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Date: Tue, 21 Aug 2007 10:19:48 -0400
From: Peter Staubach <staubach@...hat.com>
To: Ian Kent <raven@...maw.net>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Kernel Mailing List <linux-kernel@...r.kernel.org>,
autofs mailing list <autofs@...ux.kernel.org>
Subject: Re: [PATCH] autofs4: reinstate negatitive timeout of mount fails
Ian Kent wrote:
> Hi,
>
> Due to a change to fs/dcache.c:d_lookup() in the 2.6 kernel whereby only
> hashed dentrys are returned the negative caching of mount failures
> stopped working in the autofs4 module for nobrowse mount (ie. directory
> created at mount time and removed at umount or following a mount
> failure).
>
> This patch keeps track of the dentrys from mount fails in order to be
> able check the timeout since the last fail and return the appropriate
> status. In addition the timeout value is settable at load time as a
> module option and via sysfs using the module
> parameter /sys/module/autofs4/parameters/negative_timeout.
>
> Signed-off-by: Ian Kent <raven@...maw.net>
>
> ---
> --- linux-2.6.23-rc2-mm2/fs/autofs4/init.c.negative-timeout 2007-07-09 07:32:17.000000000 +0800
> +++ linux-2.6.23-rc2-mm2/fs/autofs4/init.c 2007-08-21 15:44:34.000000000 +0800
> @@ -14,6 +14,10 @@
> #include <linux/init.h>
> #include "autofs_i.h"
>
> +unsigned int negative_timeout = AUTOFS_NEGATIVE_TIMEOUT;
> +module_param(negative_timeout, uint, S_IRUGO | S_IWUSR);
> +MODULE_PARM_DESC(negative_timeout, "Cache mount fails negatively for this many seconds");
> +
> static int autofs_get_sb(struct file_system_type *fs_type,
> int flags, const char *dev_name, void *data, struct vfsmount *mnt)
> {
> --- linux-2.6.23-rc2-mm2/fs/autofs4/inode.c.negative-timeout 2007-08-17 11:52:33.000000000 +0800
> +++ linux-2.6.23-rc2-mm2/fs/autofs4/inode.c 2007-08-21 15:44:34.000000000 +0800
> @@ -46,6 +46,7 @@ struct autofs_info *autofs4_init_ino(str
> ino->inode = NULL;
> ino->dentry = NULL;
> ino->size = 0;
> + ino->negative_timeout = negative_timeout;
>
> INIT_LIST_HEAD(&ino->rehash);
>
> @@ -98,11 +99,24 @@ void autofs4_free_ino(struct autofs_info
> static void autofs4_force_release(struct autofs_sb_info *sbi)
> {
> struct dentry *this_parent = sbi->sb->s_root;
> - struct list_head *next;
> + struct list_head *p, *next;
>
> if (!sbi->sb->s_root)
> return;
>
> + /* Cleanup the negative dentry cache */
> + spin_lock(&sbi->rehash_lock);
> + list_for_each_safe(p, next, &sbi->rehash_list) {
> + struct autofs_info *ino;
> + struct dentry *dentry;
> + ino = list_entry(p, struct autofs_info, rehash);
> + dentry = ino->dentry;
> + spin_unlock(&sbi->rehash_lock);
> + dput(ino->dentry);
>
Should this be dput(dentry);?
Thanx...
ps
> + spin_lock(&sbi->rehash_lock);
> + }
> + spin_unlock(&sbi->rehash_lock);
> +
> spin_lock(&dcache_lock);
> repeat:
> next = this_parent->d_subdirs.next;
> --- linux-2.6.23-rc2-mm2/fs/autofs4/autofs_i.h.negative-timeout 2007-08-17 11:52:33.000000000 +0800
> +++ linux-2.6.23-rc2-mm2/fs/autofs4/autofs_i.h 2007-08-21 15:44:34.000000000 +0800
> @@ -40,6 +40,14 @@
> #define DPRINTK(fmt,args...) do {} while(0)
> #endif
>
> +/*
> + * If the daemon returns a negative response (AUTOFS_IOC_FAIL) then we keep
> + * the negative response cached for up to the time given here, although
> + * the time can be shorter if the kernel throws the dcache entry away.
> + */
> +#define AUTOFS_NEGATIVE_TIMEOUT 60 /* default 1 minute */
> +extern unsigned int negative_timeout;
> +
> /* Unified info structure. This is pointed to by both the dentry and
> inode structures. Each file in the filesystem has an instance of this
> structure. It holds a reference to the dentry, so dentries are never
> @@ -52,8 +60,16 @@ struct autofs_info {
>
> int flags;
>
> + /*
> + * Two types of unhashed dentry can exist on this list.
> + * Negative dentrys from failed mounts and positive dentrys
> + * resulting from a race between expire and mount. This
> + * fact is used when looking for dentrys in the list.
> + */
> struct list_head rehash;
>
> + unsigned int negative_timeout;
> +
> struct autofs_sb_info *sbi;
> unsigned long last_used;
> atomic_t count;
> --- linux-2.6.23-rc2-mm2/fs/autofs4/root.c.negative-timeout 2007-08-17 11:53:38.000000000 +0800
> +++ linux-2.6.23-rc2-mm2/fs/autofs4/root.c 2007-08-21 15:44:34.000000000 +0800
> @@ -238,6 +238,125 @@ out:
> return dcache_readdir(file, dirent, filldir);
> }
>
> +static int autofs4_compare_dentry(struct dentry *parent, struct dentry *dentry, struct qstr *name)
> +{
> + unsigned int len = name->len;
> + unsigned int hash = name->hash;
> + const unsigned char *str = name->name;
> + struct qstr *qstr = &dentry->d_name;
> +
> + if (dentry->d_name.hash != hash)
> + return 0;
> + if (dentry->d_parent != parent)
> + return 0;
> +
> + if (qstr->len != len)
> + return 0;
> + if (memcmp(qstr->name, str, len))
> + return 0;
> +
> + return 1;
> +}
> +
> +static struct dentry *autofs4_lookup_dentry(struct autofs_sb_info *sbi, struct dentry *dentry)
> +{
> + struct dentry *parent = dentry->d_parent;
> + struct qstr *name = &dentry->d_name;
> + struct list_head *p, *head;
> +
> + head = &sbi->rehash_list;
> + list_for_each(p, head) {
> + struct autofs_info *ino;
> + struct dentry *this;
> +
> + ino = list_entry(p, struct autofs_info, rehash);
> + this = ino->dentry;
> +
> + spin_lock(&this->d_lock);
> +
> + if (!autofs4_compare_dentry(parent, this, name))
> + goto next;
> +
> + if (d_unhashed(this)) {
> + spin_unlock(&this->d_lock);
> + return this;
> + }
> +next:
> + spin_unlock(&this->d_lock);
> + }
> +
> + return NULL;
> +}
> +
> +static struct dentry *autofs4_lookup_negative(struct autofs_sb_info *sbi, struct dentry *dentry)
> +{
> + struct dentry *parent = dentry->d_parent;
> + struct qstr *name = &dentry->d_name;
> + struct list_head *p, *head;
> +
> + spin_lock(&sbi->rehash_lock);
> + head = &sbi->rehash_list;
> + list_for_each(p, head) {
> + struct autofs_info *ino;
> + struct dentry *this;
> +
> + ino = list_entry(p, struct autofs_info, rehash);
> + this = ino->dentry;
> +
> + spin_lock(&this->d_lock);
> +
> + if (this->d_inode)
> + goto next;
> +
> + if (!autofs4_compare_dentry(parent, this, name))
> + goto next;
> +
> + if (d_unhashed(this)) {
> + if (autofs4_oz_mode(sbi)) {
> + spin_unlock(&this->d_lock);
> + spin_unlock(&sbi->rehash_lock);
> + return this;
> + }
> + /*
> + * If d_time is non-zero we've had a mount fail.
> + * Check if it's time to forget about it, return
> + * fail if not.
> + */
> + if (this->d_time) {
> + struct autofs_info *p_ino;
> + unsigned long neg_timeout;
> +
> + neg_timeout = this->d_time - get_seconds();
> + if (neg_timeout <= ino->negative_timeout) {
> + spin_unlock(&this->d_lock);
> + spin_unlock(&sbi->rehash_lock);
> + return ERR_PTR(-ENOENT);
> + }
> + /* Negative cache timeout */
> + this->d_time = 0;
> + list_del_init(&ino->rehash);
> + spin_unlock(&this->d_lock);
> + spin_unlock(&sbi->rehash_lock);
> + if (atomic_dec_and_test(&ino->count)) {
> + p_ino = autofs4_dentry_ino(this->d_parent);
> + if (p_ino && this->d_parent != this)
> + atomic_dec(&p_ino->count);
> + }
> + dput(this);
> + return NULL;
> + }
> + spin_unlock(&this->d_lock);
> + spin_unlock(&sbi->rehash_lock);
> + return this;
> + }
> +next:
> + spin_unlock(&this->d_lock);
> + }
> + spin_unlock(&sbi->rehash_lock);
> +
> + return NULL;
> +}
> +
> static int try_to_fill_dentry(struct dentry *dentry, int flags)
> {
> struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);
> @@ -282,7 +401,27 @@ static int try_to_fill_dentry(struct den
>
> /* Turn this into a real negative dentry? */
> if (status == -ENOENT) {
> + if (!ino) {
> + ino = autofs4_init_ino(ino, sbi, S_IFDIR | 0555);
> + if (ino == NULL)
> + return -ENOSPC;
> + dentry->d_fsdata = ino;
> + }
> + spin_lock(&sbi->rehash_lock);
> + if (!autofs4_lookup_dentry(sbi, dentry)) {
> + struct autofs_info *p_ino;
> + ino->dentry = dget(dentry);
> + atomic_inc(&ino->count);
> + p_ino = autofs4_dentry_ino(dentry->d_parent);
> + if (p_ino && dentry->d_parent != dentry)
> + atomic_inc(&p_ino->count);
> + list_add(&ino->rehash, &sbi->rehash_list);
> + }
> + spin_unlock(&sbi->rehash_lock);
> + /* Set time at which we forget about this mount fial */
> spin_lock(&dentry->d_lock);
> + ino->negative_timeout = negative_timeout;
> + dentry->d_time = get_seconds() + negative_timeout;
> dentry->d_flags &= ~DCACHE_AUTOFS_PENDING;
> spin_unlock(&dentry->d_lock);
> return status;
> @@ -305,6 +444,11 @@ static int try_to_fill_dentry(struct den
>
> if (status) {
> spin_lock(&dentry->d_lock);
> + /* Set time at which we forget about this mount fial */
> + if (status == -ENOENT) {
> + ino->negative_timeout = negative_timeout;
> + dentry->d_time = get_seconds() + negative_timeout;
> + }
> dentry->d_flags &= ~DCACHE_AUTOFS_PENDING;
> spin_unlock(&dentry->d_lock);
> return status;
> @@ -316,6 +460,7 @@ static int try_to_fill_dentry(struct den
> ino->last_used = jiffies;
>
> spin_lock(&dentry->d_lock);
> + dentry->d_time = 0;
> dentry->d_flags &= ~DCACHE_AUTOFS_PENDING;
> spin_unlock(&dentry->d_lock);
> return status;
> @@ -339,6 +484,19 @@ static void *autofs4_follow_link(struct
> if (oz_mode || !lookup_type)
> goto done;
>
> + /* Check for cached mount fail, reset d_time if timed out */
> + spin_lock(&dentry->d_lock);
> + if (dentry->d_time) {
> + unsigned long neg_timeout = dentry->d_time - get_seconds();
> + if (neg_timeout <= ino->negative_timeout) {
> + spin_unlock(&dentry->d_lock);
> + status = -ENOENT;
> + goto out_error;
> + }
> + dentry->d_time = 0;
> + }
> + spin_unlock(&dentry->d_lock);
> +
> /* If an expire request is pending wait for it. */
> if (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
> DPRINTK("waiting for active request %p name=%.*s",
> @@ -426,9 +584,28 @@ static int autofs4_revalidate(struct den
> return status;
> }
>
> - /* Negative dentry.. invalidate if "old" */
> - if (dentry->d_inode == NULL)
> - return 0;
> + /* Check for cached mount fail, reset d_time if timed out */
> + spin_lock(&dentry->d_lock);
> + if (!dentry->d_inode || dentry->d_time) {
> + struct autofs_info *ino = autofs4_dentry_ino(dentry);
> + unsigned long neg_timeout = dentry->d_time - get_seconds();
> + /*
> + * If d_time is non-zero we've had a mount fail. Check if
> + * it's time to forget about it, return fail if not.
> + */
> + if (dentry->d_time && (neg_timeout <= ino->negative_timeout)) {
> + spin_unlock(&dentry->d_lock);
> + return 1;
> + }
> + /* Negative timeout has expired */
> + dentry->d_time = 0;
> +
> + if (!dentry->d_inode) {
> + spin_unlock(&dentry->d_lock);
> + return 0;
> + }
> + }
> + spin_unlock(&dentry->d_lock);
>
> /* Check for a non-mountpoint directory with no contents */
> spin_lock(&dcache_lock);
> @@ -497,9 +674,6 @@ static struct dentry_operations autofs4_
>
> static struct dentry *autofs4_lookup_unhashed(struct autofs_sb_info *sbi, struct dentry *parent, struct qstr *name)
> {
> - unsigned int len = name->len;
> - unsigned int hash = name->hash;
> - const unsigned char *str = name->name;
> struct list_head *p, *head;
>
> spin_lock(&dcache_lock);
> @@ -508,7 +682,6 @@ static struct dentry *autofs4_lookup_unh
> list_for_each(p, head) {
> struct autofs_info *ino;
> struct dentry *dentry;
> - struct qstr *qstr;
>
> ino = list_entry(p, struct autofs_info, rehash);
> dentry = ino->dentry;
> @@ -519,20 +692,10 @@ static struct dentry *autofs4_lookup_unh
> if (!dentry->d_inode)
> goto next;
>
> - qstr = &dentry->d_name;
> -
> - if (dentry->d_name.hash != hash)
> - goto next;
> - if (dentry->d_parent != parent)
> - goto next;
> -
> - if (qstr->len != len)
> - goto next;
> - if (memcmp(qstr->name, str, len))
> + if (!autofs4_compare_dentry(parent, dentry, name))
> goto next;
>
> if (d_unhashed(dentry)) {
> - struct autofs_info *ino = autofs4_dentry_ino(dentry);
> struct inode *inode = dentry->d_inode;
>
> list_del_init(&ino->rehash);
> @@ -568,7 +731,7 @@ next:
> static struct dentry *autofs4_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
> {
> struct autofs_sb_info *sbi;
> - struct dentry *unhashed;
> + struct dentry *unhashed, *negative = NULL;
> int oz_mode;
>
> DPRINTK("name = %.*s",
> @@ -587,6 +750,22 @@ static struct dentry *autofs4_lookup(str
> unhashed = autofs4_lookup_unhashed(sbi, dentry->d_parent, &dentry->d_name);
> if (!unhashed) {
> /*
> + * Negative caching of failed "nobrowse" autofs mounts
> + * require that we keep the unhashed, negative dentrys
> + * around so we can use them to check failure status. We
> + * use the rehash_list list in the super bloxk for this
> + * purpose. This isn't needed for "browse" or direct mounts
> + * as the dentrys are always positive so the info is always
> + * available.
> + */
> + negative = autofs4_lookup_negative(sbi, dentry);
> + if (negative) {
> + if (IS_ERR(negative))
> + return negative;
> + dentry = negative;
> + goto found;
> + }
> + /*
> * Mark the dentry incomplete but don't hash it. We do this
> * to serialize our inode creation operations (symlink and
> * mkdir) which prevents deadlock during the callback to
> @@ -599,6 +778,7 @@ static struct dentry *autofs4_lookup(str
> */
> dentry->d_op = &autofs4_root_dentry_operations;
>
> + dentry->d_time = 0;
> dentry->d_fsdata = NULL;
> d_instantiate(dentry, NULL);
> } else {
> @@ -621,7 +801,7 @@ static struct dentry *autofs4_lookup(str
> }
> dentry = unhashed;
> }
> -
> +found:
> if (!oz_mode) {
> spin_lock(&dentry->d_lock);
> dentry->d_flags |= DCACHE_AUTOFS_PENDING;
> @@ -682,7 +862,7 @@ static struct dentry *autofs4_lookup(str
> return dentry;
> }
>
> - if (unhashed)
> + if (unhashed || negative)
> return dentry;
>
> return NULL;
> @@ -779,7 +959,9 @@ static int autofs4_dir_unlink(struct ino
>
> spin_lock(&dcache_lock);
> spin_lock(&sbi->rehash_lock);
> - list_add(&ino->rehash, &sbi->rehash_list);
> + dentry->d_time = 0;
> + if (!autofs4_lookup_dentry(sbi, dentry))
> + list_add(&ino->rehash, &sbi->rehash_list);
> spin_unlock(&sbi->rehash_lock);
> spin_lock(&dentry->d_lock);
> __d_drop(dentry);
> @@ -807,7 +989,9 @@ static int autofs4_dir_rmdir(struct inod
> return -ENOTEMPTY;
> }
> spin_lock(&sbi->rehash_lock);
> - list_add(&ino->rehash, &sbi->rehash_list);
> + dentry->d_time = 0;
> + if (!autofs4_lookup_dentry(sbi, dentry))
> + list_add(&ino->rehash, &sbi->rehash_list);
> spin_unlock(&sbi->rehash_lock);
> spin_lock(&dentry->d_lock);
> __d_drop(dentry);
>
>
> -
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