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-rw-r--r--fs/proc/inode.c37
1 files changed, 26 insertions, 11 deletions
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index e69ebe648a34..783bc19644d1 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -138,6 +138,16 @@ static void unuse_pde(struct proc_dir_entry *pde)
/* pde is locked */
static void close_pdeo(struct proc_dir_entry *pde, struct pde_opener *pdeo)
{
+ /*
+ * close() (proc_reg_release()) can't delete an entry and proceed:
+ * ->release hook needs to be available at the right moment.
+ *
+ * rmmod (remove_proc_entry() et al) can't delete an entry and proceed:
+ * "struct file" needs to be available at the right moment.
+ *
+ * Therefore, first process to enter this function does ->release() and
+ * signals its completion to the other process which does nothing.
+ */
if (pdeo->closing) {
/* somebody else is doing that, just wait */
DECLARE_COMPLETION_ONSTACK(c);
@@ -147,12 +157,13 @@ static void close_pdeo(struct proc_dir_entry *pde, struct pde_opener *pdeo)
spin_lock(&pde->pde_unload_lock);
} else {
struct file *file;
- pdeo->closing = 1;
+ pdeo->closing = true;
spin_unlock(&pde->pde_unload_lock);
file = pdeo->file;
pde->proc_fops->release(file_inode(file), file);
spin_lock(&pde->pde_unload_lock);
- list_del_init(&pdeo->lh);
+ /* After ->release. */
+ list_del(&pdeo->lh);
if (pdeo->c)
complete(pdeo->c);
kfree(pdeo);
@@ -167,6 +178,8 @@ void proc_entry_rundown(struct proc_dir_entry *de)
if (atomic_add_return(BIAS, &de->in_use) != BIAS)
wait_for_completion(&c);
+ /* ->pde_openers list can't grow from now on. */
+
spin_lock(&de->pde_unload_lock);
while (!list_empty(&de->pde_openers)) {
struct pde_opener *pdeo;
@@ -312,16 +325,17 @@ static int proc_reg_open(struct inode *inode, struct file *file)
struct pde_opener *pdeo;
/*
- * What for, you ask? Well, we can have open, rmmod, remove_proc_entry
- * sequence. ->release won't be called because ->proc_fops will be
- * cleared. Depending on complexity of ->release, consequences vary.
+ * Ensure that
+ * 1) PDE's ->release hook will be called no matter what
+ * either normally by close()/->release, or forcefully by
+ * rmmod/remove_proc_entry.
+ *
+ * 2) rmmod isn't blocked by opening file in /proc and sitting on
+ * the descriptor (including "rmmod foo </proc/foo" scenario).
*
- * We can't wait for mercy when close will be done for real, it's
- * deadlockable: rmmod foo </proc/foo . So, we're going to do ->release
- * by hand in remove_proc_entry(). For this, save opener's credentials
- * for later.
+ * Save every "struct file" with custom ->release hook.
*/
- pdeo = kzalloc(sizeof(struct pde_opener), GFP_KERNEL);
+ pdeo = kmalloc(sizeof(struct pde_opener), GFP_KERNEL);
if (!pdeo)
return -ENOMEM;
@@ -338,7 +352,8 @@ static int proc_reg_open(struct inode *inode, struct file *file)
if (rv == 0 && release) {
/* To know what to release. */
pdeo->file = file;
- /* Strictly for "too late" ->release in proc_reg_release(). */
+ pdeo->closing = false;
+ pdeo->c = NULL;
spin_lock(&pde->pde_unload_lock);
list_add(&pdeo->lh, &pde->pde_openers);
spin_unlock(&pde->pde_unload_lock);