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Commit 10c12851 authored by Ilya Dryomov's avatar Ilya Dryomov
Browse files

libceph: avoid a __vmalloc() deadlock in ceph_kvmalloc() 



The vmalloc allocator doesn't fully respect the specified gfp mask:
while the actual pages are allocated as requested, the page table pages
are always allocated with GFP_KERNEL.  ceph_kvmalloc() may be called
with GFP_NOFS and GFP_NOIO (for ceph and rbd respectively), so this may
result in a deadlock.

There is no real reason for the current PAGE_ALLOC_COSTLY_ORDER logic,
it's just something that seemed sensible at the time (ceph_kvmalloc()
predates kvmalloc()).  kvmalloc() is smarter: in an attempt to reduce
long term fragmentation, it first tries to kmalloc non-disruptively.

Switch to kvmalloc() and set the respective PF_MEMALLOC_* flag using
the scope API to avoid the deadlock.  Note that kvmalloc() needs to be
passed GFP_KERNEL to enable the fallback.

Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
parent 6fd4e634

net/ceph/ceph_common.c

+23 −6
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ 
#include <linux/nsproxy.h>

#include <linux/parser.h>

#include <linux/sched.h>

#include <linux/sched/mm.h>

#include <linux/seq_file.h>

#include <linux/slab.h>

#include <linux/statfs.h>
@@ -185,18 +186,34 @@ int ceph_compare_options(struct ceph_options *new_opt, 
}

EXPORT_SYMBOL(ceph_compare_options);



/*

 * kvmalloc() doesn't fall back to the vmalloc allocator unless flags are

 * compatible with (a superset of) GFP_KERNEL.  This is because while the

 * actual pages are allocated with the specified flags, the page table pages

 * are always allocated with GFP_KERNEL.  map_vm_area() doesn't even take

 * flags because GFP_KERNEL is hard-coded in {p4d,pud,pmd,pte}_alloc().

 *

 * ceph_kvmalloc() may be called with GFP_KERNEL, GFP_NOFS or GFP_NOIO.

 */

void *ceph_kvmalloc(size_t size, gfp_t flags)

{

	if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {

		void *ptr = kmalloc(size, flags | __GFP_NOWARN);

		if (ptr)

			return ptr;

	void *p;



	if ((flags & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS)) {

		p = kvmalloc(size, flags);

	} else if ((flags & (__GFP_IO | __GFP_FS)) == __GFP_IO) {

		unsigned int nofs_flag = memalloc_nofs_save();

		p = kvmalloc(size, GFP_KERNEL);

		memalloc_nofs_restore(nofs_flag);

	} else {

		unsigned int noio_flag = memalloc_noio_save();

		p = kvmalloc(size, GFP_KERNEL);

		memalloc_noio_restore(noio_flag);

	}



	return __vmalloc(size, flags, PAGE_KERNEL);

	return p;

}





static int parse_fsid(const char *str, struct ceph_fsid *fsid)

{

	int i = 0;