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| author | Alexey Dobriyan <adobriyan@gmail.com> | 2016-12-12 16:45:22 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-12-12 18:55:09 -0800 |
| commit | 492b2da6056e7051917516368e75e062422c3557 (patch) | |
| tree | 808bc51279edffc50b3513a215771668919770d1 | |
| parent | 39a10ac23cfdb6469550e1641a2bc2ed80663ceb (diff) | |
| download | linux-492b2da6056e7051917516368e75e062422c3557.tar.bz2 | |
proc: tweak comments about 2 stage open and everything
Some comments were obsoleted since commit 05c0ae21c034 ("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: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | fs/proc/inode.c | 29 |
1 files changed, 21 insertions, 8 deletions
diff --git a/fs/proc/inode.c b/fs/proc/inode.c index 57f548e2eb59..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); @@ -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); |