FreeBSD/Linux Kernel Cross Reference
sys/fs/lockd/svclock.c

     /*
      * linux/fs/lockd/svclock.c
      *
      * Handling of server-side locks, mostly of the blocked variety.
      * This is the ugliest part of lockd because we tread on very thin ice.
      * GRANT and CANCEL calls may get stuck, meet in mid-flight, etc.
      * IMNSHO introducing the grant callback into the NLM protocol was one
      * of the worst ideas Sun ever had. Except maybe for the idea of doing
      * NFS file locking at all.
     *
     * I'm trying hard to avoid race conditions by protecting most accesses
     * to a file's list of blocked locks through a semaphore. The global
     * list of blocked locks is not protected in this fashion however.
     * Therefore, some functions (such as the RPC callback for the async grant
     * call) move blocked locks towards the head of the list *while some other
     * process might be traversing it*. This should not be a problem in
     * practice, because this will only cause functions traversing the list
     * to visit some blocks twice.
     *
     * Copyright (C) 1996, Olaf Kirch <okir@monad.swb.de>
     */
    
    #include <linux/config.h>
    #include <linux/types.h>
    #include <linux/errno.h>
    #include <linux/kernel.h>
    #include <linux/sched.h>
    #include <linux/smp_lock.h>
    #include <linux/sunrpc/clnt.h>
    #include <linux/sunrpc/svc.h>
    #include <linux/lockd/nlm.h>
    #include <linux/lockd/lockd.h>
    
    #define NLMDBG_FACILITY         NLMDBG_SVCLOCK
    
    #ifdef CONFIG_LOCKD_V4
    #define nlm_deadlock    nlm4_deadlock
    #else
    #define nlm_deadlock    nlm_lck_denied
    #endif
    
    static void     nlmsvc_insert_block(struct nlm_block *block, unsigned long);
    static int      nlmsvc_remove_block(struct nlm_block *block);
    static void     nlmsvc_grant_callback(struct rpc_task *task);
    static void     nlmsvc_notify_blocked(struct file_lock *);
    
    /*
     * The list of blocked locks to retry
     */
    static struct nlm_block *       nlm_blocked;
    
    /*
     * Insert a blocked lock into the global list
     */
    static void
    nlmsvc_insert_block(struct nlm_block *block, unsigned long when)
    {
            struct nlm_block **bp, *b;
    
            dprintk("lockd: nlmsvc_insert_block(%p, %ld)\n", block, when);
            if (block->b_queued)
                    nlmsvc_remove_block(block);
            bp = &nlm_blocked;
            if (when != NLM_NEVER) {
                    if ((when += jiffies) == NLM_NEVER)
                            when ++;
                    while ((b = *bp) && time_before_eq(b->b_when,when) && b->b_when != NLM_NEVER)
                            bp = &b->b_next;
            } else
                    while ((b = *bp))
                            bp = &b->b_next;
    
            block->b_queued = 1;
            block->b_when = when;
            block->b_next = b;
            *bp = block;
    }
    
    /*
     * Remove a block from the global list
     */
    static int
    nlmsvc_remove_block(struct nlm_block *block)
    {
            struct nlm_block **bp, *b;
    
            if (!block->b_queued)
                    return 1;
            for (bp = &nlm_blocked; (b = *bp); bp = &b->b_next) {
                    if (b == block) {
                            *bp = block->b_next;
                            block->b_queued = 0;
                            return 1;
                    }
            }
    
            return 0;
    }
    
   /*
    * Find a block for a given lock and optionally remove it from
    * the list.
    */
   static struct nlm_block *
   nlmsvc_lookup_block(struct nlm_file *file, struct nlm_lock *lock, int remove)
   {
           struct nlm_block        **head, *block;
           struct file_lock        *fl;
   
           dprintk("lockd: nlmsvc_lookup_block f=%p pd=%d %Ld-%Ld ty=%d\n",
                                   file, lock->fl.fl_pid,
                                   (long long)lock->fl.fl_start,
                                   (long long)lock->fl.fl_end, lock->fl.fl_type);
           for (head = &nlm_blocked; (block = *head); head = &block->b_next) {
                   fl = &block->b_call.a_args.lock.fl;
                   dprintk("lockd: check f=%p pd=%d %Ld-%Ld ty=%d cookie=%x\n",
                                   block->b_file, fl->fl_pid,
                                   (long long)fl->fl_start,
                                   (long long)fl->fl_end, fl->fl_type,
                                   *(unsigned int*)(block->b_call.a_args.cookie.data));
                   if (block->b_file == file && nlm_compare_locks(fl, &lock->fl)) {
                           if (remove) {
                                   *head = block->b_next;
                                   block->b_queued = 0;
                           }
                           return block;
                   }
           }
   
           return NULL;
   }
   
   static inline int nlm_cookie_match(struct nlm_cookie *a, struct nlm_cookie *b)
   {
           if(a->len != b->len)
                   return 0;
           if(memcmp(a->data,b->data,a->len))
                   return 0;
           return 1;
   }
   
   /*
    * Find a block with a given NLM cookie.
    */
   static inline struct nlm_block *
   nlmsvc_find_block(struct nlm_cookie *cookie)
   {
           struct nlm_block *block;
   
           for (block = nlm_blocked; block; block = block->b_next) {
                   dprintk("cookie: head of blocked queue %p, block %p\n", 
                           nlm_blocked, block);
                   if (nlm_cookie_match(&block->b_call.a_args.cookie,cookie))
                           break;
           }
   
           return block;
   }
   
   /*
    * Create a block and initialize it.
    *
    * Note: we explicitly set the cookie of the grant reply to that of
    * the blocked lock request. The spec explicitly mentions that the client
    * should _not_ rely on the callback containing the same cookie as the
    * request, but (as I found out later) that's because some implementations
    * do just this. Never mind the standards comittees, they support our
    * logging industries.
    */
   static inline struct nlm_block *
   nlmsvc_create_block(struct svc_rqst *rqstp, struct nlm_file *file,
                                   struct nlm_lock *lock, struct nlm_cookie *cookie)
   {
           struct nlm_block        *block;
           struct nlm_host         *host;
           struct nlm_rqst         *call;
   
           /* Create host handle for callback */
           host = nlmclnt_lookup_host(&rqstp->rq_addr,
                                   rqstp->rq_prot, rqstp->rq_vers);
           if (host == NULL)
                   return NULL;
   
           /* Allocate memory for block, and initialize arguments */
           if (!(block = (struct nlm_block *) kmalloc(sizeof(*block), GFP_KERNEL)))
                   goto failed;
           memset(block, 0, sizeof(*block));
           locks_init_lock(&block->b_call.a_args.lock.fl);
           locks_init_lock(&block->b_call.a_res.lock.fl);
   
           if (!nlmclnt_setgrantargs(&block->b_call, lock))
                   goto failed_free;
   
           /* Set notifier function for VFS, and init args */
           block->b_call.a_args.lock.fl.fl_notify = nlmsvc_notify_blocked;
           block->b_call.a_args.cookie = *cookie;  /* see above */
   
           dprintk("lockd: created block %p...\n", block);
   
           /* Create and initialize the block */
           block->b_daemon = rqstp->rq_server;
           block->b_host   = host;
           block->b_file   = file;
   
           /* Add to file's list of blocks */
           block->b_fnext  = file->f_blocks;
           file->f_blocks  = block;
   
           /* Set up RPC arguments for callback */
           call = &block->b_call;
           call->a_host    = host;
           call->a_flags   = RPC_TASK_ASYNC;
   
           return block;
   
   failed_free:
           kfree(block);
   failed:
           nlm_release_host(host);
           return NULL;
   }
   
   /*
    * Delete a block. If the lock was cancelled or the grant callback
    * failed, unlock is set to 1.
    * It is the caller's responsibility to check whether the file
    * can be closed hereafter.
    */
   static void
   nlmsvc_delete_block(struct nlm_block *block, int unlock)
   {
           struct file_lock        *fl = &block->b_call.a_args.lock.fl;
           struct nlm_file         *file = block->b_file;
           struct nlm_block        **bp;
   
           dprintk("lockd: deleting block %p...\n", block);
   
           /* Remove block from list */
           nlmsvc_remove_block(block);
   
           /* If granted, unlock it, else remove from inode block list */
           if (unlock && block->b_granted) {
                   dprintk("lockd: deleting granted lock\n");
                   fl->fl_type = F_UNLCK;
                   posix_lock_file(&block->b_file->f_file, fl, 0);
                   block->b_granted = 0;
           } else {
                   dprintk("lockd: unblocking blocked lock\n");
                   posix_unblock_lock(fl);
           }
   
           /* If the block is in the middle of a GRANT callback,
            * don't kill it yet. */
           if (block->b_incall) {
                   nlmsvc_insert_block(block, NLM_NEVER);
                   block->b_done = 1;
                   return;
           }
   
           /* Remove block from file's list of blocks */
           for (bp = &file->f_blocks; *bp; bp = &(*bp)->b_fnext) {
                   if (*bp == block) {
                           *bp = block->b_fnext;
                           break;
                   }
           }
   
           if (block->b_host)
                   nlm_release_host(block->b_host);
           nlmclnt_freegrantargs(&block->b_call);
           kfree(block);
   }
   
   /*
    * Loop over all blocks and perform the action specified.
    * (NLM_ACT_CHECK handled by nlmsvc_inspect_file).
    */
   int
   nlmsvc_traverse_blocks(struct nlm_host *host, struct nlm_file *file, int action)
   {
           struct nlm_block        *block, *next;
   
           down(&file->f_sema);
           for (block = file->f_blocks; block; block = next) {
                   next = block->b_fnext;
                   if (action == NLM_ACT_MARK)
                           block->b_host->h_inuse = 1;
                   else if (action == NLM_ACT_UNLOCK) {
                           if (host == NULL || host == block->b_host)
                                   nlmsvc_delete_block(block, 1);
                   }
           }
           up(&file->f_sema);
           return 0;
   }
   
   /*
    * Attempt to establish a lock, and if it can't be granted, block it
    * if required.
    */
   u32
   nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
                           struct nlm_lock *lock, int wait, struct nlm_cookie *cookie)
   {
           struct file_lock        *conflock;
           struct nlm_block        *block;
           int                     error;
   
           dprintk("lockd: nlmsvc_lock(%04x/%ld, ty=%d, pi=%d, %Ld-%Ld, bl=%d)\n",
                                   file->f_file.f_dentry->d_inode->i_dev,
                                   file->f_file.f_dentry->d_inode->i_ino,
                                   lock->fl.fl_type, lock->fl.fl_pid,
                                   (long long)lock->fl.fl_start,
                                   (long long)lock->fl.fl_end,
                                   wait);
   
           /* Lock file against concurrent access */
           down(&file->f_sema);
   
           /* Get existing block (in case client is busy-waiting) */
           block = nlmsvc_lookup_block(file, lock, 0);
   
           lock->fl.fl_flags |= FL_LOCKD;
   
   again:
           if (!(conflock = posix_test_lock(&file->f_file, &lock->fl))) {
                   error = posix_lock_file(&file->f_file, &lock->fl, 0);
   
                   if (block)
                           nlmsvc_delete_block(block, 0);
                   up(&file->f_sema);
   
                   dprintk("lockd: posix_lock_file returned %d\n", -error);
                   switch(-error) {
                   case 0:
                           return nlm_granted;
                   case EDEADLK:
                           return nlm_deadlock;
                   case EAGAIN:
                           return nlm_lck_denied;
                   default:                        /* includes ENOLCK */
                           return nlm_lck_denied_nolocks;
                   }
           }
   
           if (!wait) {
                   up(&file->f_sema);
                   return nlm_lck_denied;
           }
   
           if (posix_locks_deadlock(&lock->fl, conflock)) {
                   up(&file->f_sema);
                   return nlm_deadlock;
           }
   
           /* If we don't have a block, create and initialize it. Then
            * retry because we may have slept in kmalloc. */
           if (block == NULL) {
                   dprintk("lockd: blocking on this lock (allocating).\n");
                   if (!(block = nlmsvc_create_block(rqstp, file, lock, cookie)))
                           return nlm_lck_denied_nolocks;
                   goto again;
           }
   
           /* Append to list of blocked */
           nlmsvc_insert_block(block, NLM_NEVER);
   
           if (list_empty(&block->b_call.a_args.lock.fl.fl_block)) {
                   /* Now add block to block list of the conflicting lock
                      if we haven't done so. */
                   dprintk("lockd: blocking on this lock.\n");
                   posix_block_lock(conflock, &block->b_call.a_args.lock.fl);
           }
   
           up(&file->f_sema);
           return nlm_lck_blocked;
   }
   
   /*
    * Test for presence of a conflicting lock.
    */
   u32
   nlmsvc_testlock(struct nlm_file *file, struct nlm_lock *lock,
                                          struct nlm_lock *conflock)
   {
           struct file_lock        *fl;
   
           dprintk("lockd: nlmsvc_testlock(%04x/%ld, ty=%d, %Ld-%Ld)\n",
                                   file->f_file.f_dentry->d_inode->i_dev,
                                   file->f_file.f_dentry->d_inode->i_ino,
                                   lock->fl.fl_type,
                                   (long long)lock->fl.fl_start,
                                   (long long)lock->fl.fl_end);
   
           if ((fl = posix_test_lock(&file->f_file, &lock->fl)) != NULL) {
                   dprintk("lockd: conflicting lock(ty=%d, %Ld-%Ld)\n",
                                   fl->fl_type, (long long)fl->fl_start,
                                   (long long)fl->fl_end);
                   conflock->caller = "somehost";  /* FIXME */
                   conflock->oh.len = 0;           /* don't return OH info */
                   conflock->fl = *fl;
                   return nlm_lck_denied;
           }
   
           return nlm_granted;
   }
   
   /*
    * Remove a lock.
    * This implies a CANCEL call: We send a GRANT_MSG, the client replies
    * with a GRANT_RES call which gets lost, and calls UNLOCK immediately
    * afterwards. In this case the block will still be there, and hence
    * must be removed.
    */
   u32
   nlmsvc_unlock(struct nlm_file *file, struct nlm_lock *lock)
   {
           int     error;
   
           dprintk("lockd: nlmsvc_unlock(%04x/%ld, pi=%d, %Ld-%Ld)\n",
                                   file->f_file.f_dentry->d_inode->i_dev,
                                   file->f_file.f_dentry->d_inode->i_ino,
                                   lock->fl.fl_pid,
                                   (long long)lock->fl.fl_start,
                                   (long long)lock->fl.fl_end);
   
           /* First, cancel any lock that might be there */
           nlmsvc_cancel_blocked(file, lock);
   
           lock->fl.fl_type = F_UNLCK;
           error = posix_lock_file(&file->f_file, &lock->fl, 0);
   
           return (error < 0)? nlm_lck_denied_nolocks : nlm_granted;
   }
   
   /*
    * Cancel a previously blocked request.
    *
    * A cancel request always overrides any grant that may currently
    * be in progress.
    * The calling procedure must check whether the file can be closed.
    */
   u32
   nlmsvc_cancel_blocked(struct nlm_file *file, struct nlm_lock *lock)
   {
           struct nlm_block        *block;
   
           dprintk("lockd: nlmsvc_cancel(%04x/%ld, pi=%d, %Ld-%Ld)\n",
                                   file->f_file.f_dentry->d_inode->i_dev,
                                   file->f_file.f_dentry->d_inode->i_ino,
                                   lock->fl.fl_pid,
                                   (long long)lock->fl.fl_start,
                                   (long long)lock->fl.fl_end);
   
           down(&file->f_sema);
           if ((block = nlmsvc_lookup_block(file, lock, 1)) != NULL)
                   nlmsvc_delete_block(block, 1);
           up(&file->f_sema);
           return nlm_granted;
   }
   
   /*
    * Unblock a blocked lock request. This is a callback invoked from the
    * VFS layer when a lock on which we blocked is removed.
    *
    * This function doesn't grant the blocked lock instantly, but rather moves
    * the block to the head of nlm_blocked where it can be picked up by lockd.
    */
   static void
   nlmsvc_notify_blocked(struct file_lock *fl)
   {
           struct nlm_block        **bp, *block;
   
           dprintk("lockd: VFS unblock notification for block %p\n", fl);
           posix_unblock_lock(fl);
           for (bp = &nlm_blocked; (block = *bp); bp = &block->b_next) {
                   if (nlm_compare_locks(&block->b_call.a_args.lock.fl, fl)) {
                           nlmsvc_insert_block(block, 0);
                           svc_wake_up(block->b_daemon);
                           return;
                   }
           }
   
           printk(KERN_WARNING "lockd: notification for unknown block!\n");
   }
   
   /*
    * Try to claim a lock that was previously blocked.
    *
    * Note that we use both the RPC_GRANTED_MSG call _and_ an async
    * RPC thread when notifying the client. This seems like overkill...
    * Here's why:
    *  -   we don't want to use a synchronous RPC thread, otherwise
    *      we might find ourselves hanging on a dead portmapper.
    *  -   Some lockd implementations (e.g. HP) don't react to
    *      RPC_GRANTED calls; they seem to insist on RPC_GRANTED_MSG calls.
    */
   static void
   nlmsvc_grant_blocked(struct nlm_block *block)
   {
           struct nlm_file         *file = block->b_file;
           struct nlm_lock         *lock = &block->b_call.a_args.lock;
           struct file_lock        *conflock;
           int                     error;
   
           dprintk("lockd: grant blocked lock %p\n", block);
   
           /* First thing is lock the file */
           down(&file->f_sema);
   
           /* Unlink block request from list */
           nlmsvc_remove_block(block);
   
           /* If b_granted is true this means we've been here before.
            * Just retry the grant callback, possibly refreshing the RPC
            * binding */
           if (block->b_granted) {
                   nlm_rebind_host(block->b_host);
                   goto callback;
           }
   
           /* Try the lock operation again */
           if ((conflock = posix_test_lock(&file->f_file, &lock->fl)) != NULL) {
                   /* Bummer, we blocked again */
                   dprintk("lockd: lock still blocked\n");
                   nlmsvc_insert_block(block, NLM_NEVER);
                   posix_block_lock(conflock, &lock->fl);
                   up(&file->f_sema);
                   return;
           }
   
           /* Alright, no conflicting lock. Now lock it for real. If the
            * following yields an error, this is most probably due to low
            * memory. Retry the lock in a few seconds.
            */
           if ((error = posix_lock_file(&file->f_file, &lock->fl, 0)) < 0) {
                   printk(KERN_WARNING "lockd: unexpected error %d in %s!\n",
                                   -error, __FUNCTION__);
                   nlmsvc_insert_block(block, 10 * HZ);
                   up(&file->f_sema);
                   return;
           }
   
   callback:
           /* Lock was granted by VFS. */
           dprintk("lockd: GRANTing blocked lock.\n");
           block->b_granted = 1;
           block->b_incall  = 1;
   
           /* Schedule next grant callback in 30 seconds */
           nlmsvc_insert_block(block, 30 * HZ);
   
           /* Call the client */
           nlm_get_host(block->b_call.a_host);
           if (nlmsvc_async_call(&block->b_call, NLMPROC_GRANTED_MSG,
                                                   nlmsvc_grant_callback) < 0)
                   nlm_release_host(block->b_call.a_host);
           up(&file->f_sema);
   }
   
   /*
    * This is the callback from the RPC layer when the NLM_GRANTED_MSG
    * RPC call has succeeded or timed out.
    * Like all RPC callbacks, it is invoked by the rpciod process, so it
    * better not sleep. Therefore, we put the blocked lock on the nlm_blocked
    * chain once more in order to have it removed by lockd itself (which can
    * then sleep on the file semaphore without disrupting e.g. the nfs client).
    */
   static void
   nlmsvc_grant_callback(struct rpc_task *task)
   {
           struct nlm_rqst         *call = (struct nlm_rqst *) task->tk_calldata;
           struct nlm_block        *block;
           unsigned long           timeout;
   
           dprintk("lockd: GRANT_MSG RPC callback\n");
           dprintk("callback: looking for cookie %x \n", 
                   *(unsigned int *)(call->a_args.cookie.data));
           if (!(block = nlmsvc_find_block(&call->a_args.cookie))) {
                   dprintk("lockd: no block for cookie %x\n", *(u32 *)(call->a_args.cookie.data));
                   return;
           }
   
           /* Technically, we should down the file semaphore here. Since we
            * move the block towards the head of the queue only, no harm
            * can be done, though. */
           if (task->tk_status < 0) {
                   /* RPC error: Re-insert for retransmission */
                   timeout = 10 * HZ;
           } else if (block->b_done) {
                   /* Block already removed, kill it for real */
                   timeout = 0;
           } else {
                   /* Call was successful, now wait for client callback */
                   timeout = 60 * HZ;
           }
           nlmsvc_insert_block(block, timeout);
           svc_wake_up(block->b_daemon);
           block->b_incall = 0;
   
           nlm_release_host(call->a_host);
   }
   
   /*
    * We received a GRANT_RES callback. Try to find the corresponding
    * block.
    */
   void
   nlmsvc_grant_reply(struct nlm_cookie *cookie, u32 status)
   {
           struct nlm_block        *block;
           struct nlm_file         *file;
   
           if (!(block = nlmsvc_find_block(cookie)))
                   return;
           file = block->b_file;
   
           file->f_count++;
           down(&file->f_sema);
           if ((block = nlmsvc_find_block(cookie)) != NULL) {
                   if (status == NLM_LCK_DENIED_GRACE_PERIOD) {
                           /* Try again in a couple of seconds */
                           nlmsvc_insert_block(block, 10 * HZ);
                           block = NULL;
                   } else {
                           /* Lock is now held by client, or has been rejected.
                            * In both cases, the block should be removed. */
                           file->f_count++;
                           up(&file->f_sema);
                           if (status == NLM_LCK_GRANTED)
                                   nlmsvc_delete_block(block, 0);
                           else
                                   nlmsvc_delete_block(block, 1);
                   }
           }
           if (!block)
                   up(&file->f_sema);
           nlm_release_file(file);
   }
   
   /*
    * Retry all blocked locks that have been notified. This is where lockd
    * picks up locks that can be granted, or grant notifications that must
    * be retransmitted.
    */
   unsigned long
   nlmsvc_retry_blocked(void)
   {
           struct nlm_block        *block;
   
           dprintk("nlmsvc_retry_blocked(%p, when=%ld)\n",
                           nlm_blocked,
                           nlm_blocked? nlm_blocked->b_when : 0);
           while ((block = nlm_blocked)) {
                   if (block->b_when == NLM_NEVER)
                           break;
                   if (time_after(block->b_when,jiffies))
                           break;
                   dprintk("nlmsvc_retry_blocked(%p, when=%ld, done=%d)\n",
                           block, block->b_when, block->b_done);
                   if (block->b_done)
                           nlmsvc_delete_block(block, 0);
                   else
                           nlmsvc_grant_blocked(block);
           }
   
           if ((block = nlm_blocked) && block->b_when != NLM_NEVER)
                   return (block->b_when - jiffies);
   
           return MAX_SCHEDULE_TIMEOUT;
   }

Cache object: 793877bcc81e7e18b501f012f2b7ec69