On 2020/1/1 2:14, Eric Biggers wrote: > From: Eric Biggers <[email protected]> > > Without any form of coordination, any case where multiple allocations > from the same mempool are needed at a time to make forward progress can > deadlock under memory pressure. > > This is the case for struct bio_post_read_ctx, as one can be allocated > to decrypt a Merkle tree page during fsverity_verify_bio(), which itself > is running from a post-read callback for a data bio which has its own > struct bio_post_read_ctx. > > Fix this by freeing first bio_post_read_ctx before calling > fsverity_verify_bio(). This works because verity (if enabled) is always > the last post-read step. > > This deadlock can be reproduced by trying to read from an encrypted > verity file after reducing NUM_PREALLOC_POST_READ_CTXS to 1 and patching > mempool_alloc() to pretend that pool->alloc() always fails. > > Note that since NUM_PREALLOC_POST_READ_CTXS is actually 128, to actually > hit this bug in practice would require reading from lots of encrypted > verity files at the same time. But it's theoretically possible, as N > available objects doesn't guarantee forward progress when > N/2 threads > each need 2 objects at a time. > > Fixes: 95ae251fe828 ("f2fs: add fs-verity support") > Signed-off-by: Eric Biggers <[email protected]>
Reviewed-by: Chao Yu <[email protected]> Thanks, _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
