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futex: Fix inode life-time issue

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As reported by Jann, ihold() does not in fact guarantee inode
persistence. And instead of making it so, replace the usage of inode
pointers with a per boot, machine wide, unique inode identifier.

This sequence number is global, but shared (file backed) futexes are
rare enough that this should not become a performance issue.

Reported-by: Jann Horn <jannh@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
This commit is contained in:
Peter Zijlstra 2020-03-04 11:28:31 +01:00
parent 98d54f81e3
commit 8019ad13ef
4 changed files with 65 additions and 43 deletions
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17
include/linux/futex.h
View file

@ -31,23 +31,26 @@ struct task_struct;
union futex_key {
struct {
u64 i_seq;
unsigned long pgoff;
struct inode *inode;
int offset;
unsigned int offset;
} shared;
struct {
union {
struct mm_struct *mm;
u64 __tmp;
};
unsigned long address;
struct mm_struct *mm;
int offset;
unsigned int offset;
} private;
struct {
u64 ptr;
unsigned long word;
void *ptr;
int offset;
unsigned int offset;
} both;
};
#define FUTEX_KEY_INIT (union futex_key) { .both = { .ptr = NULL } }
#define FUTEX_KEY_INIT (union futex_key) { .both = { .ptr = 0ULL } }
#ifdef CONFIG_FUTEX
enum {