From: Ian Kent Date: Thu, 24 Jul 2008 04:30:27 +0000 (-0700) Subject: autofs4: fix direct mount pending expire race X-Git-Tag: v2.6.27-rc1~625 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6e60a9ab5f5d314735467752f623072f5b75157a;p=linux-2.6 autofs4: fix direct mount pending expire race For direct and offset type mounts that are covered by another mount we cannot check the AUTOFS_INF_EXPIRING flag during a path walk which leads to lookups walking into an expiring mount while it is being expired. For example, for the direct multi-mount map entry with a couple of offsets: /race/mm1 / :/ /om1 :/ /om2 :/ an autofs trigger mount is mounted on /race/mm1 and when accessed it is over mounted and trigger mounts made for /race/mm1/om1 and /race/mm1/om2. So it isn't possible for path walks to see the expiring flag at all and they happily walk into the file system while it is expiring. When expiring these mounts follow_down() must stop at the autofs mount and all processes must block in the ->follow_link() method (except the daemon) until the expire is complete. This is done by decrementing the d_mounted field of the autofs trigger mount root dentry until the expire is completed. In ->follow_link() all processes wait on the expire and the mount following is completed for the daemon until the expire is complete. Signed-off-by: Ian Kent Cc: Jeff Moyer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h index 5d90ed3b4b..4b40cbc71e 100644 --- a/fs/autofs4/autofs_i.h +++ b/fs/autofs4/autofs_i.h @@ -52,6 +52,8 @@ struct autofs_info { int flags; + struct completion expire_complete; + struct list_head active; struct list_head expiring; @@ -69,6 +71,7 @@ struct autofs_info { }; #define AUTOFS_INF_EXPIRING (1<<0) /* dentry is in the process of expiring */ +#define AUTOFS_INF_MOUNTPOINT (1<<1) /* mountpoint status for direct expire */ struct autofs_wait_queue { wait_queue_head_t queue; diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c index 19f5bea270..705b9f057f 100644 --- a/fs/autofs4/expire.c +++ b/fs/autofs4/expire.c @@ -259,13 +259,15 @@ static struct dentry *autofs4_expire_direct(struct super_block *sb, now = jiffies; timeout = sbi->exp_timeout; - /* Lock the tree as we must expire as a whole */ spin_lock(&sbi->fs_lock); if (!autofs4_direct_busy(mnt, root, timeout, do_now)) { struct autofs_info *ino = autofs4_dentry_ino(root); - - /* Set this flag early to catch sys_chdir and the like */ + if (d_mountpoint(root)) { + ino->flags |= AUTOFS_INF_MOUNTPOINT; + root->d_mounted--; + } ino->flags |= AUTOFS_INF_EXPIRING; + init_completion(&ino->expire_complete); spin_unlock(&sbi->fs_lock); return root; } @@ -392,6 +394,7 @@ found: expired, (int)expired->d_name.len, expired->d_name.name); ino = autofs4_dentry_ino(expired); ino->flags |= AUTOFS_INF_EXPIRING; + init_completion(&ino->expire_complete); spin_unlock(&sbi->fs_lock); spin_lock(&dcache_lock); list_move(&expired->d_parent->d_subdirs, &expired->d_u.d_child); @@ -429,6 +432,7 @@ int autofs4_expire_run(struct super_block *sb, spin_lock(&sbi->fs_lock); ino = autofs4_dentry_ino(dentry); ino->flags &= ~AUTOFS_INF_EXPIRING; + complete_all(&ino->expire_complete); spin_unlock(&sbi->fs_lock); return ret; @@ -457,8 +461,14 @@ int autofs4_expire_multi(struct super_block *sb, struct vfsmount *mnt, /* This is synchronous because it makes the daemon a little easier */ ret = autofs4_wait(sbi, dentry, NFY_EXPIRE); + spin_lock(&sbi->fs_lock); + if (ino->flags & AUTOFS_INF_MOUNTPOINT) { + sb->s_root->d_mounted++; + ino->flags &= ~AUTOFS_INF_MOUNTPOINT; + } ino->flags &= ~AUTOFS_INF_EXPIRING; + complete_all(&ino->expire_complete); spin_unlock(&sbi->fs_lock); dput(dentry); } diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c index 1c2579de1f..adbd8559e8 100644 --- a/fs/autofs4/root.c +++ b/fs/autofs4/root.c @@ -141,6 +141,7 @@ static int try_to_fill_dentry(struct dentry *dentry, int flags) dentry, dentry->d_name.len, dentry->d_name.name); status = autofs4_wait(sbi, dentry, NFY_NONE); + wait_for_completion(&ino->expire_complete); DPRINTK("expire done status=%d", status); @@ -227,14 +228,32 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd) DPRINTK("dentry=%p %.*s oz_mode=%d nd->flags=%d", dentry, dentry->d_name.len, dentry->d_name.name, oz_mode, nd->flags); - - /* If it's our master or we shouldn't trigger a mount we're done */ - lookup_type = nd->flags & (TRIGGER_FLAGS | TRIGGER_INTENTS); - if (oz_mode || - !(lookup_type || dentry->d_flags & DCACHE_AUTOFS_PENDING)) + /* + * For an expire of a covered direct or offset mount we need + * to beeak out of follow_down() at the autofs mount trigger + * (d_mounted--), so we can see the expiring flag, and manage + * the blocking and following here until the expire is completed. + */ + if (oz_mode) { + spin_lock(&sbi->fs_lock); + if (ino->flags & AUTOFS_INF_EXPIRING) { + spin_unlock(&sbi->fs_lock); + /* Follow down to our covering mount. */ + if (!follow_down(&nd->path.mnt, &nd->path.dentry)) + goto done; + /* + * We shouldn't need to do this but we have no way + * of knowing what may have been done so try a follow + * just in case. + */ + autofs4_follow_mount(&nd->path.mnt, &nd->path.dentry); + goto done; + } + spin_unlock(&sbi->fs_lock); goto done; + } - /* If an expire request is pending wait for it. */ + /* If an expire request is pending everyone must wait. */ spin_lock(&sbi->fs_lock); if (ino->flags & AUTOFS_INF_EXPIRING) { spin_unlock(&sbi->fs_lock); @@ -243,6 +262,7 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd) dentry, dentry->d_name.len, dentry->d_name.name); status = autofs4_wait(sbi, dentry, NFY_NONE); + wait_for_completion(&ino->expire_complete); DPRINTK("request done status=%d", status); @@ -250,10 +270,15 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd) } spin_unlock(&sbi->fs_lock); cont: + /* We trigger a mount for almost all flags */ + lookup_type = nd->flags & (TRIGGER_FLAGS | TRIGGER_INTENTS); + if (!(lookup_type || dentry->d_flags & DCACHE_AUTOFS_PENDING)) + goto done; + /* - * If the dentry contains directories then it is an - * autofs multi-mount with no root mount offset. So - * don't try to mount it again. + * If the dentry contains directories then it is an autofs + * multi-mount with no root mount offset. So don't try to + * mount it again. */ spin_lock(&dcache_lock); if (dentry->d_flags & DCACHE_AUTOFS_PENDING || @@ -264,22 +289,22 @@ cont: if (status) goto out_error; - /* - * The mount succeeded but if there is no root mount - * it must be an autofs multi-mount with no root offset - * so we don't need to follow the mount. - */ - if (d_mountpoint(dentry)) { - if (!autofs4_follow_mount(&nd->path.mnt, - &nd->path.dentry)) { - status = -ENOENT; - goto out_error; - } - } - - goto done; + goto follow; } spin_unlock(&dcache_lock); +follow: + /* + * If there is no root mount it must be an autofs + * multi-mount with no root offset so we don't need + * to follow it. + */ + if (d_mountpoint(dentry)) { + if (!autofs4_follow_mount(&nd->path.mnt, + &nd->path.dentry)) { + status = -ENOENT; + goto out_error; + } + } done: return NULL; @@ -545,6 +570,7 @@ static struct dentry *autofs4_lookup(struct inode *dir, struct dentry *dentry, s expiring, expiring->d_name.len, expiring->d_name.name); autofs4_wait(sbi, expiring, NFY_NONE); + wait_for_completion(&ino->expire_complete); DPRINTK("request completed"); goto cont; }