Subject: + ipc-share-ids-rwsem-when-possible-in-ipcget_public.patch added to -mm tree
To: davidlohr@xxxxxx,aswin@xxxxxx,manfred@xxxxxxxxxxxxxxxx,riel@xxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Fri, 10 Jan 2014 15:19:35 -0800
The patch titled
Subject: ipc: share ids rwsem when possible in ipcget_public
has been added to the -mm tree. Its filename is
ipc-share-ids-rwsem-when-possible-in-ipcget_public.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ipc-share-ids-rwsem-when-possible-in-ipcget_public.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ipc-share-ids-rwsem-when-possible-in-ipcget_public.patch
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------------------------------------------------------
From: Davidlohr Bueso <davidlohr@xxxxxx>
Subject: ipc: share ids rwsem when possible in ipcget_public
... and rewrite the function. For scenarios where the key is found and
we end up just doing different routinary checks, we can downgrade the
ids->rwsem and share it among concurrent readers. These checks include
the following, which are all safe to share the lock:
ops->more_checks() >> sem_more_checks(), shm_more_checks()
ipc_check_perms() >> ipcperms(),ops->associate() >> [lsm]_[ipctype]_associate()
Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx>
Cc: Aswin Chandramouleeswaran <aswin@xxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/util.c | 58 ++++++++++++++++++++++++++++-----------------------
1 file changed, 32 insertions(+), 26 deletions(-)
diff -puN ipc/util.c~ipc-share-ids-rwsem-when-possible-in-ipcget_public ipc/util.c
--- a/ipc/util.c~ipc-share-ids-rwsem-when-possible-in-ipcget_public
+++ a/ipc/util.c
@@ -183,7 +183,7 @@ void __init ipc_init_proc_interface(cons
* ipc_findkey - find a key in an ipc identifier set
* @ids: ipc identifier set
* @key: key to find
- *
+ *
* Returns the locked pointer to the ipc structure if found or NULL
* otherwise. If key is found ipc points to the owning ipc structure
*
@@ -375,48 +375,54 @@ static int ipc_check_perms(struct ipc_na
* On success, the ipc id is returned.
*/
static int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids,
- struct ipc_ops *ops, struct ipc_params *params)
+ struct ipc_ops *ops, struct ipc_params *params)
{
struct kern_ipc_perm *ipcp;
int flg = params->flg;
- int err;
+ int err = 0;
- /*
- * Take the lock as a writer since we are potentially going to add
- * a new entry + read locks are not "upgradable"
- */
down_write(&ids->rwsem);
ipcp = ipc_findkey(ids, params->key);
- if (ipcp == NULL) {
+
+ if (!ipcp) {
/* key not used */
if (!(flg & IPC_CREAT))
err = -ENOENT;
- else
+ else /* create new ipc object */
err = ops->getnew(ns, params);
- } else {
- /* ipc object has been locked by ipc_findkey() */
- if (flg & IPC_CREAT && flg & IPC_EXCL)
- err = -EEXIST;
- else {
- err = 0;
- if (ops->more_checks)
- err = ops->more_checks(ipcp, params);
- if (!err)
- /*
- * ipc_check_perms returns the IPC id on
- * success
- */
- err = ipc_check_perms(ns, ipcp, ops, params);
- }
+ goto done_write;
+ }
+
+ if ((flg & IPC_CREAT) && (flg & IPC_EXCL)) {
+ /* ipc object was locked by successful ipc_findkey() lookup */
ipc_unlock(ipcp);
+ err = -ENOENT;
+
+ goto done_write;
}
- up_write(&ids->rwsem);
+ /*
+ * The key was found, so we will just perform routinary checks on
+ * ipc the object. Share the lock among other readers.
+ */
+ downgrade_write(&ids->rwsem);
+
+ if (ops->more_checks)
+ err = ops->more_checks(ipcp, params);
+ if (!err)
+ /* returns the IPC id on success */
+ err = ipc_check_perms(ns, ipcp, ops, params);
+
+ ipc_unlock(ipcp);
+
+ up_read(&ids->rwsem);
+ return err;
+done_write:
+ up_write(&ids->rwsem);
return err;
}
-
/**
* ipc_rmid - remove an ipc identifier
* @ids: ipc identifier set
_
Patches currently in -mm which might be from davidlohr@xxxxxx are
x86-mm-account-for-tlb-flushes-only-when-debugging.patch
x86-mm-clean-up-inconsistencies-when-flushing-tlb-ranges.patch
x86-mm-eliminate-redundant-page-table-walk-during-tlb-range-flushing.patch
x86-mm-change-tlb_flushall_shift-for-ivybridge.patch
mm-x86-revisit-tlb_flushall_shift-tuning-for-page-flushes-except-on-ivybridge.patch
mm-mmapc-add-mlock_future_check-helper.patch
mm-mlock-prepare-params-outside-critical-region.patch
partitions-efi-complete-documentation-of-gpt-kernel-param-purpose.patch
ipc-semc-avoid-overflow-of-semop-undo-semadj-value.patch
ipc-semc-avoid-overflow-of-semop-undo-semadj-value-fix.patch
ipc-semc-avoid-overflow-of-semop-undo-semadj-value-fix-2.patch
ipc-introduce-ipc_valid_object-helper-to-sort-out-ipc_rmid-races.patch
ipc-change-kern_ipc_permdeleted-type-to-bool.patch
ipc-whitespace-cleanup.patch
ipc-standardize-code-comments.patch
ipc-remove-braces-for-single-statements.patch
ipc-remove-useless-return-statement.patch
ipc-simplify-sysvipc_proc_open-return.patch
ipc-delete-seq_max-field-in-struct-ipc_ids.patch
ipc-share-ids-rwsem-when-possible-in-ipcget_public.patch
ipcmsg-document-barriers.patch
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