diff options
Diffstat (limited to 'debian/patches/0002-fatfs-use-a-seperate-lock-to-protect-nodehash.patch')
| -rw-r--r-- | debian/patches/0002-fatfs-use-a-seperate-lock-to-protect-nodehash.patch | 303 |
1 files changed, 303 insertions, 0 deletions
diff --git a/debian/patches/0002-fatfs-use-a-seperate-lock-to-protect-nodehash.patch b/debian/patches/0002-fatfs-use-a-seperate-lock-to-protect-nodehash.patch new file mode 100644 index 00000000..6c3f2b49 --- /dev/null +++ b/debian/patches/0002-fatfs-use-a-seperate-lock-to-protect-nodehash.patch @@ -0,0 +1,303 @@ +From ecca4f4c8e32ff1774892718446566c2c5c36979 Mon Sep 17 00:00:00 2001 +From: Justus Winter <4winter@informatik.uni-hamburg.de> +Date: Tue, 13 May 2014 15:14:53 +0200 +Subject: [PATCH 2/4] fatfs: use a seperate lock to protect nodehash + +Previously, fatfs used diskfs_node_refcnt_lock to serialize access to +the nodehash. + +Use a separate lock to protect nodehash. Adjust the reference +counting accordingly. Every node in the nodehash carries a light +reference. When we are asked to give up that light reference, we +reacquire our lock momentarily to check whether someone else +reacquired a reference through the nodehash. + +* fatfs/inode.c (nodecache_lock): New lock. +(diskfs_cached_lookup): Use a separate lock to protect nodehash. +Adjust the reference counting accordingly. +(ifind): Likewise. +(diskfs_node_iterate): Likewise. +(diskfs_node_norefs): Move the code removing the node from nodehash... +(diskfs_try_dropping_softrefs): ... here, where we check whether +someone reacquired a reference, and if so hold on to our light +reference. +--- + fatfs/inode.c | 146 ++++++++++++++++++++++++++++++++++++++++------------------ + 1 file changed, 101 insertions(+), 45 deletions(-) + +diff --git a/fatfs/inode.c b/fatfs/inode.c +index ed6f3f0..c3997d0 100644 +--- a/fatfs/inode.c ++++ b/fatfs/inode.c +@@ -44,8 +44,19 @@ + #define INOHASH(ino) (((unsigned)(ino))%INOHSZ) + #endif + ++/* The nodehash is a cache of nodes. ++ ++ Access to nodehash and nodehash_nr_items is protected by ++ nodecache_lock. ++ ++ Every node in the nodehash carries a light reference. When we are ++ asked to give up that light reference, we reacquire our lock ++ momentarily to check whether someone else reacquired a reference ++ through the nodehash. */ + static struct node *nodehash[INOHSZ]; + static size_t nodehash_nr_items; ++/* nodecache_lock must be acquired before diskfs_node_refcnt_lock. */ ++static pthread_rwlock_t nodecache_lock = PTHREAD_RWLOCK_INITIALIZER; + + static error_t read_node (struct node *np, vm_address_t buf); + +@@ -58,33 +69,38 @@ inode_init () + nodehash[n] = 0; + } + ++/* Lookup node with inode number INUM. Returns NULL if the node is ++ not found in the node cache. */ ++static struct node * ++lookup (ino_t inum) ++{ ++ struct node *np; ++ for (np = nodehash[INOHASH(inum)]; np; np = np->dn->hnext) ++ if (np->cache_id == inum) ++ return np; ++ return NULL; ++} ++ + /* Fetch inode INUM, set *NPP to the node structure; gain one user + reference and lock the node. */ + error_t + diskfs_cached_lookup (ino64_t inum, struct node **npp) + { + error_t err; +- struct node *np; ++ struct node *np, *tmp; + struct disknode *dn; + +- pthread_spin_lock (&diskfs_node_refcnt_lock); +- for (np = nodehash[INOHASH(inum)]; np; np = np->dn->hnext) +- if (np->cache_id == inum) +- { +- np->references++; +- pthread_spin_unlock (&diskfs_node_refcnt_lock); +- pthread_mutex_lock (&np->lock); +- *npp = np; +- return 0; +- } ++ pthread_rwlock_rdlock (&nodecache_lock); ++ np = lookup (inum); ++ if (np) ++ goto gotit; ++ pthread_rwlock_unlock (&nodecache_lock); + + /* Format specific data for the new node. */ + dn = malloc (sizeof (struct disknode)); + if (! dn) +- { +- pthread_spin_unlock (&diskfs_node_refcnt_lock); +- return ENOMEM; +- } ++ return ENOMEM; ++ + dn->pager = 0; + dn->first = 0; + dn->last = 0; +@@ -102,15 +118,25 @@ diskfs_cached_lookup (ino64_t inum, struct node **npp) + pthread_mutex_lock (&np->lock); + + /* Put NP in NODEHASH. */ ++ pthread_rwlock_wrlock (&nodecache_lock); ++ tmp = lookup (inum); ++ if (tmp) ++ { ++ /* We lost a race. */ ++ diskfs_nput (np); ++ np = tmp; ++ goto gotit; ++ } ++ + dn->hnext = nodehash[INOHASH(inum)]; + if (dn->hnext) + dn->hnext->dn->hprevp = &dn->hnext; + dn->hprevp = &nodehash[INOHASH(inum)]; + nodehash[INOHASH(inum)] = np; ++ diskfs_nref_light (np); + nodehash_nr_items += 1; ++ pthread_rwlock_unlock (&nodecache_lock); + +- pthread_spin_unlock (&diskfs_node_refcnt_lock); +- + /* Get the contents of NP off disk. */ + err = read_node (np, 0); + +@@ -121,6 +147,13 @@ diskfs_cached_lookup (ino64_t inum, struct node **npp) + *npp = np; + return 0; + } ++ ++ gotit: ++ diskfs_nref (np); ++ pthread_rwlock_unlock (&nodecache_lock); ++ pthread_mutex_lock (&np->lock); ++ *npp = np; ++ return 0; + } + + /* Fetch inode INUM, set *NPP to the node structure; +@@ -133,24 +166,23 @@ diskfs_cached_lookup_in_dirbuf (int inum, struct node **npp, vm_address_t buf) + struct node *np; + struct disknode *dn; + +- pthread_spin_lock (&diskfs_node_refcnt_lock); ++ pthread_rwlock_rdlock (&nodecache_lock); + for (np = nodehash[INOHASH(inum)]; np; np = np->dn->hnext) + if (np->cache_id == inum) + { +- np->references++; +- pthread_spin_unlock (&diskfs_node_refcnt_lock); ++ diskfs_nref (np); ++ pthread_rwlock_unlock (&nodecache_lock); + pthread_mutex_lock (&np->lock); + *npp = np; + return 0; + } ++ pthread_rwlock_unlock (&nodecache_lock); + + /* Format specific data for the new node. */ + dn = malloc (sizeof (struct disknode)); + if (! dn) +- { +- pthread_spin_unlock (&diskfs_node_refcnt_lock); +- return ENOMEM; +- } ++ return ENOMEM; ++ + dn->pager = 0; + dn->first = 0; + dn->last = 0; +@@ -168,15 +200,16 @@ diskfs_cached_lookup_in_dirbuf (int inum, struct node **npp, vm_address_t buf) + pthread_mutex_lock (&np->lock); + + /* Put NP in NODEHASH. */ ++ pthread_rwlock_wrlock (&nodecache_lock); + dn->hnext = nodehash[INOHASH(inum)]; + if (dn->hnext) + dn->hnext->dn->hprevp = &dn->hnext; + dn->hprevp = &nodehash[INOHASH(inum)]; + nodehash[INOHASH(inum)] = np; ++ diskfs_nref_light (np); + nodehash_nr_items += 1; ++ pthread_rwlock_unlock (&nodecache_lock); + +- pthread_spin_unlock (&diskfs_node_refcnt_lock); +- + /* Get the contents of NP off disk. */ + err = read_node (np, buf); + +@@ -196,17 +229,12 @@ ifind (ino_t inum) + { + struct node *np; + +- pthread_spin_lock (&diskfs_node_refcnt_lock); +- for (np = nodehash[INOHASH(inum)]; np; np = np->dn->hnext) +- { +- if (np->cache_id != inum) +- continue; ++ pthread_rwlock_rdlock (&nodecache_lock); ++ np = lookup (inum); ++ pthread_rwlock_unlock (&nodecache_lock); + +- assert (np->references); +- pthread_spin_unlock (&diskfs_node_refcnt_lock); +- return np; +- } +- assert (0); ++ assert (np); ++ return np; + } + + /* The last reference to a node has gone away; drop it from the hash +@@ -216,11 +244,6 @@ diskfs_node_norefs (struct node *np) + { + struct cluster_chain *last = np->dn->first; + +- *np->dn->hprevp = np->dn->hnext; +- if (np->dn->hnext) +- np->dn->hnext->dn->hprevp = np->dn->hprevp; +- nodehash_nr_items -= 1; +- + while (last) + { + struct cluster_chain *next = last->next; +@@ -251,6 +274,35 @@ diskfs_node_norefs (struct node *np) + void + diskfs_try_dropping_softrefs (struct node *np) + { ++ pthread_rwlock_wrlock (&nodecache_lock); ++ if (np->dn->hnext != NULL) ++ { ++ /* Check if someone reacquired a reference through the ++ nodehash. */ ++ unsigned int references; ++ pthread_spin_lock (&diskfs_node_refcnt_lock); ++ references = np->references; ++ pthread_spin_unlock (&diskfs_node_refcnt_lock); ++ ++ /* An additional reference is acquired by libdiskfs across calls ++ to diskfs_try_dropping_softrefs. */ ++ if (references > 1) ++ { ++ /* A reference was reacquired through a hash table lookup. ++ It's fine, we didn't touch anything yet. */ ++ pthread_rwlock_unlock (&nodecache_lock); ++ return; ++ } ++ ++ *np->dn->hprevp = np->dn->hnext; ++ if (np->dn->hnext) ++ np->dn->hnext->dn->hprevp = np->dn->hprevp; ++ np->dn->hnext = NULL; ++ nodehash_nr_items -= 1; ++ diskfs_nrele_light (np); ++ } ++ pthread_rwlock_unlock (&nodecache_lock); ++ + drop_pager_softrefs (np); + } + +@@ -554,12 +606,12 @@ diskfs_node_iterate (error_t (*fun)(struct node *)) + size_t num_nodes; + struct node *node, **node_list, **p; + +- pthread_spin_lock (&diskfs_node_refcnt_lock); ++ pthread_rwlock_rdlock (&nodecache_lock); + + /* We must copy everything from the hash table into another data structure + to avoid running into any problems with the hash-table being modified + during processing (normally we delegate access to hash-table with +- diskfs_node_refcnt_lock, but we can't hold this while locking the ++ nodecache_lock, but we can't hold this while locking the + individual node locks). */ + + num_nodes = nodehash_nr_items; +@@ -570,10 +622,14 @@ diskfs_node_iterate (error_t (*fun)(struct node *)) + for (node = nodehash[n]; node; node = node->dn->hnext) + { + *p++ = node; +- node->references++; ++ ++ /* We acquire a hard reference for node, but without using ++ diskfs_nref. We do this so that diskfs_new_hardrefs will not ++ get called. */ ++ node->references++; + } + +- pthread_spin_unlock (&diskfs_node_refcnt_lock); ++ pthread_rwlock_unlock (&nodecache_lock); + + p = node_list; + while (num_nodes-- > 0) +-- +2.0.0.rc2 + |