[Devel] [PATCH vz9 1/2] dm-ploop: fix self-deadlock in ploop_prepare_reloc_index_wb()

[Konstantin Khorenko]

  NMI watchdog: Watchdog detected hard LOCKUP on cpu 6
  RIP: 0010:native_queued_spin_lock_slowpath+0x20d/0x2b0

  Call Trace:
   dump_stack_lvl+0x57/0x81
   validate_chain.cold+0x157/0x16a
   __lock_acquire+0xbb1/0x1900
   lock_acquire+0x1da/0x640
   _raw_spin_lock_irqsave+0x43/0x90
   ploop_allocate_cluster+0x12f/0x8c0 [ploop]
   ploop_alloc_cluster.isra.0+0xf7/0x1f0 [ploop]
   ploop_prepare_reloc_index_wb+0x2ab/0x4e0 [ploop]
   ploop_grow_relocate_cluster+0x849/0xcc0 [ploop]
   ploop_process_resize_cmd+0x65/0x430 [ploop]
   ploop_resize+0x415/0x680 [ploop]
   ploop_message+0x420/0xc90 [ploop]
   target_message+0x453/0x5e0 [dm_mod]
   ctl_ioctl+0x41f/0x6a0 [dm_mod]
   dm_ctl_ioctl+0xa/0x20 [dm_mod]
   __x64_sys_ioctl+0x12b/0x1a0
   do_syscall_64+0x5c/0x90
   entry_SYSCALL_64_after_hwframe+0x77/0xe1

ploop_prepare_reloc_index_wb() aquires ploop->bat_lock and calls
(holding the lock) ploop_alloc_cluster(), which also aquires
ploop->bat_lock => deadlock.

  ploop_prepare_reloc_index_wb
    spin_lock_irq(&ploop->bat_lock);
    ploop_alloc_cluster
      ploop_allocate_cluster
        spin_lock_irqsave(&ploop->bat_lock, flags);

Let's move ploop_alloc_cluster() out of the bat_lock, this is safe as
MD_UPDATING bit checked and set under the lock protects us from parallel
ploop_alloc_cluster() execution for a pertucular md_page.
And if the function is called in parallel for different md_page, it's
also OK as new cluster is searched in the bitmask under the bat_lock, so
same cluster wil never be found and "allocated" in parallel.

Fixes: 9caa1af11b0a ("dm-ploop: fix and rework md updates")
https://virtuozzo.atlassian.net/browse/VSTOR-107975

Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>

Feature: dm-ploop: ploop target driver
---
 drivers/md/dm-ploop-map.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index 35085a04ca5f..5a2ef5691405 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -2746,6 +2746,7 @@ int ploop_prepare_reloc_index_wb(struct ploop *ploop,
 	add_to_wblist = ploop_md_make_dirty(ploop, md);
 
 	piwb = md->piwb;
+	spin_unlock_irq(&ploop->bat_lock);
 
 	if (dst_clu) {
 		/*
@@ -2759,7 +2760,6 @@ int ploop_prepare_reloc_index_wb(struct ploop *ploop,
 		if (err)
 			goto out_reset;
 	}
-	spin_unlock_irq(&ploop->bat_lock);
 
 	*ret_md = md;
 	*add_for_wb = add_to_wblist ? 1 : 0;
@@ -2768,6 +2768,7 @@ int ploop_prepare_reloc_index_wb(struct ploop *ploop,
 
 out_reset:
 	ploop_break_bat_update(ploop, md, piwb);
+	spin_lock_irq(&ploop->bat_lock);
 out_error:
 	if (add_to_wblist)
 		clear_bit(MD_DIRTY, &md->status);
-- 
2.43.5