From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 029/155] mm/filemap.c: don't bother dropping mmap_sem for zero size readahead Date: Wed, 01 Apr 2020 21:04:40 -0700 Message-ID: <20200402040440.RCDEWJbKc%akpm@linux-foundation.org> References: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:50574 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726136AbgDBEEl (ORCPT ); Thu, 2 Apr 2020 00:04:41 -0400 In-Reply-To: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, jack@suse.cz, josef@toxicpanda.com, linux-mm@kvack.org, minchan@kernel.org, mm-commits@vger.kernel.org, snazy@gmx.de, torvalds@linux-foundation.org From: Jan Kara Subject: mm/filemap.c: don't bother dropping mmap_sem for zero size readahead When handling a page fault, we drop mmap_sem to start async readahead so that we don't block on IO submission with mmap_sem held. However there's no point to drop mmap_sem in case readahead is disabled. Handle that case to avoid pointless dropping of mmap_sem and retrying the fault. This was actually reported to block mlockall(MCL_CURRENT) indefinitely. Link: http://lkml.kernel.org/r/20200212101356.30759-1-jack@suse.cz Fixes: 6b4c9f446981 ("filemap: drop the mmap_sem for all blocking operations") Signed-off-by: Jan Kara Reported-by: Minchan Kim Reported-by: Robert Stupp Reviewed-by: Josef Bacik Reviewed-by: Minchan Kim Signed-off-by: Andrew Morton --- mm/filemap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/filemap.c~mm-dont-bother-dropping-mmap_sem-for-zero-size-readahead +++ a/mm/filemap.c @@ -2416,7 +2416,7 @@ static struct file *do_async_mmap_readah pgoff_t offset = vmf->pgoff; /* If we don't want any read-ahead, don't bother */ - if (vmf->vma->vm_flags & VM_RAND_READ) + if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages) return fpin; if (ra->mmap_miss > 0) ra->mmap_miss--; _