From: Matt Benjamin <mbenjamin@redhat.com>
Date: Fri, 19 Jan 2018 18:05:27 +0000 (-0500)
Subject: rgw_file: alternate fix deadlock on lru eviction
X-Git-Tag: v13.0.2~470^2
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=refs%2Fpull%2F20034%2Fhead;p=ceph.git

rgw_file: alternate fix deadlock on lru eviction

This change is an alternate fix for two problems found and fixed
by Yao Zongyou <yaozongyou@vip.qq.com>.

The deadlock can be avoided just by not taking it in the recycle
case, which invariantly holds the lock.

The invalidation of the insert iterator by the recyle-path unlink
we'd like to handle as a condition in order to preserve the cached
insertion point optimization we get in the common case.  (The
original behavior was, indeed, incorrect.)

Based on feedback from Yao, removed the RGWFileHandle dtor version
of the unlink check, which I think happened twice.

Signed-off-by: Matt Benjamin <mbenjamin@redhat.com>
---

diff --git a/src/common/cohort_lru.h b/src/common/cohort_lru.h
index bd4fa9570978..edd3e38828a9 100644
--- a/src/common/cohort_lru.h
+++ b/src/common/cohort_lru.h
@@ -32,6 +32,7 @@ namespace cohort {
     /* public flag values */
     constexpr uint32_t FLAG_NONE = 0x0000;
     constexpr uint32_t FLAG_INITIAL = 0x0001;
+    constexpr uint32_t FLAG_RECYCLE = 0x0002;
 
     enum class Edge : std::uint8_t
     {
@@ -232,12 +233,14 @@ namespace cohort {
 	  delete tdo;
       } /* unref */
 
-      Object* insert(ObjectFactory* fac, Edge edge, uint32_t flags) {
+      Object* insert(ObjectFactory* fac, Edge edge, uint32_t& flags) {
 	/* use supplied functor to re-use an evicted object, or
 	 * allocate a new one of the descendant type */
 	Object* o = evict_block();
-	if (o)
+	if (o) {
 	  fac->recycle(o); /* recycle existing object */
+	  flags |= FLAG_RECYCLE;
+	}
 	else
 	  o = fac->alloc(); /* get a new one */
 
diff --git a/src/rgw/rgw_file.cc b/src/rgw/rgw_file.cc
index d37f05be30c6..b35630bc9a12 100644
--- a/src/rgw/rgw_file.cc
+++ b/src/rgw/rgw_file.cc
@@ -954,10 +954,6 @@ namespace rgw {
   }
 
   RGWFileHandle::~RGWFileHandle() {
-    /* in the non-delete case, handle may still be in handle table */
-    if (fh_hook.is_linked()) {
-      fs->fh_cache.remove(fh.fh_hk.object, this, FHCache::FLAG_LOCK);
-    }
     /* cond-unref parent */
     if (parent && (! parent->is_mount())) {
       /* safe because if parent->unref causes its deletion,
@@ -1007,9 +1003,11 @@ namespace rgw {
     lsubdout(fs->get_context(), rgw, 17)
       << __func__ << " " << *this
       << dendl;
-    /* remove if still in fh_cache */
+    /* in the non-delete case, handle may still be in handle table */
     if (fh_hook.is_linked()) {
-      fs->fh_cache.remove(fh.fh_hk.object, this, FHCache::FLAG_LOCK);
+      /* in this case, we are being called from a context which holds
+       * the partition lock */
+      fs->fh_cache.remove(fh.fh_hk.object, this, FHCache::FLAG_NONE);
     }
     return true;
   } /* RGWFileHandle::reclaim */
diff --git a/src/rgw/rgw_file.h b/src/rgw/rgw_file.h
index 4843c95dc987..d4e5333e0100 100644
--- a/src/rgw/rgw_file.h
+++ b/src/rgw/rgw_file.h
@@ -1061,16 +1061,25 @@ namespace rgw {
 	/* make or re-use handle */
 	RGWFileHandle::Factory prototype(this, parent, fhk,
 					 obj_name, CREATE_FLAGS(flags));
+	uint32_t iflags{cohort::lru::FLAG_INITIAL};
 	fh = static_cast<RGWFileHandle*>(
 	  fh_lru.insert(&prototype,
 			cohort::lru::Edge::MRU,
-			cohort::lru::FLAG_INITIAL));
+			iflags));
 	if (fh) {
 	  /* lock fh (LATCHED) */
 	  if (flags & RGWFileHandle::FLAG_LOCK)
 	    fh->mtx.lock();
-	  /* inserts, releasing latch */
-	  fh_cache.insert_latched(fh, lat, RGWFileHandle::FHCache::FLAG_UNLOCK);
+	  if (likely(! (iflags & cohort::lru::FLAG_RECYCLE))) {
+	    /* inserts at cached insert iterator, releasing latch */
+	    fh_cache.insert_latched(
+	      fh, lat, RGWFileHandle::FHCache::FLAG_UNLOCK);
+	  } else {
+	    /* recycle step invalidates Latch */
+	    fh_cache.insert(
+	      fhk.fh_hk.object, fh, RGWFileHandle::FHCache::FLAG_NONE);
+	    lat.lock->unlock(); /* !LATCHED */
+	  }
 	  get<1>(fhr) |= RGWFileHandle::FLAG_CREATE;
 	  /* ref parent (non-initial ref cannot fail on valid object) */
 	  if (! parent->is_mount()) {