Author: markj Date: Mon Feb 17 15:10:41 2020 New Revision: 358025 URL: https://svnweb.freebsd.org/changeset/base/358025
Log: Fix a swap block allocation race. putpages' allocation of swap blocks is done under the global sw_dev lock. Previously it would drop that lock before inserting the allocated blocks into the object's trie, creating a window in which swap blocks are allocated but are not visible to swapoff. This can cause swp_pager_strategy() to fail and panic the system. Fix the problem bluntly, by allocating swap blocks under the object lock. Reviewed by: jeff, kib Tested by: pho MFC after: 2 weeks Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D23665 Modified: head/sys/vm/swap_pager.c Modified: head/sys/vm/swap_pager.c ============================================================================== --- head/sys/vm/swap_pager.c Mon Feb 17 15:09:40 2020 (r358024) +++ head/sys/vm/swap_pager.c Mon Feb 17 15:10:41 2020 (r358025) @@ -1453,18 +1453,6 @@ swap_pager_putpages(vm_object_t object, vm_page_t *ma, /* Maximum I/O size is limited by maximum swap block size. */ n = min(count - i, nsw_cluster_max); - /* Get a block of swap of size up to size n. */ - blk = swp_pager_getswapspace(&n, 4); - if (blk == SWAPBLK_NONE) { - for (j = 0; j < n; ++j) - rtvals[i + j] = VM_PAGER_FAIL; - continue; - } - - /* - * All I/O parameters have been satisfied. Build the I/O - * request and assign the swap space. - */ if (async) { mtx_lock(&swbuf_mtx); while (nsw_wcount_async == 0) @@ -1473,19 +1461,20 @@ swap_pager_putpages(vm_object_t object, vm_page_t *ma, nsw_wcount_async--; mtx_unlock(&swbuf_mtx); } - bp = uma_zalloc(swwbuf_zone, M_WAITOK); - if (async) - bp->b_flags = B_ASYNC; - bp->b_flags |= B_PAGING; - bp->b_iocmd = BIO_WRITE; - bp->b_rcred = crhold(thread0.td_ucred); - bp->b_wcred = crhold(thread0.td_ucred); - bp->b_bcount = PAGE_SIZE * n; - bp->b_bufsize = PAGE_SIZE * n; - bp->b_blkno = blk; - + /* Get a block of swap of size up to size n. */ VM_OBJECT_WLOCK(object); + blk = swp_pager_getswapspace(&n, 4); + if (blk == SWAPBLK_NONE) { + VM_OBJECT_WUNLOCK(object); + mtx_lock(&swbuf_mtx); + if (++nsw_wcount_async == 1) + wakeup(&nsw_wcount_async); + mtx_unlock(&swbuf_mtx); + for (j = 0; j < n; ++j) + rtvals[i + j] = VM_PAGER_FAIL; + continue; + } for (j = 0; j < n; ++j) { mreq = ma[i + j]; vm_page_aflag_clear(mreq, PGA_SWAP_FREE); @@ -1496,10 +1485,24 @@ swap_pager_putpages(vm_object_t object, vm_page_t *ma, addr); MPASS(mreq->dirty == VM_PAGE_BITS_ALL); mreq->oflags |= VPO_SWAPINPROG; - bp->b_pages[j] = mreq; } VM_OBJECT_WUNLOCK(object); + + bp = uma_zalloc(swwbuf_zone, M_WAITOK); + if (async) + bp->b_flags = B_ASYNC; + bp->b_flags |= B_PAGING; + bp->b_iocmd = BIO_WRITE; + + bp->b_rcred = crhold(thread0.td_ucred); + bp->b_wcred = crhold(thread0.td_ucred); + bp->b_bcount = PAGE_SIZE * n; + bp->b_bufsize = PAGE_SIZE * n; + bp->b_blkno = blk; + for (j = 0; j < n; j++) + bp->b_pages[j] = ma[i + j]; bp->b_npages = n; + /* * Must set dirty range for NFS to work. */ @@ -2059,7 +2062,7 @@ allocated: * Free the swblk if we end up with the empty page run. */ if (swapblk == SWAPBLK_NONE) - swp_pager_free_empty_swblk(object, sb); + swp_pager_free_empty_swblk(object, sb); return (prev_swapblk); } _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
