There's a deadlock that is possible and can easily be seen with
a test where multiple readers open/read/close of the same file
and a disruption occurs causing reconnect. The deadlock is due
a reader thread inside cifs_strict_readv calling down_read and
obtaining lock_sem, and then after reconnect inside
cifs_reopen_file calling down_read a second time. If in
between the two down_read calls, a down_write comes from
another process, deadlock occurs.
CPU0 CPU1
---- ----
cifs_strict_readv()
down_read(&cifsi->lock_sem);
_cifsFileInfo_put
OR
cifs_new_fileinfo
down_write(&cifsi->lock_sem);
cifs_reopen_file()
down_read(&cifsi->lock_sem);
Fix the above by changing all down_write(lock_sem) calls to
down_write_trylock(lock_sem)/msleep() loop, which in turn
makes the second down_read call benign since it will never
block behind the writer while holding lock_sem.
Signed-off-by: Dave Wysochanski <dwysocha@xxxxxxxxxx>
Suggested-by: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
---
fs/cifs/cifsglob.h | 5 +++++
fs/cifs/file.c | 24 ++++++++++++++++--------
fs/cifs/smb2file.c | 3 ++-
3 files changed, 23 insertions(+), 9 deletions(-)
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 50dfd9049370..2c4a7adbcb4e 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -1391,6 +1391,11 @@ struct cifs_writedata {
struct cifsInodeInfo {
bool can_cache_brlcks;
struct list_head llist; /* locks helb by this inode */
+ /*
+ * NOTE: Some code paths call down_read(lock_sem) twice, so
+ * we must always use use down_write_trylock()/msleep() loop
+ * to avoid deadlock.
+ */
struct rw_semaphore lock_sem; /* protect the fields above */
/* BB add in lists for dirty pages i.e. write caching info for oplock */
struct list_head openFileList;
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 5ad15de2bb4f..52454df5ae39 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -306,7 +306,8 @@ struct cifsFileInfo *
INIT_LIST_HEAD(&fdlocks->locks);
fdlocks->cfile = cfile;
cfile->llist = fdlocks;
- down_write(&cinode->lock_sem);
+ while (!down_write_trylock(&cinode->lock_sem))
+ msleep(125);
list_add(&fdlocks->llist, &cinode->llist);
up_write(&cinode->lock_sem);
@@ -464,7 +465,8 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
* Delete any outstanding lock records. We'll lose them when the file
* is closed anyway.
*/
- down_write(&cifsi->lock_sem);
+ while (!down_write_trylock(&cifsi->lock_sem))
+ msleep(125);
list_for_each_entry_safe(li, tmp, &cifs_file->llist->locks, llist) {
list_del(&li->llist);
cifs_del_lock_waiters(li);
@@ -1027,7 +1029,8 @@ int cifs_closedir(struct inode *inode, struct file *file)
cifs_lock_add(struct cifsFileInfo *cfile, struct cifsLockInfo *lock)
{
struct cifsInodeInfo *cinode = CIFS_I(d_inode(cfile->dentry));
- down_write(&cinode->lock_sem);
+ while (!down_write_trylock(&cinode->lock_sem))
+ msleep(125);
list_add_tail(&lock->llist, &cfile->llist->locks);
up_write(&cinode->lock_sem);
}
@@ -1049,7 +1052,8 @@ int cifs_closedir(struct inode *inode, struct file *file)
try_again:
exist = false;
- down_write(&cinode->lock_sem);
+ while (!down_write_trylock(&cinode->lock_sem))
+ msleep(125);
exist = cifs_find_lock_conflict(cfile, lock->offset, lock->length,
lock->type, lock->flags, &conf_lock,
@@ -1072,7 +1076,8 @@ int cifs_closedir(struct inode *inode, struct file *file)
(lock->blist.next == &lock->blist));
if (!rc)
goto try_again;
- down_write(&cinode->lock_sem);
+ while (!down_write_trylock(&cinode->lock_sem))
+ msleep(125);
list_del_init(&lock->blist);
}
@@ -1125,7 +1130,8 @@ int cifs_closedir(struct inode *inode, struct file *file)
return rc;
try_again:
- down_write(&cinode->lock_sem);
+ while (!down_write_trylock(&cinode->lock_sem))
+ msleep(125);
if (!cinode->can_cache_brlcks) {
up_write(&cinode->lock_sem);
return rc;
@@ -1331,7 +1337,8 @@ struct lock_to_push {
int rc = 0;
/* we are going to update can_cache_brlcks here - need a write access */
- down_write(&cinode->lock_sem);
+ while (!down_write_trylock(&cinode->lock_sem))
+ msleep(125);
if (!cinode->can_cache_brlcks) {
up_write(&cinode->lock_sem);
return rc;
@@ -1522,7 +1529,8 @@ struct lock_to_push {
if (!buf)
return -ENOMEM;
- down_write(&cinode->lock_sem);
+ while (!down_write_trylock(&cinode->lock_sem))
+ msleep(125);
for (i = 0; i < 2; i++) {
cur = buf;
num = 0;
diff --git a/fs/cifs/smb2file.c b/fs/cifs/smb2file.c
index e6a1fc72018f..61f6cc8d9cc9 100644
--- a/fs/cifs/smb2file.c
+++ b/fs/cifs/smb2file.c
@@ -145,7 +145,8 @@
cur = buf;
- down_write(&cinode->lock_sem);
+ while (!down_write_trylock(&cinode->lock_sem))
+ msleep(125);
list_for_each_entry_safe(li, tmp, &cfile->llist->locks, llist) {
if (flock->fl_start > li->offset ||
(flock->fl_start + length) <
--
1.8.3.1
