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Commit 492b2da6 authored by Alexey Dobriyan's avatar Alexey Dobriyan Committed by Linus Torvalds
Browse files

proc: tweak comments about 2 stage open and everything 

Some comments were obsoleted since commit 05c0ae21 ("try a saner
locking for pde_opener...").

Some new comments added.

Some confusing comments replaced with equally confusing ones.

Link: http://lkml.kernel.org/r/20161029160231.GD1246@avx2


Signed-off-by: default avatarAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 39a10ac2

fs/proc/inode.c

+21 −8
Original line number Diff line number Diff line
@@ -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);
@@ -152,6 +162,7 @@ static void close_pdeo(struct proc_dir_entry *pde, struct pde_opener *pdeo) 
		file = pdeo->file;

		pde->proc_fops->release(file_inode(file), file);

		spin_lock(&pde->pde_unload_lock);

		/* After ->release. */

		list_del(&pdeo->lh);

		if (pdeo->c)

			complete(pdeo->c);
@@ -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;
@@ -312,14 +325,15 @@ 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 = kmalloc(sizeof(struct pde_opener), GFP_KERNEL);

	if (!pdeo)
@@ -340,7 +354,6 @@ static int proc_reg_open(struct inode *inode, struct file *file) 
		pdeo->file = file;

		pdeo->closing = false;

		pdeo->c = NULL;

		/* Strictly for "too late" ->release in proc_reg_release(). */

		spin_lock(&pde->pde_unload_lock);

		list_add(&pdeo->lh, &pde->pde_openers);

		spin_unlock(&pde->pde_unload_lock);