/dm-snap.c | 6 +++++- drivers/md/kcopyd.c | 17 ++++++++++++++++- 2 files changed, 21 insertions(+), 2 deletions(-)
diff -puN drivers/md/dm-snap.c~dm-snapshot-fix-kcopyd-destructor drivers/md/dm-snap.c --- devel/drivers/md/dm-snap.c~dm-snapshot-fix-kcopyd-destructor 2006-03-27 01:10:28.000000000 -0800 +++ devel-akpm/drivers/md/dm-snap.c 2006-03-27 01:10:28.000000000 -0800 @@ -559,8 +559,12 @@ static void snapshot_dtr(struct dm_targe { struct dm_snapshot *s = (struct dm_snapshot *) ti->private; + /* Prevent further origin writes from using this snapshot. */ + /* After this returns there can be no new kcopyd jobs. */ unregister_snapshot(s); + kcopyd_client_destroy(s->kcopyd_client); + exit_exception_table(&s->pending, pending_cache); exit_exception_table(&s->complete, exception_cache); @@ -569,7 +573,7 @@ static void snapshot_dtr(struct dm_targe dm_put_device(ti, s->origin); dm_put_device(ti, s->cow); - kcopyd_client_destroy(s->kcopyd_client); + kfree(s); } diff -puN drivers/md/kcopyd.c~dm-snapshot-fix-kcopyd-destructor drivers/md/kcopyd.c --- devel/drivers/md/kcopyd.c~dm-snapshot-fix-kcopyd-destructor 2006-03-27 01:10:28.000000000 -0800 +++ devel-akpm/drivers/md/kcopyd.c 2006-03-27 01:10:28.000000000 -0800 @@ -44,6 +44,9 @@ struct kcopyd_client { struct page_list *pages; unsigned int nr_pages; unsigned int nr_free_pages; + + wait_queue_head_t destroyq; + atomic_t nr_jobs; }; static struct page_list *alloc_pl(void) @@ -292,10 +295,15 @@ static int run_complete_job(struct kcopy int read_err = job->read_err; unsigned int write_err = job->write_err; kcopyd_notify_fn fn = job->fn; + struct kcopyd_client *kc = job->kc; - kcopyd_put_pages(job->kc, job->pages); + kcopyd_put_pages(kc, job->pages); mempool_free(job, _job_pool); fn(read_err, write_err, context); + + if (atomic_dec_and_test(&kc->nr_jobs)) + wake_up(&kc->destroyq); + return 0; } @@ -430,6 +438,7 @@ static void do_work(void *ignored) */ static void dispatch_job(struct kcopyd_job *job) { + atomic_inc(&job->kc->nr_jobs); push(&_pages_jobs, job); wake(); } @@ -669,6 +678,9 @@ int kcopyd_client_create(unsigned int nr return r; } + init_waitqueue_head(&kc->destroyq); + atomic_set(&kc->nr_jobs, 0); + client_add(kc); *result = kc; return 0; @@ -676,6 +688,9 @@ int kcopyd_client_create(unsigned int nr void kcopyd_client_destroy(struct kcopyd_client *kc) { + /* Wait for completion of all jobs submitted by this client. */ + wait_event(kc->destroyq, !atomic_read(&kc->nr_jobs)); + dm_io_put(kc->nr_pages); client_free_pages(kc); client_del(kc); _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |