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author | tegge <tegge@FreeBSD.org> | 2004-08-12 20:14:49 +0000 |
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committer | tegge <tegge@FreeBSD.org> | 2004-08-12 20:14:49 +0000 |
commit | c5a462b4d9c262be85ebc8bcaf384b7fedf6635f (patch) | |
tree | cdd456b0a228f822484d6c67d1339fd17b892cfe /sys/vm/vm_fault.c | |
parent | f579b621f44c9fd326dcebc027de9a72f7b9e8f3 (diff) | |
download | FreeBSD-src-c5a462b4d9c262be85ebc8bcaf384b7fedf6635f.zip FreeBSD-src-c5a462b4d9c262be85ebc8bcaf384b7fedf6635f.tar.gz |
The vm map lock is needed in vm_fault() after the page has been found,
to avoid later changes before pmap_enter() and vm_fault_prefault()
has completed.
Simplify deadlock avoidance by not blocking on vm map relookup.
In collaboration with: alc
Diffstat (limited to 'sys/vm/vm_fault.c')
-rw-r--r-- | sys/vm/vm_fault.c | 88 |
1 files changed, 37 insertions, 51 deletions
diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c index 4e33b34..8246caa 100644 --- a/sys/vm/vm_fault.c +++ b/sys/vm/vm_fault.c @@ -760,69 +760,55 @@ readrest: * We must verify that the maps have not changed since our last * lookup. */ - if (!fs.lookup_still_valid && - (fs.map->timestamp != map_generation)) { + if (!fs.lookup_still_valid) { vm_object_t retry_object; vm_pindex_t retry_pindex; vm_prot_t retry_prot; - /* - * Unlock vnode before the lookup to avoid deadlock. E.G. - * avoid a deadlock between the inode and exec_map that can - * occur due to locks being obtained in different orders. - */ - if (fs.vp != NULL) { - vput(fs.vp); - fs.vp = NULL; - } - - if (fs.map->infork) { + if (!vm_map_trylock_read(fs.map)) { release_page(&fs); unlock_and_deallocate(&fs); goto RetryFault; } - VM_OBJECT_UNLOCK(fs.object); + fs.lookup_still_valid = TRUE; + if (fs.map->timestamp != map_generation) { + result = vm_map_lookup_locked(&fs.map, vaddr, fault_type, + &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired); - /* - * To avoid trying to write_lock the map while another process - * has it read_locked (in vm_map_wire), we do not try for - * write permission. If the page is still writable, we will - * get write permission. If it is not, or has been marked - * needs_copy, we enter the mapping without write permission, - * and will merely take another fault. - */ - result = vm_map_lookup(&fs.map, vaddr, fault_type & ~VM_PROT_WRITE, - &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired); - map_generation = fs.map->timestamp; + /* + * If we don't need the page any longer, put it on the active + * list (the easiest thing to do here). If no one needs it, + * pageout will grab it eventually. + */ + if (result != KERN_SUCCESS) { + release_page(&fs); + unlock_and_deallocate(&fs); - VM_OBJECT_LOCK(fs.object); - /* - * If we don't need the page any longer, put it on the active - * list (the easiest thing to do here). If no one needs it, - * pageout will grab it eventually. - */ - if (result != KERN_SUCCESS) { - release_page(&fs); - unlock_and_deallocate(&fs); - return (result); - } - fs.lookup_still_valid = TRUE; + /* + * If retry of map lookup would have blocked then + * retry fault from start. + */ + if (result == KERN_FAILURE) + goto RetryFault; + return (result); + } + if ((retry_object != fs.first_object) || + (retry_pindex != fs.first_pindex)) { + release_page(&fs); + unlock_and_deallocate(&fs); + goto RetryFault; + } - if ((retry_object != fs.first_object) || - (retry_pindex != fs.first_pindex)) { - release_page(&fs); - unlock_and_deallocate(&fs); - goto RetryFault; + /* + * Check whether the protection has changed or the object has + * been copied while we left the map unlocked. Changing from + * read to write permission is OK - we leave the page + * write-protected, and catch the write fault. Changing from + * write to read permission means that we can't mark the page + * write-enabled after all. + */ + prot &= retry_prot; } - /* - * Check whether the protection has changed or the object has - * been copied while we left the map unlocked. Changing from - * read to write permission is OK - we leave the page - * write-protected, and catch the write fault. Changing from - * write to read permission means that we can't mark the page - * write-enabled after all. - */ - prot &= retry_prot; } if (prot & VM_PROT_WRITE) { vm_page_lock_queues(); |