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Diffstat (limited to 'doc/SMPNOTES')
| -rw-r--r-- | doc/SMPNOTES | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/doc/SMPNOTES b/doc/SMPNOTES new file mode 100644 index 0000000..ba54836 --- /dev/null +++ b/doc/SMPNOTES @@ -0,0 +1,21 @@ +Notes on the (20000210) SMP-ization of the bridging code: + +Each bridge has a hash table of MAC addresses. This table is protected +by a rwlock hash_lock. The entries are refcounted; 'getting' an entry +is done in the usual way: read_lock the table, find the entry, +increment it's refcount and unlock the table. Bottom half context +acquires this lock in read as well as write mode, therefore we always +need to locally disable BHs when acquiring this lock. + +Each bridge also has an rwlock called lock. This slightly misnamed +lock protects the bridge's port_list. All stp code acquires this lock +in read mode, the only piece of code that acquires this lock in write +mode is the ioctl code (br_ioctl.c). Bottom halves never acquire this +lock in write mode, therefore we can use read_lock instead of +read_lock_bh in all cases. + +All ioctls are globally serialized by the semaphore ioctl_mutex. All +code which acquires the bridge lock in write mode also acquires +ioctl_mutex. Therefore, if we have already grabbed ioctl_mutex we +don't need to read_lock the bridge lock anymore; the ioctl_mutex will +protect against concurrent writers. |