Messages in this thread Patch in this message | | | Subject | [PATCH] drop_buffers() shouldn't de-ref page->mapping if its NULL | From | Badari Pulavarty <> | Date | 27 Apr 2005 16:53:38 -0700 |
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Hi,
I answered my own question. It looks like we could have pages with buffers without page->mapping. In such cases, we shouldn't de-ref page->mapping in drop_buffers(). Here is the trivial patch to fix it.
Thanks, Badari
On Wed, 2005-04-27 at 16:38, Badari Pulavarty wrote: > Hi Andrew, > > We ran into a panic in drop_buffers() while running some networking > tests and I am wondering if this a valid case. try_to_free_buffers() > seems to call drop_buffers() even if the mapping is NULL. drop_buffers() > seems to de-ref the mapping. This is causing NULL pointer deref. > > But, is "mapping == NULL" still valid case here ? Can we be in the > code to drop buffers and have mapping NULL ? We would be in this > code only if PagePrivate() is set. Can we have page private with > out a valid mapping ? > > Thanks, > Badari > > int try_to_free_buffers(struct page *page) > { > struct address_space * const mapping = page->mapping; > .... > > if (mapping == NULL) { /* can this still happen? */ > ret = drop_buffers(page, &buffers_to_free); > goto out; > } > } > > drop_buffers(struct page *page, struct buffer_head **buffers_to_free) > { > .... > if (buffer_write_io_error(bh)) > set_bit(AS_EIO, &page->mapping->flags); <<<<<< > ... > } > > 1:mon> e > cpu 0x1: Vector: 300 (Data Access) at [c00000007ff4b620] > pc: c0000000000bd524: .drop_buffers+0x40/0xcc > lr: c0000000000bd614: .try_to_free_buffers+0x64/0xf4 > sp: c00000007ff4b8a0 > msr: 8000000000009032 > dar: 60 > dsisr: 40000000 > current = 0xc00000000fe7e040 > paca = 0xc0000000003da800 > pid = 40, comm = kswapd1 > > 1:mon> t > [c00000007ff4b920] c0000000000bd614 .try_to_free_buffers+0x64/0xf4 > [c00000007ff4b9c0] c0000000000baadc .try_to_release_page+0x88/0x9c > [c00000007ff4ba40] c000000000099418 .shrink_list+0x3a0/0x608 > [c00000007ff4bb90] c000000000099a04 .shrink_cache+0x384/0x610 > [c00000007ff4bcd0] c00000000009a4d4 .shrink_zone+0x104/0x140 > [c00000007ff4bd70] c00000000009aaf0 .balance_pgdat+0x270/0x448 > [c00000007ff4be90] c00000000009ade4 .kswapd+0x11c/0x120 > [c00000007ff4bf90] c000000000018ad0 .kernel_thread+0x4c/0x6c > > > > - > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com> --- linux-2.6.12-rc2.org/fs/buffer.c 2005-04-27 07:19:44.000000000 -0700 +++ linux-2.6.12-rc2/fs/buffer.c 2005-04-27 07:20:34.000000000 -0700 @@ -2917,7 +2917,7 @@ drop_buffers(struct page *page, struct b bh = head; do { - if (buffer_write_io_error(bh)) + if (buffer_write_io_error(bh) && page->mapping) set_bit(AS_EIO, &page->mapping->flags); if (buffer_busy(bh)) goto failed; | |