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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH v2 1/3] afs: Handle len being extending over page end in write_begin/write_end From: David Howells To: linux-cachefs@redhat.com, linux-afs@lists.infradead.org Cc: "Matthew Wilcox (Oracle)" , Jeff Layton , dhowells@redhat.com, Jeff Layton , "Matthew Wilcox (Oracle)" , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 17 Jun 2021 09:24:02 +0100 Message-ID: <162391824293.1173366.15452474691364794223.stgit@warthog.procyon.org.uk> In-Reply-To: <162391823192.1173366.9740514875196345746.stgit@warthog.procyon.org.uk> References: <162391823192.1173366.9740514875196345746.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.23 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org With transparent huge pages, in the future, write_begin() and write_end() may be passed a length parameter that, in combination with the offset into the page, exceeds the length of that page. This allows grab_cache_page_write_begin() to better choose the size of THP to allocate. Fix afs's functions to handle this by trimming the length as needed after the page has been allocated. [Removed the now-unnecessary index var; spotted by kernel test robot] Fixes: e1b1240c1ff5 ("netfs: Add write_begin helper") Reported-by: Matthew Wilcox (Oracle) Signed-off-by: David Howells Acked-by: Jeff Layton cc: linux-afs@lists.infradead.org Link: https://lore.kernel.org/r/162367681795.460125.11729955608839747375.stgit@warthog.procyon.org.uk/ # v1 --- fs/afs/write.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/fs/afs/write.c b/fs/afs/write.c index a523bb86915d..56e2cff2cb87 100644 --- a/fs/afs/write.c +++ b/fs/afs/write.c @@ -25,7 +25,8 @@ int afs_set_page_dirty(struct page *page) } /* - * prepare to perform part of a write to a page + * Prepare to perform part of a write to a page. Note that len may extend + * beyond the end of the page. */ int afs_write_begin(struct file *file, struct address_space *mapping, loff_t pos, unsigned len, unsigned flags, @@ -36,7 +37,6 @@ int afs_write_begin(struct file *file, struct address_space *mapping, unsigned long priv; unsigned f, from; unsigned t, to; - pgoff_t index; int ret; _enter("{%llx:%llu},%llx,%x", @@ -51,8 +51,8 @@ int afs_write_begin(struct file *file, struct address_space *mapping, if (ret < 0) return ret; - index = page->index; - from = pos - index * PAGE_SIZE; + from = offset_in_thp(page, pos); + len = min_t(size_t, len, thp_size(page) - from); to = from + len; try_again: @@ -103,7 +103,8 @@ int afs_write_begin(struct file *file, struct address_space *mapping, } /* - * finalise part of a write to a page + * Finalise part of a write to a page. Note that len may extend beyond the end + * of the page. */ int afs_write_end(struct file *file, struct address_space *mapping, loff_t pos, unsigned len, unsigned copied, @@ -111,7 +112,7 @@ int afs_write_end(struct file *file, struct address_space *mapping, { struct afs_vnode *vnode = AFS_FS_I(file_inode(file)); unsigned long priv; - unsigned int f, from = pos & (thp_size(page) - 1); + unsigned int f, from = offset_in_thp(page, pos); unsigned int t, to = from + copied; loff_t i_size, maybe_i_size;