So far, loop-device partition-scanning is skipped with EBUSY if the bd_mutex cannot be locked. This might happen, if someone runs open() / close() / ioctl() in parallel to LOOP_SET_FD/LOOP_CHANGE_FD and friends.
__fput() on open files might get delayed arbitrarily, which means, blkdev_put() might get called at any point in time, locking bd_mutex and thus preventing any possible partition-rescanning in parallel. This basically requires user-space to *always* run BLKRRSCAN after LOOP_SET_FD/LOOP_CHANGE_FD as we cannot know whether someone else is about to close their FD at the same time. Fix this by running BLKRRPART without holding lo_ctl_mutex, thus, we will no longer deadlock if we lock bd_mutex. Signed-off-by: David Herrmann <[email protected]> --- block/ioctl.c | 9 ++++++--- drivers/block/loop.c | 49 ++++++++++++++++++++++++++++++------------------- include/linux/fs.h | 1 + 3 files changed, 37 insertions(+), 22 deletions(-) diff --git a/block/ioctl.c b/block/ioctl.c index 6c7bf90..01c6550 100644 --- a/block/ioctl.c +++ b/block/ioctl.c @@ -150,7 +150,7 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user } } -static int blkdev_reread_part(struct block_device *bdev) +int blkdev_reread_part(struct block_device *bdev, int skipbusy) { struct gendisk *disk = bdev->bd_disk; int res; @@ -159,12 +159,15 @@ static int blkdev_reread_part(struct block_device *bdev) return -EINVAL; if (!capable(CAP_SYS_ADMIN)) return -EACCES; - if (!mutex_trylock(&bdev->bd_mutex)) + if (!skipbusy) + mutex_lock(&bdev->bd_mutex); + else if (!mutex_trylock(&bdev->bd_mutex)) return -EBUSY; res = rescan_partitions(disk, bdev); mutex_unlock(&bdev->bd_mutex); return res; } +EXPORT_SYMBOL(blkdev_reread_part); static int blk_ioctl_discard(struct block_device *bdev, uint64_t start, uint64_t len, int secure) @@ -407,7 +410,7 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd, ret = blkpg_ioctl(bdev, (struct blkpg_ioctl_arg __user *) arg); break; case BLKRRPART: - ret = blkdev_reread_part(bdev); + ret = blkdev_reread_part(bdev, 1); break; case BLKGETSIZE: size = i_size_read(bdev->bd_inode); diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 6cb1beb..4047985 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -637,7 +637,7 @@ out: * new backing store is the same size and type as the old backing store. */ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, - unsigned int arg) + unsigned int arg, int *rrpart) { struct file *file, *old_file; struct inode *inode; @@ -676,7 +676,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, fput(old_file); if (lo->lo_flags & LO_FLAGS_PARTSCAN) - ioctl_by_bdev(bdev, BLKRRPART, 0); + *rrpart = 1; return 0; out_putf: @@ -821,7 +821,7 @@ static void loop_config_discard(struct loop_device *lo) } static int loop_set_fd(struct loop_device *lo, fmode_t mode, - struct block_device *bdev, unsigned int arg) + struct block_device *bdev, unsigned int arg, int *rrpart) { struct file *file, *f; struct inode *inode; @@ -917,7 +917,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, if (part_shift) lo->lo_flags |= LO_FLAGS_PARTSCAN; if (lo->lo_flags & LO_FLAGS_PARTSCAN) - ioctl_by_bdev(bdev, BLKRRPART, 0); + *rrpart = 1; /* Grab the block_device to prevent its destruction after we * put /dev/loopXX inode. Later in loop_clr_fd() we bdput(bdev). @@ -1064,7 +1064,8 @@ static int loop_clr_fd(struct loop_device *lo) } static int -loop_set_status(struct loop_device *lo, const struct loop_info64 *info) +loop_set_status(struct loop_device *lo, const struct loop_info64 *info, + int *rrpart) { int err; struct loop_func_table *xfer; @@ -1123,7 +1124,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info) !(lo->lo_flags & LO_FLAGS_PARTSCAN)) { lo->lo_flags |= LO_FLAGS_PARTSCAN; lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN; - ioctl_by_bdev(lo->lo_device, BLKRRPART, 0); + *rrpart = 1; } lo->lo_encrypt_key_size = info->lo_encrypt_key_size; @@ -1223,7 +1224,8 @@ loop_info64_to_old(const struct loop_info64 *info64, struct loop_info *info) } static int -loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg) +loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg, + int *rrpart) { struct loop_info info; struct loop_info64 info64; @@ -1231,17 +1233,18 @@ loop_set_status_old(struct loop_device *lo, const struct loop_info __user *arg) if (copy_from_user(&info, arg, sizeof (struct loop_info))) return -EFAULT; loop_info64_from_old(&info, &info64); - return loop_set_status(lo, &info64); + return loop_set_status(lo, &info64, rrpart); } static int -loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg) +loop_set_status64(struct loop_device *lo, const struct loop_info64 __user *arg, + int *rrpart) { struct loop_info64 info64; if (copy_from_user(&info64, arg, sizeof (struct loop_info64))) return -EFAULT; - return loop_set_status(lo, &info64); + return loop_set_status(lo, &info64, rrpart); } static int @@ -1289,15 +1292,15 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd, unsigned long arg) { struct loop_device *lo = bdev->bd_disk->private_data; - int err; + int err, rrpart = 0; mutex_lock_nested(&lo->lo_ctl_mutex, 1); switch (cmd) { case LOOP_SET_FD: - err = loop_set_fd(lo, mode, bdev, arg); + err = loop_set_fd(lo, mode, bdev, arg, &rrpart); break; case LOOP_CHANGE_FD: - err = loop_change_fd(lo, bdev, arg); + err = loop_change_fd(lo, bdev, arg, &rrpart); break; case LOOP_CLR_FD: /* loop_clr_fd would have unlocked lo_ctl_mutex on success */ @@ -1309,7 +1312,8 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, err = -EPERM; if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) err = loop_set_status_old(lo, - (struct loop_info __user *)arg); + (struct loop_info __user *)arg, + &rrpart); break; case LOOP_GET_STATUS: err = loop_get_status_old(lo, (struct loop_info __user *) arg); @@ -1318,7 +1322,8 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, err = -EPERM; if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) err = loop_set_status64(lo, - (struct loop_info64 __user *) arg); + (struct loop_info64 __user *) arg, + &rrpart); break; case LOOP_GET_STATUS64: err = loop_get_status64(lo, (struct loop_info64 __user *) arg); @@ -1334,6 +1339,9 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode, mutex_unlock(&lo->lo_ctl_mutex); out_unlocked: + if (rrpart) + blkdev_reread_part(bdev, 0); + return err; } @@ -1429,7 +1437,7 @@ loop_info64_to_compat(const struct loop_info64 *info64, static int loop_set_status_compat(struct loop_device *lo, - const struct compat_loop_info __user *arg) + const struct compat_loop_info __user *arg, int *rrpart) { struct loop_info64 info64; int ret; @@ -1437,7 +1445,7 @@ loop_set_status_compat(struct loop_device *lo, ret = loop_info64_from_compat(arg, &info64); if (ret < 0) return ret; - return loop_set_status(lo, &info64); + return loop_set_status(lo, &info64, rrpart); } static int @@ -1460,14 +1468,17 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd, unsigned long arg) { struct loop_device *lo = bdev->bd_disk->private_data; - int err; + int err, rrpart = 0; switch(cmd) { case LOOP_SET_STATUS: mutex_lock(&lo->lo_ctl_mutex); err = loop_set_status_compat( - lo, (const struct compat_loop_info __user *) arg); + lo, (const struct compat_loop_info __user *) arg, + &rrpart); mutex_unlock(&lo->lo_ctl_mutex); + if (rrpart) + blkdev_reread_part(bdev, 0); break; case LOOP_GET_STATUS: mutex_lock(&lo->lo_ctl_mutex); diff --git a/include/linux/fs.h b/include/linux/fs.h index 9ab779e..755a056 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2153,6 +2153,7 @@ extern const struct file_operations bad_sock_fops; #ifdef CONFIG_BLOCK extern int ioctl_by_bdev(struct block_device *, unsigned, unsigned long); extern int blkdev_ioctl(struct block_device *, fmode_t, unsigned, unsigned long); +extern int blkdev_reread_part(struct block_device *bdev, int skipbusy); extern long compat_blkdev_ioctl(struct file *, unsigned, unsigned long); extern int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder); extern struct block_device *blkdev_get_by_path(const char *path, fmode_t mode, -- 2.2.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
