From: Valerie Aurora <val@xxxxxxxxxxxxxxxxx> File system freeze/thaw require the superblock's s_umount lock. However, we write to the file system while holding the s_umount lock in several places (e.g., writeback and quotas). Any of these can block on a frozen file system while holding s_umount, preventing any later thaw from occurring, since thaw requires s_umount. The solution is to add a check, vfs_is_frozen(), to all code paths that write while holding sb->s_umount and return without writing if it is true. BugLink: https://bugs.launchpad.net/bugs/897421 Signed-off-by: Valerie Aurora <val@xxxxxxxxxxxxxxxxx> Cc: Kamal Mostafa <kamal@xxxxxxxxxxxxx> Tested-by: Peter M. Petrakis <peter.petrakis@xxxxxxxxxxxxx> [kamal@xxxxxxxxxxxxx: minor changes; patch restructure] Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx> --- fs/fs-writeback.c | 8 ++++++++ fs/quota/quota.c | 21 ++++++++++++++++++++- fs/super.c | 8 ++++++++ fs/sync.c | 4 ++-- include/linux/fs.h | 7 ++++++- 5 files changed, 44 insertions(+), 4 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 73c3992..eee01cd 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -554,6 +554,14 @@ static long writeback_sb_inodes(struct super_block *sb, while (!list_empty(&wb->b_io)) { struct inode *inode = wb_inode(wb->b_io.prev); + if (inode->i_sb == sb && vfs_is_frozen(sb)) { + /* + * Inode is on a frozen superblock; skip it for now. + */ + redirty_tail(inode, wb); + continue; + } + if (inode->i_sb != sb) { if (work->sb) { /* diff --git a/fs/quota/quota.c b/fs/quota/quota.c index 35f4b0e..1d770f2 100644 --- a/fs/quota/quota.c +++ b/fs/quota/quota.c @@ -47,7 +47,7 @@ static int check_quotactl_permission(struct super_block *sb, int type, int cmd, static void quota_sync_one(struct super_block *sb, void *arg) { - if (sb->s_qcop && sb->s_qcop->quota_sync) + if (sb->s_qcop && sb->s_qcop->quota_sync && !vfs_is_frozen(sb)) sb->s_qcop->quota_sync(sb, *(int *)arg, 1); } @@ -368,8 +368,27 @@ SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special, goto out; } + /* + * If the fs is frozen, only allow read-only quota subcmds. + */ + if (vfs_is_frozen(sb)) { + switch (cmd) { + case Q_GETFMT: + case Q_GETINFO: + case Q_XGETQSTAT: + ret = 0; + break; + default: + ret = -EBUSY; + break; + } + if ( ret != 0 ) + goto out_drop_super; + } + ret = do_quotactl(sb, type, cmds, id, addr, pathp); +out_drop_super: drop_super(sb); out: if (pathp && !IS_ERR(pathp)) diff --git a/fs/super.c b/fs/super.c index afd0f1a..5629d06 100644 --- a/fs/super.c +++ b/fs/super.c @@ -526,6 +526,10 @@ void sync_supers(void) * * Scans the superblock list and calls given function, passing it * locked superblock and given argument. + * + * Note: If @f is going to write to the file system, it must first + * check if the file system is frozen (via vfs_is_frozen(sb)) and + * refuse to write if so. */ void iterate_supers(void (*f)(struct super_block *, void *), void *arg) { @@ -595,6 +599,10 @@ EXPORT_SYMBOL(iterate_supers_type); * * Scans the superblock list and finds the superblock of the file system * mounted on the device given. %NULL is returned if no match is found. + * + * Note: If caller is going to write to the superblock, it must first + * check if the file system is frozen (via vfs_is_frozen(sb)) and + * refuse to write if so. */ struct super_block *get_super(struct block_device *bdev) diff --git a/fs/sync.c b/fs/sync.c index 101b8ef..e8166db 100644 --- a/fs/sync.c +++ b/fs/sync.c @@ -68,7 +68,7 @@ int sync_filesystem(struct super_block *sb) /* * No point in syncing out anything if the filesystem is read-only. */ - if (sb->s_flags & MS_RDONLY) + if ((sb->s_flags & MS_RDONLY) || vfs_is_frozen(sb)) return 0; ret = __sync_filesystem(sb, 0); @@ -80,7 +80,7 @@ EXPORT_SYMBOL_GPL(sync_filesystem); static void sync_one_sb(struct super_block *sb, void *arg) { - if (!(sb->s_flags & MS_RDONLY)) + if (!(sb->s_flags & MS_RDONLY) && !vfs_is_frozen(sb)) __sync_filesystem(sb, *(int *)arg); } /* diff --git a/include/linux/fs.h b/include/linux/fs.h index 019dc55..ec33b4c 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1490,7 +1490,7 @@ extern void prune_dcache_sb(struct super_block *sb, int nr_to_scan); extern struct timespec current_fs_time(struct super_block *sb); /* - * Snapshotting support. + * Snapshotting support. See freeze_super() for documentation. */ enum { SB_UNFROZEN = 0, @@ -1501,6 +1501,11 @@ enum { #define vfs_check_frozen(sb, level) \ wait_event((sb)->s_wait_unfrozen, ((sb)->s_frozen < (level))) +static inline int vfs_is_frozen(struct super_block *sb) +{ + return sb->s_frozen == SB_FREEZE_TRANS; +} + /* * until VFS tracks user namespaces for inodes, just make all files * belong to init_user_ns -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
