Re: [PATCH UPDATED 38/40] cifs: use workqueue instead of slow-work

Tejun Heo
2010-01-22T11:10:01Z

Workqueue can now handle high concurrency. Use system_single_wq
instead of slow-work.

* Updated is_valid_oplock_break() to not call cifs_oplock_break_put()
as advised by Steve French. It might cause deadlock. Instead,
reference is increased after queueing succeeded and
cifs_oplock_break() briefly grabs GlobalSMBSeslock before putting
the cfile to make sure it doesn't put before the matching get is
finished.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Steve French <sfrench@samba.org>
---
Another approach would be to put from a different work which would be
cleaner but need more code. How does this one look to you?

Thanks.

fs/cifs/Kconfig | 1 -
fs/cifs/cifsfs.c | 6 +-----
fs/cifs/cifsglob.h | 8 +++++---
fs/cifs/dir.c | 2 +-
fs/cifs/file.c | 30 +++++++++++++-----------------
fs/cifs/misc.c | 20 ++++++++++++--------
6 files changed, 32 insertions(+), 35 deletions(-)

Index: work/fs/cifs/cifsfs.c
===================================================================
--- work.orig/fs/cifs/cifsfs.c
+++ work/fs/cifs/cifsfs.c
@@ -1038,15 +1038,10 @@ init_cifs(void)
if (rc)
goto out_unregister_key_type;
#endif
- rc = slow_work_register_user(THIS_MODULE);
- if (rc)
- goto out_unregister_resolver_key;

return 0;

- out_unregister_resolver_key:
#ifdef CONFIG_CIFS_DFS_UPCALL
- unregister_key_type(&key_type_dns_resolver);
out_unregister_key_type:
#endif
#ifdef CONFIG_CIFS_UPCALL
@@ -1069,6 +1064,7 @@ static void __exit
exit_cifs(void)
{
cFYI(DBG2, ("exit_cifs"));
+ flush_workqueue(system_single_wq);
cifs_proc_clean();
#ifdef CONFIG_CIFS_DFS_UPCALL
cifs_dfs_release_automount_timer();
Index: work/fs/cifs/cifsglob.h
===================================================================
--- work.orig/fs/cifs/cifsglob.h
+++ work/fs/cifs/cifsglob.h
@@ -18,7 +18,7 @@
*/
#include <linux/in.h>
#include <linux/in6.h>
-#include <linux/slow-work.h>
+#include <linux/workqueue.h>
#include "cifs_fs_sb.h"
#include "cifsacl.h"
/*
@@ -356,7 +356,7 @@ struct cifsFileInfo {
atomic_t count; /* reference count */
struct mutex fh_mutex; /* prevents reopen race after dead ses*/
struct cifs_search_info srch_inf;
- struct slow_work oplock_break; /* slow_work job for oplock breaks */
+ struct work_struct oplock_break; /* work for oplock breaks */
};

/* Take a reference on the file private data */
@@ -723,4 +723,6 @@ GLOBAL_EXTERN unsigned int cifs_min_rcv;
GLOBAL_EXTERN unsigned int cifs_min_small; /* min size of small buf pool */
GLOBAL_EXTERN unsigned int cifs_max_pending; /* MAX requests at once to server*/

-extern const struct slow_work_ops cifs_oplock_break_ops;
+void cifs_oplock_break(struct work_struct *work);
+void cifs_oplock_break_get(struct cifsFileInfo *cfile);
+void cifs_oplock_break_put(struct cifsFileInfo *cfile);
Index: work/fs/cifs/dir.c
===================================================================
--- work.orig/fs/cifs/dir.c
+++ work/fs/cifs/dir.c
@@ -157,7 +157,7 @@ cifs_new_fileinfo(struct inode *newinode
mutex_init(&pCifsFile->lock_mutex);
INIT_LIST_HEAD(&pCifsFile->llist);
atomic_set(&pCifsFile->count, 1);
- slow_work_init(&pCifsFile->oplock_break, &cifs_oplock_break_ops);
+ INIT_WORK(&pCifsFile->oplock_break, cifs_oplock_break);

write_lock(&GlobalSMBSeslock);
list_add(&pCifsFile->tlist, &cifs_sb->tcon->openFileList);
Index: work/fs/cifs/file.c
===================================================================
--- work.orig/fs/cifs/file.c
+++ work/fs/cifs/file.c
@@ -2276,8 +2276,7 @@ out:
return rc;
}

-static void
-cifs_oplock_break(struct slow_work *work)
+void cifs_oplock_break(struct work_struct *work)
{
struct cifsFileInfo *cfile = container_of(work, struct cifsFileInfo,
oplock_break);
@@ -2316,33 +2315,30 @@ cifs_oplock_break(struct slow_work *work
LOCKING_ANDX_OPLOCK_RELEASE, false);
cFYI(1, ("Oplock release rc = %d", rc));
}
+
+ /*
+ * We might have kicked in before is_valid_oplock_break()
+ * finished grabbing reference for us. Make sure it's done by
+ * waiting for GlobalSMSSeslock.
+ */
+ write_lock(&GlobalSMBSeslock);
+ write_unlock(&GlobalSMBSeslock);
+
+ cifs_oplock_break_put(cfile);
}

-static int
-cifs_oplock_break_get(struct slow_work *work)
+void cifs_oplock_break_get(struct cifsFileInfo *cfile)
{
- struct cifsFileInfo *cfile = container_of(work, struct cifsFileInfo,
- oplock_break);
mntget(cfile->mnt);
cifsFileInfo_get(cfile);
- return 0;
}

-static void
-cifs_oplock_break_put(struct slow_work *work)
+void cifs_oplock_break_put(struct cifsFileInfo *cfile)
{
- struct cifsFileInfo *cfile = container_of(work, struct cifsFileInfo,
- oplock_break);
mntput(cfile->mnt);
cifsFileInfo_put(cfile);
}

-const struct slow_work_ops cifs_oplock_break_ops = {
- .get_ref = cifs_oplock_break_get,
- .put_ref = cifs_oplock_break_put,
- .execute = cifs_oplock_break,
-};
-
const struct address_space_operations cifs_addr_ops = {
.readpage = cifs_readpage,
.readpages = cifs_readpages,
Index: work/fs/cifs/misc.c
===================================================================
--- work.orig/fs/cifs/misc.c
+++ work/fs/cifs/misc.c
@@ -499,7 +499,6 @@ is_valid_oplock_break(struct smb_hdr *bu
struct cifsTconInfo *tcon;
struct cifsInodeInfo *pCifsInode;
struct cifsFileInfo *netfile;
- int rc;

cFYI(1, ("Checking for oplock break or dnotify response"));
if ((pSMB->hdr.Command == SMB_COM_NT_TRANSACT) &&
@@ -584,13 +583,18 @@ is_valid_oplock_break(struct smb_hdr *bu
pCifsInode->clientCanCacheAll = false;
if (pSMB->OplockLevel == 0)
pCifsInode->clientCanCacheRead = false;
- rc = slow_work_enqueue(&netfile->oplock_break);
- if (rc) {
- cERROR(1, ("failed to enqueue oplock "
- "break: %d\n", rc));
- } else {
- netfile->oplock_break_cancelled = false;
- }
+
+ /*
+ * cifs_oplock_break_put() can't be called
+ * from here. Get reference after queueing
+ * succeeded. cifs_oplock_break() will
+ * synchronize using GlobalSMSSeslock.
+ */
+ if (queue_work(system_single_wq,
+ &netfile->oplock_break))
+ cifs_oplock_break_get(netfile);
+ netfile->oplock_break_cancelled = false;
+
read_unlock(&GlobalSMBSeslock);
read_unlock(&cifs_tcp_ses_lock);
return true;
Index: work/fs/cifs/Kconfig
===================================================================
--- work.orig/fs/cifs/Kconfig
+++ work/fs/cifs/Kconfig
@@ -2,7 +2,6 @@ config CIFS
tristate "CIFS support (advanced network filesystem, SMBFS successor)"
depends on INET
select NLS
- select SLOW_WORK
help
This is the client VFS module for the Common Internet File System
(CIFS) protocol which is the successor to the Server Message Block