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authorWaiman Long <longman@redhat.com>2019-05-15 01:46:29 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2019-05-15 05:52:52 +0300
commit5ac893b8cb10fe2a47a77780d37f9bf5b142854b (patch)
tree9d6dcab9f8540b997090f6870a0470cf6bfd06cc /ipc/util.h
parenta5091fda4e3c202aeb1728a86d0fcd20fd0f4f5e (diff)
downloadlinux-5ac893b8cb10fe2a47a77780d37f9bf5b142854b.tar.xz
ipc: allow boot time extension of IPCMNI from 32k to 16M
The maximum number of unique System V IPC identifiers was limited to 32k. That limit should be big enough for most use cases. However, there are some users out there requesting for more, especially those that are migrating from Solaris which uses 24 bits for unique identifiers. To satisfy the need of those users, a new boot time kernel option "ipcmni_extend" is added to extend the IPCMNI value to 16M. This is a 512X increase which should be big enough for users out there that need a large number of unique IPC identifier. The use of this new option will change the pattern of the IPC identifiers returned by functions like shmget(2). An application that depends on such pattern may not work properly. So it should only be used if the users really need more than 32k of unique IPC numbers. This new option does have the side effect of reducing the maximum number of unique sequence numbers from 64k down to 128. So it is a trade-off. The computation of a new IPC id is not done in the performance critical path. So a little bit of additional overhead shouldn't have any real performance impact. Link: http://lkml.kernel.org/r/20190329204930.21620-1-longman@redhat.com Signed-off-by: Waiman Long <longman@redhat.com> Acked-by: Manfred Spraul <manfred@colorfullife.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: "Eric W . Biederman" <ebiederm@xmission.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Kees Cook <keescook@chromium.org> Cc: "Luis R. Rodriguez" <mcgrof@kernel.org> Cc: Matthew Wilcox <willy@infradead.org> Cc: Takashi Iwai <tiwai@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc/util.h')
-rw-r--r--ipc/util.h44
1 files changed, 35 insertions, 9 deletions
diff --git a/ipc/util.h b/ipc/util.h
index e272be622ae7..9746886757de 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -15,8 +15,34 @@
#include <linux/err.h>
#include <linux/ipc_namespace.h>
-#define IPCMNI 32768 /* <= MAX_INT limit for ipc arrays (including sysctl changes) */
-#define SEQ_MULTIPLIER (IPCMNI)
+/*
+ * The IPC ID contains 2 separate numbers - index and sequence number.
+ * By default,
+ * bits 0-14: index (32k, 15 bits)
+ * bits 15-30: sequence number (64k, 16 bits)
+ *
+ * When IPCMNI extension mode is turned on, the composition changes:
+ * bits 0-23: index (16M, 24 bits)
+ * bits 24-30: sequence number (128, 7 bits)
+ */
+#define IPCMNI_SHIFT 15
+#define IPCMNI_EXTEND_SHIFT 24
+#define IPCMNI (1 << IPCMNI_SHIFT)
+#define IPCMNI_EXTEND (1 << IPCMNI_EXTEND_SHIFT)
+
+#ifdef CONFIG_SYSVIPC_SYSCTL
+extern int ipc_mni;
+extern int ipc_mni_shift;
+
+#define IPCMNI_SEQ_SHIFT ipc_mni_shift
+#define IPCMNI_IDX_MASK ((1 << ipc_mni_shift) - 1)
+
+#else /* CONFIG_SYSVIPC_SYSCTL */
+
+#define ipc_mni IPCMNI
+#define IPCMNI_SEQ_SHIFT IPCMNI_SHIFT
+#define IPCMNI_IDX_MASK ((1 << IPCMNI_SHIFT) - 1)
+#endif /* CONFIG_SYSVIPC_SYSCTL */
void sem_init(void);
void msg_init(void);
@@ -96,9 +122,9 @@ struct pid_namespace *ipc_seq_pid_ns(struct seq_file *);
#define IPC_MSG_IDS 1
#define IPC_SHM_IDS 2
-#define ipcid_to_idx(id) ((id) % SEQ_MULTIPLIER)
-#define ipcid_to_seqx(id) ((id) / SEQ_MULTIPLIER)
-#define IPCID_SEQ_MAX min_t(int, INT_MAX/SEQ_MULTIPLIER, USHRT_MAX)
+#define ipcid_to_idx(id) ((id) & IPCMNI_IDX_MASK)
+#define ipcid_to_seqx(id) ((id) >> IPCMNI_SEQ_SHIFT)
+#define IPCID_SEQ_MAX (INT_MAX >> IPCMNI_SEQ_SHIFT)
/* must be called with ids->rwsem acquired for writing */
int ipc_addid(struct ipc_ids *, struct kern_ipc_perm *, int);
@@ -123,8 +149,8 @@ static inline int ipc_get_maxidx(struct ipc_ids *ids)
if (ids->in_use == 0)
return -1;
- if (ids->in_use == IPCMNI)
- return IPCMNI - 1;
+ if (ids->in_use == ipc_mni)
+ return ipc_mni - 1;
return ids->max_idx;
}
@@ -216,10 +242,10 @@ void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
static inline int sem_check_semmni(struct ipc_namespace *ns) {
/*
- * Check semmni range [0, IPCMNI]
+ * Check semmni range [0, ipc_mni]
* semmni is the last element of sem_ctls[4] array
*/
- return ((ns->sem_ctls[3] < 0) || (ns->sem_ctls[3] > IPCMNI))
+ return ((ns->sem_ctls[3] < 0) || (ns->sem_ctls[3] > ipc_mni))
? -ERANGE : 0;
}