From: Al Viro <viro@zeniv.linux.org.uk>
To: David Howells <dhowells@redhat.com>
Cc: torvalds@linux-foundation.org, Ted Ts'o <tytso@mit.edu>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
willy@infradead.org, linux-mm@kvack.org,
linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"?
Date: Tue, 22 Jun 2021 15:27:43 +0000 [thread overview]
Message-ID: <YNIBb5WPrk8nnKKn@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <3221175.1624375240@warthog.procyon.org.uk>
On Tue, Jun 22, 2021 at 04:20:40PM +0100, David Howells wrote:
> and wondering if the iov_iter_fault_in_readable() is actually effective. Yes,
> it can make sure that the page we're intending to modify is dragged into the
> pagecache and marked uptodate so that it can be read from, but is it possible
> for the page to then get reclaimed before we get to
> iov_iter_copy_from_user_atomic()? a_ops->write_begin() could potentially take
> a long time, say if it has to go and get a lock/lease from a server.
Yes, it is. So what? We'll just retry. You *can't* take faults while holding
some pages locked; not without shitloads of deadlocks.
next prev parent reply other threads:[~2021-06-22 15:28 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-22 15:20 Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"? David Howells
2021-06-22 15:27 ` Al Viro [this message]
2021-06-22 15:36 ` Al Viro
2021-06-22 17:25 ` Matthew Wilcox
2021-06-22 17:39 ` Linus Torvalds
2021-06-22 17:55 ` David Howells
2021-06-22 18:04 ` Matthew Wilcox
2021-06-22 18:07 ` Linus Torvalds
2021-06-22 18:16 ` Nadav Amit
2021-06-22 18:23 ` Matthew Wilcox
2021-06-22 18:28 ` Linus Torvalds
2021-06-22 18:36 ` Matthew Wilcox
2021-06-22 18:51 ` Nadav Amit
2021-06-22 18:57 ` Linus Torvalds
2021-06-22 18:23 ` David Howells
2021-06-22 18:32 ` Linus Torvalds
2021-06-22 18:13 ` David Howells
2021-06-22 15:32 ` Linus Torvalds
2021-06-22 15:53 ` Linus Torvalds
2021-06-22 15:32 ` Matthew Wilcox
2021-06-22 16:27 ` David Howells
2021-06-22 21:55 ` David Laight
2021-06-22 22:04 ` Matthew Wilcox
2021-06-22 22:31 ` David Laight
2021-06-22 22:20 ` Dave Chinner
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