From b221f4394312ff23550fa60624e3f38bed2a1a1e Mon Sep 17 00:00:00 2001 From: Chunwei Chen Date: Thu, 20 Jul 2023 10:30:21 -0700 Subject: [PATCH] Fix zpl_test_super race with zfs_umount We cannot call zpl_enter in zpl_test_super, because zpl_test_super is under spinlock so we can't sleep, and also because zpl_test_super is called without sb->s_umount taken, so it's possible we would race with zfs_umount and call zpl_enter on freed zfsvfs. Here's an stack trace when this happens: [ 2379.114837] VERIFY(cvp->cv_magic == CV_MAGIC) failed [ 2379.114845] PANIC at spl-condvar.c:497:__cv_broadcast() [ 2379.114854] Kernel panic - not syncing: VERIFY(cvp->cv_magic == CV_MAGIC) failed [ 2379.115012] Call Trace: [ 2379.115019] dump_stack+0x74/0x96 [ 2379.115024] panic+0x114/0x2f6 [ 2379.115035] spl_panic+0xcf/0xfc [spl] [ 2379.115477] __cv_broadcast+0x68/0xa0 [spl] [ 2379.115585] rrw_exit+0xb8/0x310 [zfs] [ 2379.115696] rrm_exit+0x4a/0x80 [zfs] [ 2379.115808] zpl_test_super+0xa9/0xd0 [zfs] [ 2379.115920] sget+0xd1/0x230 [ 2379.116033] zpl_mount+0xdc/0x230 [zfs] [ 2379.116037] legacy_get_tree+0x28/0x50 [ 2379.116039] vfs_get_tree+0x27/0xc0 [ 2379.116045] path_mount+0x2fe/0xa70 [ 2379.116048] do_mount+0x80/0xa0 [ 2379.116050] __x64_sys_mount+0x8b/0xe0 [ 2379.116052] do_syscall_64+0x35/0x50 [ 2379.116054] entry_SYSCALL_64_after_hwframe+0x61/0xc6 [ 2379.116057] RIP: 0033:0x7f9912e8b26a Reviewed-by: Brian Behlendorf Signed-off-by: Chunwei Chen Closes #15077 --- module/os/linux/zfs/zfs_vfsops.c | 1 + module/os/linux/zfs/zpl_super.c | 39 ++++++++++++++++++++------------ 2 files changed, 25 insertions(+), 15 deletions(-) diff --git a/module/os/linux/zfs/zfs_vfsops.c b/module/os/linux/zfs/zfs_vfsops.c index 6b6293b9e..87c4e6dca 100644 --- a/module/os/linux/zfs/zfs_vfsops.c +++ b/module/os/linux/zfs/zfs_vfsops.c @@ -1662,6 +1662,7 @@ zfs_umount(struct super_block *sb) } zfsvfs_free(zfsvfs); + sb->s_fs_info = NULL; return (0); } diff --git a/module/os/linux/zfs/zpl_super.c b/module/os/linux/zfs/zpl_super.c index c5c230bee..ad52a11aa 100644 --- a/module/os/linux/zfs/zpl_super.c +++ b/module/os/linux/zfs/zpl_super.c @@ -277,8 +277,6 @@ zpl_test_super(struct super_block *s, void *data) { zfsvfs_t *zfsvfs = s->s_fs_info; objset_t *os = data; - int match; - /* * If the os doesn't match the z_os in the super_block, assume it is * not a match. Matching would imply a multimount of a dataset. It is @@ -286,19 +284,7 @@ zpl_test_super(struct super_block *s, void *data) * that changes the z_os, e.g., rollback, where the match will be * missed, but in that case the user will get an EBUSY. */ - if (zfsvfs == NULL || os != zfsvfs->z_os) - return (0); - - /* - * If they do match, recheck with the lock held to prevent mounting the - * wrong dataset since z_os can be stale when the teardown lock is held. - */ - if (zpl_enter(zfsvfs, FTAG) != 0) - return (0); - match = (os == zfsvfs->z_os); - zpl_exit(zfsvfs, FTAG); - - return (match); + return (zfsvfs != NULL && os == zfsvfs->z_os); } static struct super_block * @@ -324,12 +310,35 @@ zpl_mount_impl(struct file_system_type *fs_type, int flags, zfs_mnt_t *zm) s = sget(fs_type, zpl_test_super, set_anon_super, flags, os); + /* + * Recheck with the lock held to prevent mounting the wrong dataset + * since z_os can be stale when the teardown lock is held. + * + * We can't do this in zpl_test_super in since it's under spinlock and + * also s_umount lock is not held there so it would race with + * zfs_umount and zfsvfs can be freed. + */ + if (!IS_ERR(s) && s->s_fs_info != NULL) { + zfsvfs_t *zfsvfs = s->s_fs_info; + if (zpl_enter(zfsvfs, FTAG) == 0) { + if (os != zfsvfs->z_os) + err = -SET_ERROR(EBUSY); + zpl_exit(zfsvfs, FTAG); + } else { + err = -SET_ERROR(EBUSY); + } + } dsl_dataset_long_rele(dmu_objset_ds(os), FTAG); dsl_dataset_rele(dmu_objset_ds(os), FTAG); if (IS_ERR(s)) return (ERR_CAST(s)); + if (err) { + deactivate_locked_super(s); + return (ERR_PTR(err)); + } + if (s->s_root == NULL) { err = zpl_fill_super(s, zm, flags & SB_SILENT ? 1 : 0); if (err) {