.

wcfs/client/wcfs.cpp

@@ -1055,6 +1055,7 @@ pair<Mapping, error> _FileH::mmap(int64_t blk_start, int64_t blk_len, VMA *vma)
     mmap->mem_start = mem_start;
     mmap->mem_stop  = mem_stop;
     mmap->vma       = vma;
+    mmap->efaulted  = false;
 
     for (auto _ : f._pinned) {  // TODO keep f._pinned ↑blk and use binary search
         int64_t    blk = _.first;
@@ -1103,6 +1104,22 @@ error _Mapping::__remmapAsEfault() {
     etrace("");
 
     error err = mmap_efault_into(mmap.mem_start, mmap.mem_stop - mmap.mem_start);
+    mmap.efaulted = true;
+    return E(err);
+}
+
+// __remmapBlkAsEfault is similar to __remmapAsEfault, but remmaps memory of only 1 block.
+// blk must be in mapped range.
+error _Mapping::__remmapBlkAsEfault(int64_t blk) {
+    _Mapping& mmap = *this;
+    FileH f = mmap.fileh;
+
+    xerr::Contextf E("%s: remmapblk #%ld as efault", v(mmap), blk);
+    etrace("");
+
+    ASSERT(mmap.blk_start <= blk && blk < mmap.blk_stop());
+    uint8_t *blkmem = mmap.mem_start + (blk - mmap.blk_start)*f->blksize;
+    error err = mmap_efault_into(blkmem, 1*f->blksize);
     return E(err);
 }
 
@@ -1158,11 +1175,12 @@ error _Mapping::unmap() {
 // at=TidHead means unpin to head/ .
 // NOTE this does not check whether virtmem already mapped blk as RW.
 //
+// _remmapblk must not be called after Mapping is switched to efault.
+//
 // The following locks must be held by caller:
 // - f.wconn.atMu
 // - f._mmapMu
 error _Mapping::_remmapblk(int64_t blk, zodb::Tid at) {
-    // XXX must not be called after Mapping is switched to efault?
 
     _Mapping *mmap = this;
     FileH f = mmap->fileh;
@@ -1170,9 +1188,12 @@ error _Mapping::_remmapblk(int64_t blk, zodb::Tid at) {
     etrace("");
 
     ASSERT(mmap->blk_start <= blk && blk < mmap->blk_stop());
-    error err;
+    // a mmapping is efaulted only for closed files, i.e. fileh is removed from wconn._filehTab
+    // -> pinner should not see the fileh and so shuold not see this mapping.
+    ASSERT(!mmap->efaulted);
 
     uint8_t *blkmem = mmap->mem_start + (blk - mmap->blk_start)*f->blksize;
+    error err;
     os::File fsfile;
     bool fclose = false;
     if (at == TidHead) {
@@ -1218,11 +1239,13 @@ error _Mapping::_remmapblk(int64_t blk, zodb::Tid at) {
 // remmap_blk remmaps file[blk] in its place again.
 //
 // Virtmem calls Mapping.remmap_blk under virtmem lock to remmap a block after
-// RW dirty page was e.g. discarded.
+// RW dirty page was e.g. discarded or committed.
 error _Mapping::remmap_blk(int64_t blk) {
     _Mapping& mmap = *this;
     FileH f = mmap.fileh;
 
+    error err;
+
     // NOTE virtmem lock is held by virtmem caller
     f->wconn->_atMu.RLock();
     f->_mmapMu.lock();
@@ -1234,7 +1257,12 @@ error _Mapping::remmap_blk(int64_t blk) {
     if (!(mmap.blk_start <= blk && blk < mmap.blk_stop()))
         panic("remmap_blk: blk out of Mapping range");
 
-    // XXX do nothing after mapping is switched to efault? (i.e. f is closed/down)
+    // it should not happen, but if, for a efaulted mapping, virtmem asks us to
+    // remmap base-layer blk memory in its place again, we reinject efault into it.
+    if (mmap.efaulted) {
+        log::Warnf("%s: remmapblk called for already-efaulted mapping", v(mmap));
+        return mmap.__remmapBlkAsEfault(blk); // TODO recheck errctx
+    }
 
     // blkrev = rev | @head
     zodb::Tid blkrev; bool ok;
@@ -1242,7 +1270,7 @@ error _Mapping::remmap_blk(int64_t blk) {
     if (!ok)
         blkrev = TidHead;
 
-    error err = mmap._remmapblk(blk, blkrev);
+    err = mmap._remmapblk(blk, blkrev);
     if (err != nil)
         return err; // errctx is good in _remmapblk
 

wcfs/client/wcfs.h

@@ -282,6 +282,7 @@ struct _Mapping : object {
     uint8_t  *mem_start;    // mmapped memory [mem_start, mem_stop)
     uint8_t  *mem_stop;
     VMA      *vma;          // mmapped under this virtmem VMA | nil if created standalone from virtmem
+    bool     efaulted;      // y after mapping was switched to be invalid (gives SIGSEGV on access)
 
     int64_t blk_stop() const {
         ASSERT((mem_stop - mem_start) % fileh->blksize == 0);
@@ -294,6 +295,7 @@ struct _Mapping : object {
     void  _assertVMAOk();
     error _remmapblk(int64_t blk, zodb::Tid at);
     error __remmapAsEfault();
+    error __remmapBlkAsEfault(int64_t blk);
 
     // don't new - create via FileH.mmap
 private: