The patch titled autofs4: fix lookup deadlock has been added to the -mm tree. Its filename is autofs4-fix-lookup-deadlock.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: autofs4: fix lookup deadlock From: Ian Kent <raven@xxxxxxxxxx> A deadlock can occur when user space uses a signal (autofs version 4 uses SIGCHLD for this) to effect expire completion. The order of events is: Expire process completes, but before being able to send SIGCHLD to it's parent ... Another process walks onto a different mount point and drops the directory inode semaphore prior to sending the request to the daemon as it must ... A third process does an lstat on on the expired mount point causing it to wait on expire completion (unfortunately) holding the directory semaphore. The mount request then arrives at the daemon which does an lstat and, deadlock. For some time I was concerned about releasing the directory semaphore around the expire wait in autofs4_lookup as well as for the mount call back. I finally realized that the last round of changes in this function made the expiring dentry and the lookup dentry separate and distinct so the check and possible wait can be done anywhere prior to the mount call back. This patch moves the check to just before the mount call back and inside the directory inode mutex release. Signed-off-by: Ian Kent <raven@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/autofs4/root.c | 41 +++++++++++++++++++++-------------------- 1 file changed, 21 insertions(+), 20 deletions(-) diff -puN fs/autofs4/root.c~autofs4-fix-lookup-deadlock fs/autofs4/root.c --- a/fs/autofs4/root.c~autofs4-fix-lookup-deadlock +++ a/fs/autofs4/root.c @@ -485,22 +485,6 @@ static struct dentry *autofs4_lookup(str DPRINTK("pid = %u, pgrp = %u, catatonic = %d, oz_mode = %d", current->pid, task_pgrp_nr(current), sbi->catatonic, oz_mode); - expiring = autofs4_lookup_expiring(sbi, dentry->d_parent, &dentry->d_name); - if (expiring) { - /* - * If we are racing with expire the request might not - * be quite complete but the directory has been removed - * so it must have been successful, so just wait for it. - */ - ino = autofs4_dentry_ino(expiring); - autofs4_expire_wait(expiring); - spin_lock(&sbi->lookup_lock); - if (!list_empty(&ino->expiring)) - list_del_init(&ino->expiring); - spin_unlock(&sbi->lookup_lock); - dput(expiring); - } - unhashed = autofs4_lookup_active(sbi, dentry->d_parent, &dentry->d_name); if (unhashed) dentry = unhashed; @@ -538,14 +522,31 @@ static struct dentry *autofs4_lookup(str } if (!oz_mode) { + mutex_unlock(&dir->i_mutex); + expiring = autofs4_lookup_expiring(sbi, + dentry->d_parent, + &dentry->d_name); + if (expiring) { + /* + * If we are racing with expire the request might not + * be quite complete but the directory has been removed + * so it must have been successful, so just wait for it. + */ + ino = autofs4_dentry_ino(expiring); + autofs4_expire_wait(expiring); + spin_lock(&sbi->lookup_lock); + if (!list_empty(&ino->expiring)) + list_del_init(&ino->expiring); + spin_unlock(&sbi->lookup_lock); + dput(expiring); + } + spin_lock(&dentry->d_lock); dentry->d_flags |= DCACHE_AUTOFS_PENDING; spin_unlock(&dentry->d_lock); - if (dentry->d_op && dentry->d_op->d_revalidate) { - mutex_unlock(&dir->i_mutex); + if (dentry->d_op && dentry->d_op->d_revalidate) (dentry->d_op->d_revalidate)(dentry, nd); - mutex_lock(&dir->i_mutex); - } + mutex_lock(&dir->i_mutex); } /* _ Patches currently in -mm which might be from raven@xxxxxxxxxx are autofs4-cleanup-expire-code-duplication.patch autofs4-fix-lookup-deadlock.patch autofs4-fix-kernel-includes.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html