Commit d46b0da7 authored by Dave Wysochanski's avatar Dave Wysochanski Committed by Steve French
Browse files

cifs: Fix cifsInodeInfo lock_sem deadlock when reconnect occurs 



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: default avatarDave Wysochanski <dwysocha@redhat.com>
Suggested-by: default avatarRonnie Sahlberg <lsahlber@redhat.com>
Reviewed--by: default avatarRonnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: default avatarPavel Shilovsky <pshilov@microsoft.com>
parent 1a67c415

fs/cifs/cifsglob.h

+5 −0
Original line number Diff line number Diff line
@@ -1391,6 +1391,11 @@ void cifsFileInfo_put(struct cifsFileInfo *cifs_file); 
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 cifs_down_write() instead of down_write()

	 * for this semaphore to avoid deadlocks.

	 */

	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;

fs/cifs/cifsproto.h

+1 −0
Original line number Diff line number Diff line
@@ -170,6 +170,7 @@ extern int cifs_unlock_range(struct cifsFileInfo *cfile, 
			     struct file_lock *flock, const unsigned int xid);

extern int cifs_push_mandatory_locks(struct cifsFileInfo *cfile);



extern void cifs_down_write(struct rw_semaphore *sem);

extern struct cifsFileInfo *cifs_new_fileinfo(struct cifs_fid *fid,

					      struct file *file,

					      struct tcon_link *tlink,

fs/cifs/file.c

+15 −8
Original line number Diff line number Diff line
@@ -281,6 +281,13 @@ cifs_has_mand_locks(struct cifsInodeInfo *cinode) 
	return has_locks;

}



void

cifs_down_write(struct rw_semaphore *sem)

{

	while (!down_write_trylock(sem))

		msleep(10);

}



struct cifsFileInfo *

cifs_new_fileinfo(struct cifs_fid *fid, struct file *file,

		  struct tcon_link *tlink, __u32 oplock)
@@ -306,7 +313,7 @@ cifs_new_fileinfo(struct cifs_fid *fid, struct file *file, 
	INIT_LIST_HEAD(&fdlocks->locks);

	fdlocks->cfile = cfile;

	cfile->llist = fdlocks;

	down_write(&cinode->lock_sem);

	cifs_down_write(&cinode->lock_sem);

	list_add(&fdlocks->llist, &cinode->llist);

	up_write(&cinode->lock_sem);
@@ -464,7 +471,7 @@ 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);

	cifs_down_write(&cifsi->lock_sem);

	list_for_each_entry_safe(li, tmp, &cifs_file->llist->locks, llist) {

		list_del(&li->llist);

		cifs_del_lock_waiters(li);
@@ -1027,7 +1034,7 @@ static void 
cifs_lock_add(struct cifsFileInfo *cfile, struct cifsLockInfo *lock)

{

	struct cifsInodeInfo *cinode = CIFS_I(d_inode(cfile->dentry));

	down_write(&cinode->lock_sem);

	cifs_down_write(&cinode->lock_sem);

	list_add_tail(&lock->llist, &cfile->llist->locks);

	up_write(&cinode->lock_sem);

}
@@ -1049,7 +1056,7 @@ cifs_lock_add_if(struct cifsFileInfo *cfile, struct cifsLockInfo *lock, 


try_again:

	exist = false;

	down_write(&cinode->lock_sem);

	cifs_down_write(&cinode->lock_sem);



	exist = cifs_find_lock_conflict(cfile, lock->offset, lock->length,

					lock->type, lock->flags, &conf_lock,
@@ -1072,7 +1079,7 @@ try_again: 
					(lock->blist.next == &lock->blist));

		if (!rc)

			goto try_again;

		down_write(&cinode->lock_sem);

		cifs_down_write(&cinode->lock_sem);

		list_del_init(&lock->blist);

	}
@@ -1125,7 +1132,7 @@ cifs_posix_lock_set(struct file *file, struct file_lock *flock) 
		return rc;



try_again:

	down_write(&cinode->lock_sem);

	cifs_down_write(&cinode->lock_sem);

	if (!cinode->can_cache_brlcks) {

		up_write(&cinode->lock_sem);

		return rc;
@@ -1331,7 +1338,7 @@ cifs_push_locks(struct cifsFileInfo *cfile) 
	int rc = 0;



	/* we are going to update can_cache_brlcks here - need a write access */

	down_write(&cinode->lock_sem);

	cifs_down_write(&cinode->lock_sem);

	if (!cinode->can_cache_brlcks) {

		up_write(&cinode->lock_sem);

		return rc;
@@ -1522,7 +1529,7 @@ cifs_unlock_range(struct cifsFileInfo *cfile, struct file_lock *flock, 
	if (!buf)

		return -ENOMEM;



	down_write(&cinode->lock_sem);

	cifs_down_write(&cinode->lock_sem);

	for (i = 0; i < 2; i++) {

		cur = buf;

		num = 0;

fs/cifs/smb2file.c

+1 −1
Original line number Diff line number Diff line
@@ -145,7 +145,7 @@ smb2_unlock_range(struct cifsFileInfo *cfile, struct file_lock *flock, 


	cur = buf;



	down_write(&cinode->lock_sem);

	cifs_down_write(&cinode->lock_sem);

	list_for_each_entry_safe(li, tmp, &cfile->llist->locks, llist) {

		if (flock->fl_start > li->offset ||

		    (flock->fl_start + length) <

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