| Message ID | 20160901012114.6476.57874.stgit@pluto.themaw.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, 01 Sep 2016 03:21:14 +0200, Ian Kent wrote: > > Somewhere along the way the autofs expire operation has changed to > hold a spin lock over expired dentry selection. The autofs indirect > mount expired dentry selection is complicated and quite lengthy so > it isn't appropriate to hold a spin lock over the operation. > > Commit 47be6184 added a might_sleep() to dput() causing a BUG() > about this usage to be issued. > > But the spin lock doesn't need to be held over this check, the > autofs dentry info. flags are enough to block walks into dentrys > during the expire. > > I've left the direct mount expire as it is (for now) becuase it > is much simpler and quicker than the indirect mount expire and > adding spin lock release and re-aquires would do nothing more > than add overhead. > > Signed-off-by: Ian Kent <raven@themaw.net> Looks working fine, so far. Reported-and-tested-by: Takashi Iwai <tiwai@suse.de> thanks, Takashi -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Sep 01 2016, Ian Kent wrote: > Somewhere along the way the autofs expire operation has changed to > hold a spin lock over expired dentry selection. The autofs indirect > mount expired dentry selection is complicated and quite lengthy so > it isn't appropriate to hold a spin lock over the operation. > > Commit 47be6184 added a might_sleep() to dput() causing a BUG() > about this usage to be issued. > > But the spin lock doesn't need to be held over this check, the > autofs dentry info. flags are enough to block walks into dentrys > during the expire. > > I've left the direct mount expire as it is (for now) becuase it > is much simpler and quicker than the indirect mount expire and > adding spin lock release and re-aquires would do nothing more > than add overhead. > > Signed-off-by: Ian Kent <raven@themaw.net> > --- > fs/autofs4/expire.c | 55 +++++++++++++++++++++++++++++++++++++++------------ > 1 file changed, 42 insertions(+), 13 deletions(-) > > diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c > index b493909..2d8e176 100644 > --- a/fs/autofs4/expire.c > +++ b/fs/autofs4/expire.c > @@ -417,6 +417,7 @@ static struct dentry *should_expire(struct dentry *dentry, > } > return NULL; > } > + > /* > * Find an eligible tree to time-out > * A tree is eligible if :- > @@ -432,6 +433,7 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb, > struct dentry *root = sb->s_root; > struct dentry *dentry; > struct dentry *expired; > + struct dentry *found; > struct autofs_info *ino; > > if (!root) > @@ -442,31 +444,46 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb, > > dentry = NULL; > while ((dentry = get_next_positive_subdir(dentry, root))) { > + int flags = how; > + > spin_lock(&sbi->fs_lock); > ino = autofs4_dentry_ino(dentry); > - if (ino->flags & AUTOFS_INF_WANT_EXPIRE) > - expired = NULL; > - else > - expired = should_expire(dentry, mnt, timeout, how); > - if (!expired) { > + if (ino->flags & AUTOFS_INF_WANT_EXPIRE) { > spin_unlock(&sbi->fs_lock); > continue; > } > + spin_unlock(&sbi->fs_lock); > + > + expired = should_expire(dentry, mnt, timeout, flags); > + if (!expired) > + continue; > + > + spin_lock(&sbi->fs_lock); > ino = autofs4_dentry_ino(expired); > ino->flags |= AUTOFS_INF_WANT_EXPIRE; > spin_unlock(&sbi->fs_lock); > synchronize_rcu(); > - spin_lock(&sbi->fs_lock); > - if (should_expire(expired, mnt, timeout, how)) { > - if (expired != dentry) > - dput(dentry); > - goto found; > - } > > + /* Make sure a reference is not taken on found if > + * things have changed. > + */ > + flags &= ~AUTOFS_EXP_LEAVES; > + found = should_expire(expired, mnt, timeout, how); > + if (!found || found != expired) > + /* Something has changed, continue */ > + goto next; > + > + if (expired != dentry) > + dput(dentry); > + > + spin_lock(&sbi->fs_lock); > + goto found; > +next: > + spin_lock(&sbi->fs_lock); > ino->flags &= ~AUTOFS_INF_WANT_EXPIRE; > + spin_unlock(&sbi->fs_lock); > if (expired != dentry) > dput(expired); > - spin_unlock(&sbi->fs_lock); > } > return NULL; > > @@ -483,6 +500,7 @@ int autofs4_expire_wait(struct dentry *dentry, int rcu_walk) > struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb); > struct autofs_info *ino = autofs4_dentry_ino(dentry); > int status; > + int state; > > /* Block on any pending expire */ > if (!(ino->flags & AUTOFS_INF_WANT_EXPIRE)) > @@ -490,8 +508,19 @@ int autofs4_expire_wait(struct dentry *dentry, int rcu_walk) > if (rcu_walk) > return -ECHILD; > > +retry: > spin_lock(&sbi->fs_lock); > - if (ino->flags & AUTOFS_INF_EXPIRING) { > + state = ino->flags & (AUTOFS_INF_WANT_EXPIRE | AUTOFS_INF_EXPIRING); > + if (state == AUTOFS_INF_WANT_EXPIRE) { > + spin_unlock(&sbi->fs_lock); > + /* > + * Possibly being selected for expire, wait until > + * it's selected or not. > + */ > + schedule_timeout(HZ/10); Hi Ian, I think you want schedule_timeout_uninterruptible(HZ/10) here. schedule_timeout() only causes a delay if the task state has been changed from runnable. There is a similar bug in fscache_object_sleep_till_congested(). Nothing changes the task state from TASK_RUNNING in that function before it calls schedule_timeout(*timeoutp); Also should this patch be marked as Fixes: 47be61845c77 ("fs/dcache.c: avoid soft-lockup in dput()") so it follows that patch in -stable backport? Thanks, NeilBrown
On Fri, 2016-09-09 at 11:39 +1000, NeilBrown wrote: > On Thu, Sep 01 2016, Ian Kent wrote: > > > Somewhere along the way the autofs expire operation has changed to > > hold a spin lock over expired dentry selection. The autofs indirect > > mount expired dentry selection is complicated and quite lengthy so > > it isn't appropriate to hold a spin lock over the operation. > > > > Commit 47be6184 added a might_sleep() to dput() causing a BUG() > > about this usage to be issued. > > > > But the spin lock doesn't need to be held over this check, the > > autofs dentry info. flags are enough to block walks into dentrys > > during the expire. > > > > I've left the direct mount expire as it is (for now) becuase it > > is much simpler and quicker than the indirect mount expire and > > adding spin lock release and re-aquires would do nothing more > > than add overhead. > > > > Signed-off-by: Ian Kent <raven@themaw.net> > > --- > > fs/autofs4/expire.c | 55 +++++++++++++++++++++++++++++++++++++++--------- > > --- > > 1 file changed, 42 insertions(+), 13 deletions(-) > > > > diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c > > index b493909..2d8e176 100644 > > --- a/fs/autofs4/expire.c > > +++ b/fs/autofs4/expire.c > > @@ -417,6 +417,7 @@ static struct dentry *should_expire(struct dentry > > *dentry, > > } > > return NULL; > > } > > + > > /* > > * Find an eligible tree to time-out > > * A tree is eligible if :- > > @@ -432,6 +433,7 @@ struct dentry *autofs4_expire_indirect(struct > > super_block *sb, > > struct dentry *root = sb->s_root; > > struct dentry *dentry; > > struct dentry *expired; > > + struct dentry *found; > > struct autofs_info *ino; > > > > if (!root) > > @@ -442,31 +444,46 @@ struct dentry *autofs4_expire_indirect(struct > > super_block *sb, > > > > dentry = NULL; > > while ((dentry = get_next_positive_subdir(dentry, root))) { > > + int flags = how; > > + > > spin_lock(&sbi->fs_lock); > > ino = autofs4_dentry_ino(dentry); > > - if (ino->flags & AUTOFS_INF_WANT_EXPIRE) > > - expired = NULL; > > - else > > - expired = should_expire(dentry, mnt, timeout, how); > > - if (!expired) { > > + if (ino->flags & AUTOFS_INF_WANT_EXPIRE) { > > spin_unlock(&sbi->fs_lock); > > continue; > > } > > + spin_unlock(&sbi->fs_lock); > > + > > + expired = should_expire(dentry, mnt, timeout, flags); > > + if (!expired) > > + continue; > > + > > + spin_lock(&sbi->fs_lock); > > ino = autofs4_dentry_ino(expired); > > ino->flags |= AUTOFS_INF_WANT_EXPIRE; > > spin_unlock(&sbi->fs_lock); > > synchronize_rcu(); > > - spin_lock(&sbi->fs_lock); > > - if (should_expire(expired, mnt, timeout, how)) { > > - if (expired != dentry) > > - dput(dentry); > > - goto found; > > - } > > > > + /* Make sure a reference is not taken on found if > > + * things have changed. > > + */ > > + flags &= ~AUTOFS_EXP_LEAVES; > > + found = should_expire(expired, mnt, timeout, how); > > + if (!found || found != expired) > > + /* Something has changed, continue */ > > + goto next; > > + > > + if (expired != dentry) > > + dput(dentry); > > + > > + spin_lock(&sbi->fs_lock); > > + goto found; > > +next: > > + spin_lock(&sbi->fs_lock); > > ino->flags &= ~AUTOFS_INF_WANT_EXPIRE; > > + spin_unlock(&sbi->fs_lock); > > if (expired != dentry) > > dput(expired); > > - spin_unlock(&sbi->fs_lock); > > } > > return NULL; > > > > @@ -483,6 +500,7 @@ int autofs4_expire_wait(struct dentry *dentry, int > > rcu_walk) > > struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb); > > struct autofs_info *ino = autofs4_dentry_ino(dentry); > > int status; > > + int state; > > > > /* Block on any pending expire */ > > if (!(ino->flags & AUTOFS_INF_WANT_EXPIRE)) > > @@ -490,8 +508,19 @@ int autofs4_expire_wait(struct dentry *dentry, int > > rcu_walk) > > if (rcu_walk) > > return -ECHILD; > > > > +retry: > > spin_lock(&sbi->fs_lock); > > - if (ino->flags & AUTOFS_INF_EXPIRING) { > > + state = ino->flags & (AUTOFS_INF_WANT_EXPIRE | > > AUTOFS_INF_EXPIRING); > > + if (state == AUTOFS_INF_WANT_EXPIRE) { > > + spin_unlock(&sbi->fs_lock); > > + /* > > + * Possibly being selected for expire, wait until > > + * it's selected or not. > > + */ > > + schedule_timeout(HZ/10); > > Hi Ian, > > I think you want schedule_timeout_uninterruptible(HZ/10) here. > schedule_timeout() only causes a delay if the task state has been > changed from runnable. Right, I'll have another look, I saw that should be used but didn't actually do the change state. I have another location that calls schedule_timeout() which likely needs the same treatment. > > There is a similar bug in fscache_object_sleep_till_congested(). > Nothing changes the task state from TASK_RUNNING in that function > before it calls schedule_timeout(*timeoutp); > > Also should this patch be marked as > > Fixes: 47be61845c77 ("fs/dcache.c: avoid soft-lockup in dput()") Indeed yes, I'll do that in a re-post, thanks. Ian -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c index b493909..2d8e176 100644 --- a/fs/autofs4/expire.c +++ b/fs/autofs4/expire.c @@ -417,6 +417,7 @@ static struct dentry *should_expire(struct dentry *dentry, } return NULL; } + /* * Find an eligible tree to time-out * A tree is eligible if :- @@ -432,6 +433,7 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb, struct dentry *root = sb->s_root; struct dentry *dentry; struct dentry *expired; + struct dentry *found; struct autofs_info *ino; if (!root) @@ -442,31 +444,46 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb, dentry = NULL; while ((dentry = get_next_positive_subdir(dentry, root))) { + int flags = how; + spin_lock(&sbi->fs_lock); ino = autofs4_dentry_ino(dentry); - if (ino->flags & AUTOFS_INF_WANT_EXPIRE) - expired = NULL; - else - expired = should_expire(dentry, mnt, timeout, how); - if (!expired) { + if (ino->flags & AUTOFS_INF_WANT_EXPIRE) { spin_unlock(&sbi->fs_lock); continue; } + spin_unlock(&sbi->fs_lock); + + expired = should_expire(dentry, mnt, timeout, flags); + if (!expired) + continue; + + spin_lock(&sbi->fs_lock); ino = autofs4_dentry_ino(expired); ino->flags |= AUTOFS_INF_WANT_EXPIRE; spin_unlock(&sbi->fs_lock); synchronize_rcu(); - spin_lock(&sbi->fs_lock); - if (should_expire(expired, mnt, timeout, how)) { - if (expired != dentry) - dput(dentry); - goto found; - } + /* Make sure a reference is not taken on found if + * things have changed. + */ + flags &= ~AUTOFS_EXP_LEAVES; + found = should_expire(expired, mnt, timeout, how); + if (!found || found != expired) + /* Something has changed, continue */ + goto next; + + if (expired != dentry) + dput(dentry); + + spin_lock(&sbi->fs_lock); + goto found; +next: + spin_lock(&sbi->fs_lock); ino->flags &= ~AUTOFS_INF_WANT_EXPIRE; + spin_unlock(&sbi->fs_lock); if (expired != dentry) dput(expired); - spin_unlock(&sbi->fs_lock); } return NULL; @@ -483,6 +500,7 @@ int autofs4_expire_wait(struct dentry *dentry, int rcu_walk) struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb); struct autofs_info *ino = autofs4_dentry_ino(dentry); int status; + int state; /* Block on any pending expire */ if (!(ino->flags & AUTOFS_INF_WANT_EXPIRE)) @@ -490,8 +508,19 @@ int autofs4_expire_wait(struct dentry *dentry, int rcu_walk) if (rcu_walk) return -ECHILD; +retry: spin_lock(&sbi->fs_lock); - if (ino->flags & AUTOFS_INF_EXPIRING) { + state = ino->flags & (AUTOFS_INF_WANT_EXPIRE | AUTOFS_INF_EXPIRING); + if (state == AUTOFS_INF_WANT_EXPIRE) { + spin_unlock(&sbi->fs_lock); + /* + * Possibly being selected for expire, wait until + * it's selected or not. + */ + schedule_timeout(HZ/10); + goto retry; + } + if (state & AUTOFS_INF_EXPIRING) { spin_unlock(&sbi->fs_lock); pr_debug("waiting for expire %p name=%pd\n", dentry, dentry);
Somewhere along the way the autofs expire operation has changed to hold a spin lock over expired dentry selection. The autofs indirect mount expired dentry selection is complicated and quite lengthy so it isn't appropriate to hold a spin lock over the operation. Commit 47be6184 added a might_sleep() to dput() causing a BUG() about this usage to be issued. But the spin lock doesn't need to be held over this check, the autofs dentry info. flags are enough to block walks into dentrys during the expire. I've left the direct mount expire as it is (for now) becuase it is much simpler and quicker than the indirect mount expire and adding spin lock release and re-aquires would do nothing more than add overhead. Signed-off-by: Ian Kent <raven@themaw.net> --- fs/autofs4/expire.c | 55 +++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 42 insertions(+), 13 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html