cifs: on CONFIG_HIGHMEM machines, limit the rsize/wsize to the kmap space (3ae629d9) · Commits · 戴 / test

We currently rely on being able to kmap all of the pages in an async read or write request. If you're on a machine that has CONFIG_HIGHMEM set then that kmap space is limited, sometimes to as low as 512 slots. With 512 slots, we can only support up to a 2M r/wsize, and that's assuming that we can get our greedy little hands on all of them. There are other users however, so it's possible we'll end up stuck with a size that large. Since we can't handle a rsize or wsize larger than that currently, cap those options at the number of kmap slots we have. We could consider capping it even lower, but we currently default to a max of 1M. Might as well allow those luddites on 32 bit arches enough rope to hang themselves. A more robust fix would be to teach the send and receive routines how to contend with an array of pages so we don't need to marshal up a kvec array at all. That's a fairly significant overhaul though, so we'll need this limit in place until that's ready. Cc: <stable@vger.kernel.org> Reported-by:

Jian Li <jiali@redhat.com> Signed-off-by:

Jeff Layton <jlayton@redhat.com> Signed-off-by:

Steve French <smfrench@gmail.com>

fs/cifs/connect.c

+18 −0

Original line number	Diff line number	Diff line
		@@ -3445,6 +3445,18 @@ void cifs_setup_cifs_sb(struct smb_vol *pvolume_info,
		#define CIFS_DEFAULT_NON_POSIX_RSIZE (60 * 1024)
		#define CIFS_DEFAULT_NON_POSIX_WSIZE (65536)

		/*
		* On hosts with high memory, we can't currently support wsize/rsize that are
		* larger than we can kmap at once. Cap the rsize/wsize at
		* LAST_PKMAP * PAGE_SIZE. We'll never be able to fill a read or write request
		* larger than that anyway.
		*/
		#ifdef CONFIG_HIGHMEM
		#define CIFS_KMAP_SIZE_LIMIT (LAST_PKMAP * PAGE_CACHE_SIZE)
		#else /* CONFIG_HIGHMEM */
		#define CIFS_KMAP_SIZE_LIMIT (1<<24)
		#endif /* CONFIG_HIGHMEM */

		static unsigned int
		cifs_negotiate_wsize(struct cifs_tcon tcon, struct smb_vol pvolume_info)
		{
		@@ -3475,6 +3487,9 @@ cifs_negotiate_wsize(struct cifs_tcon tcon, struct smb_vol pvolume_info)
		wsize = min_t(unsigned int, wsize,
		server->maxBuf - sizeof(WRITE_REQ) + 4);

		/* limit to the amount that we can kmap at once */
		wsize = min_t(unsigned int, wsize, CIFS_KMAP_SIZE_LIMIT);

		/* hard limit of CIFS_MAX_WSIZE */
		wsize = min_t(unsigned int, wsize, CIFS_MAX_WSIZE);

		@@ -3516,6 +3531,9 @@ cifs_negotiate_rsize(struct cifs_tcon tcon, struct smb_vol pvolume_info)
		if (!(server->capabilities & CAP_LARGE_READ_X))
		rsize = min_t(unsigned int, CIFSMaxBufSize, rsize);

		/* limit to the amount that we can kmap at once */
		rsize = min_t(unsigned int, rsize, CIFS_KMAP_SIZE_LIMIT);

		/* hard limit of CIFS_MAX_RSIZE */
		rsize = min_t(unsigned int, rsize, CIFS_MAX_RSIZE);

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